evenfall

Bos, After reviewing the FAQ page I would say it is very well written and an accurate mirror of discussion that goes on in here. This forum is all-inclusive for all variations of Gaming and NGS recovery of what we refer to as "Benchmarks". There is no requirement or pressure for anyone to do either. Some discussions are more technical than others for those who are attempting to recover and report to the NGS, as it can be more technical in nature but that too is reflective of details given in the FAQ. It is a fair use of the forum to talk NGS recovery, after all, the NGS does provide the game pieces and hunting data in the first place, and the players who choose to recover them are providing a community service which is consistent with the overall philosophy of Groundspeak. Groundspeak also hosts forums that are specifically dedicated to Ham Radio, GPS education, Ecology, the USGS National Map, etc. All seem to be spin-offs that fit the overall theme. I have seen some confusion as to what kind of recovery is being intended, and there is disparity in the "criteria" for each kind of recovery, but that too is covered in the FAQ. The simple truth is that the criteria for recovery _is_ different for the game than it is for NGS recovery. In most cases, the discussion in the forum is about doing it all as best anyone can for either kind of recovery, although it does often include the history involved and other information pertaining to the recoveries. It is difficult to speak to any given tread in a forum and remain inclusive of all players of the game when taken as a whole yet, many people find this discussion interesting. Most importantly, the forum works pretty well for all the ground it has to cover. Everyone seems to be having fun following their version of hunting and reporting benchmarks, in the way they choose to have fun whether their preferred variety of the game is one way or the other. The FAQ page is hosted by Groundspeak and was written and edited by both Groundspeak and people who play the game here in this forum. All are hobbyists, some are also surveyors, or work in related fields. As it is and as things are, it serves as a FAQ page pretty well as long as people are inclined to read it in the first place, but many here know it is often overlooked and we happily help all comers either way, no matter what their questions may be. Until the Benchmarking forum has additional topic forums added to it like the Geocaching Related Topics have, we really have no choice other than to discuss all our topics and musings in here. It is but one forum for a multi faceted, often confusing topic. Each person who starts a thread sets the tone of their desired discussion. It is rare in this forum to see any topic starter close a topic, even if the topic is taken to a place other than originally intended. It is a very broad Topical Forum when taken as all inclusive of the various ways it reveals itself. Until the if and when a decision is made to add additional topics to the Benchmark Hunting Forum is made, I fear more than one FAQ (for those who do read it) would be even more confusing than what we have. Many choose to post photos of their benchmark recoveries in lieu of a cache log. It is the same kind of proof a cache log would provide if there was one, but there is no rule or requirement to photograph anything, that is something many people just elect to do. Most Importantly, I want you to know that this should be first and foremost fun, and that you should not feel pressure to play in any way other than the way YOU like. Just because some may take the game more seriously than others is no reason for anyone else to participate in any other way than feels best for them, whether they have recovered 8 or 800 of these things. I hope that helps to answer your questions. Feel free to ask anytime. Rob

Hey All, Taking Callaway's example a little further, here is a link to the other side of T17S R20E This location is six miles east of Callaway's photo. While we look at that photo on topozone take note of the angle of the Mexican Border, which is also the border line known as T17S. These Maps are oriented North Up so the border line for California is on a bearing of roughly 260 degrees. Meridians are laid out as a line running North/South. Baselines East/West. So all the boxes of this coordinate system are for the most part laid out square to this orientation. With 270 degrees being true west, this border is on an angle. I know this seems obvious, but when you look at the Cadastral Marker again, notice the angle of the line drawn on the marker. It matches the angle of the border line. and this marker is a point on that angle, that is why they refer to it as an Angle Point. Once this line travels six miles further south it will likely become known as T18S and will increment higher each six miles south, and once it crosses the San Bernadino Meridian The Range markers will change from RxxE to RxxW. As angle points go in other cases, A surveyor will use the term angle point to describe a point, or place on a curve or tangent where an angle that changes the current direction, bearing or heading is located. One of the interesting features of cadastral markers when you find them is there will be lines on them that depict the lines that make up the township and range system where it is located. At a glance you can see on the monument which area is marked in the territory. If the station is properly oriented, they can help orient you as to the direction things are if you know how to read them. Just remember the usual north up orientation. Rob

Hey All, This is a Cadastral Survey marker, and it belongs to the Bureau of Land Management, General Land Office. It is a marker used with PLSS survey work, and used as the frame of reference for legal property descriptions. This is an angle point like Callaway mentioned, and many of these Cadastral Markers are set on top of a stand pipe like this one is. This Angle Point is number 7 within this particular Township and Range. This type of setting is generally not stable enough for geodetic work. The NGS has often set their markers at the POB of the meridians and baselines, but since these Cadastral Markers measure Township and Range location which is basically a series of six mile by six mile boxes, they don't really apply to kinds of control used for geodesy. This particular marker belongs to San Bernadino Meridian. It is located 120 miles east, and 102 miles south of the San Bernadino Meridian Baseline, which is considered the POB, or Point of Beginning for that particular meridian system, one of three in California. In a nutshell this marker helps to define the Township and Range system. It is a sort of coordinate grid system, but not to be confused with UTM. It is not a Datum, yet it has used Datum down through the years to help map and define itself. If you are interested in learning more about this system used for defining real property, here are a few good links. The online information regarding these is quite exhaustive. http://www.blm.gov/cadastral/meridians/meridians.htm is a link showing all the meridians in all the states that use this system. http://www.blm.gov/cadastral/ is everything you will ever want to know about Cadastral Survey work. The Manual of Surveying instructions 1973 found in this link is very detailed and is also available as a .pdf download for those who may want it. It is a large file, or if you like, there is also an html version also. http://phoenix.gov/ASSOC/plsshelp.html is a brief overview of the Township and Range System. Enjoy, Rob

Graveyard Mom, Here is the most important thing you might like to know. There are 2 different kinds of discussion happening in here. One is the game of hunting the benchmark and listing it in the geocaching website as a find for yourself. The other thing is that some of us choose to optionally report the survey marker finds to the agency that owns them. The National Geodetic Survey (NGS). The criteria for doing one as opposed to the other is a bit different and when taken all at once, and can be just plain confusing to the casual observer. To add it can be difficult to differentiate between who is talking about which aspect of the game, sometimes we kinda do it both at once. I want to just say to try and hang in here with us, at the root of all this stuff we discuss we are having fun. If you just want to play and log your finds at geocaching that is great! You are not under any obligation to log your finds with the NGS. If you don't feel comfortable doing that, that is fine and actually understandable. As a community online, we are a group that finds all this fun challenging, perplexing, historical, educational, competitive, and I am sure I am leaving lots out. Just wade in to the level YOU like. Most importantly, just have fun! If you have any more questions please ask away. As you can see, we just love questions in here! Rob

Hi Zhanna, Sure, I think I can clear this up. The disc in your photo, labeled ET5 WAC 1963 is a USGS standard Bench Mark disc. Unlike others from different eras which do have the words Bench Mark stamped right into them, this one is just like the one that Patty (Wintertime) posted in a different picture later in this thread. In both pictures, yours and hers, the Station Discs have the words ELEV. FT. ABOVE SEA machine stamped on the discs, and that is a standard stamping on many USGS Bench Mark Discs. From the USGS Topo you uploaded, we can see the location you refer to with a triangle and the BM EL=2218. That the actual station disc should have been marked ET6, is you and Rich's very cool find, yet the location you found does correspond to a location which is stated as a known elevation. The elevation seems to fit the Topo, and the Station was obviously mis-stamped. It is a Bench Mark, but in this case on the NGS Control Diagram you obtained, it is also shown as part of an Electronic Traverse as well. Without the Data you have, Most others would not be so safe to assume this as they would not know what ET stood for and even then assuming that is no guarrantee. USGS Stations Marked TT were often meant to mean Transit Traverse. In this case, You knew there is more data ascribed to the Station than just Bench Mark Data. I was saying it is not safe to assume that there is more data ascribed to a station than what the station type on the ground makes obvious. The electronic traverse performed by the USGS was likely performed for checking the physical distances between the stations to compare how the benched elevations fit the topo mapping data. It is a form of "Open Traverse". They are just making sure their elevations hit the contours and the distance between these stations on the ground will scale favorably to those on the maps. The interesting thing about an open traverse is that there is no real way to properly check it for errors unless you perform it over again. We would usually have to perform the open traverse more than once to check for mistakes. To add, there are plenty of ground and heat effects that can harm accuracy when EDM is used over long distances on an Open Traverse. The further you go, the larger the margin for error. It is not like the kind of Horizontal Control we think of when we think of NGS Control. Comparatively the NGS Triangulation is a known point on earth exact to within inches or less, the USGS Open traverse is really just a basic measured distance between two points that help them check to see that the maps fit the territory. In my post, I was saying as a for instance that we are familiar with NGS Triangulation Station Marks. We see them in the field all the time. We get so used to it, that we automatically assume things we think we can expect at a glance. Yet an old CGS Triangulation station can have Bench Mark Data ascribed to them. Hypothetically speaking, it may have started life as a third order Horizontal Station, then lets say in 2001 a crew sets up a GPS over it and sends in the newly collected data. After the NGS checks the Data, it now becomes a B order Horizontal Station with Vertical Order of say Second Class 0 quality. Yup, It just became a NAVD 88 Bench Mark. Since GPS isn't leveling or traditional triangulation, but can derive data in 3 dimensions at once, an old dog of a certain type can learn a new trick. So what I meant is that there can be more data than we assume is there, but that is never safe to assume anything until we see the data ascribed to the station. I know of a few CGS Reference Marks that have been leveled to Vertical Order First Class 2. Who would have thought a Reference Mark Disc is also a Bench Mark? But so are many top bolts on Fire Hydrants. It goes to show you never can tell. I guess I was collectively referring to several things that had been raised in the thread by others as well. I used your for-instance as an example and to stay on topic as I attempted to explain answers to the various questions raised by others. Mike Raised the point that it is a generic disc to be used for all control. I was raising the point that it is never safe to assume we know what the control is until we see the datasheet. Rob

Ok, went looking for a couple of Mike's great photos... Here is a good look at some landmarks that NGS used as intersected points. Just a page out of a Guide and that also has a Link to Zhanna's site where there is more like it. Here is a good example of how to go about photo documenting a destroyed Station Mark. Thanks in advance to elcamino for the reuse of his posts. He has another example of a destryed station somewhere but I was unable to locate it. I hope these examples help those who may have been curious. Rob

Hey All, I am going to try to answer this for you in terms of NGS recovery only, so please if you just want to game, please realize I will be speaking in terms that are stricter than the game. The Game rules are not as strict. NGS Station Discs cannot be declared destroyed unless you can furnish unequivocal proof to the NGS. This means physical evidence, such as the station itself, or a series of photos that document the station as removed from it's physical setting. While back, elcamino had a great post of how he documented this with photos and I will see if I can find the link. If your photos show the area and the disc in a legible way as being physically removed the NGS may consider removing it from the database. if you send them the actual destroyed station or contact your states NGS Geodetic Advisor, (see the NGS site for links to that) then they will remove it from the database. If this kind of proof, a burden of proof if you will, can not be provided to the NGS then they prefer to forever think of that station as not found. This policy is a good one as it prevents people from easily destroying a spatial reference system through vandalism, erroneous not finds, or without bothering to look for it. On the subject of landmark stations like the Water tower, but also many other types of tall objects, the NGS is aware these "intersected points" are not owned survey markers, and things change. Some landmarks has monumented station discs but that is rare, and even then the station disc itself was not the intersected point. The datasheet will tell the tale in the recovery narratives. The NGS will consider destroying a Landmark if you document the situation well and submit it to Deb Brown. You can photograph the area documenting where the former landmark was, and try to photo the GPS showing the coordinates, preferably in NAD 83 Datum and your display set to ddd.mm.sss mode. This will match the NGS methods of using their data and save them from either not destroying the landmark based on your submitted work or having to take the time to convert it all to check your claim. The more we can do for them in order to make our case, the better. In the case of a water tank that was a NGS landmark which has been destroyed but the foundation is still there and there are NGS station markers in the foundation, you can follow the path I outlined. Submit the proof that the tank is gone on the PID that describes the tank itself but that the footings are still there and the survey markers are too. The Survey markers in the footing will have a different PID (point ID) than the tank. I would submit a recovery with photos of the brass disc station markers to the NGS. This updates the database and adds pictured of the brass disc station. Again, regarding the tank itself, email the photos to deb brown, after you read the deb brown pinned link to see how, then document the missing water tank with PID and all. In the email, make your case along with the photo evidence. The NGS will look it over and decide. Geocachers have done a lot of this sort of work and it helps purge a lot of no longer useful data from the database. Good luck and if you have any more questions please feel free to ask. There are lots of people here in the forum who love to help. P.S. for the game of Geocaching Benchmarks, you can list the tank as destroyed and the brass discs on the footing as a find. :-) Rob

Wister, What you found does belong to USACE, The US Army Corps of Engineers. They are involved in hydrodynamic studies of most all of the nations rivers. It is a flood control thing, They study the river when it is in it's bank and try to figure out what happens when it leaves the bank. Mostly Bench Marks to help ascertain river levels flood plains and gauge stations. The DOD reference on the Datasheet was a later addition, but the Army is under the Department of Defense. This is a pipe cap type of monument. These have not been used much in years but there are still some around. They usually just don't seem to last well. The metals in these pipe cap stations usually didn't stand the test of time and they fell out of use. USACE has plenty of Bench Marks out in the field they use for their own control. Not all have been submitted for use in the NGS database. Rob

This is a fun post Zhanna! As Geocachers we refer to all survey marker as benchmarks which is fine, we all know what we mean but in the strictest of terms the terminology is more specific. When is a Benchmark not a Bench Mark? Chicken, egg, geodetic surveyor? In the strictest terminology, and as far as NGS survey markers and other agency control that meets NGS criteria are concerned, surveyors refer to these monumented locations as Stations. There are different kinds of course but for most of us who are dealing with Geodetic Monuments we will primarily find Triangulation Stations which are Horizontal Control, latitude and longitude, and Bench Mark Stations. A Bench Mark to a surveyor means one thing, Vertical control. It is not a generic terminology, rather it is a point of known elevation. Other types of stations are used to measure Gravity and Magnetic fields. These Stations are also often triangulated and double as Horizontal Control. Azimuth Marks, which were set to aid in getting a Station "dialed in" as to it's orientation so measurements could be taken with less effort, and the Math would be the same each time this was done. These are most usually only found on first order horizontal stations but there are other instances too. Then of course there are the Reference Marks which point to the station, and all of these station monument types can vary as to the era the marker was set. Zhanna has a wonderful website about many things survey, and she has a page that shows drawings of the various Marker types the NGS has set down through the years. If you would like to look at it, it is located Here. These Stations are monumented with a plan in mind. The Surveyors, specifically the Party Chief knows what they intend to do in advance. A survey party would usually be interested in performing specific types of survey. Vertical teams don't do Horizontal work and vice versa. it is specialized. A Bench Mark monument will be set in the ground, drilled in a sidewalk or even vertically in a wall by a crew that places monuments in a place that has been pre determined. Then a leveling crew would come through the area to ascertain and document what the actual elevation is at the surface of the station disc's highest point. A monument crew would also be sent to establish a Triangulation Station, In the ground or drilled into a stable surface if other, but never set vertically. This would be a big excavation in the time when an underground mark was also set as well as a surface one, not to mention the RM's and Azimuth... In either and any case, the station has to be in place prior to the time the measurements to it are made, and the monument will be of the type that reflects the type of data which is to be ascribed to it.. You can't measure something that is not there. Then a Survey crew will come, center their instruments over the station mark with perhaps a plumb bob in older times or an optical plummet on newer instruments and begin the planned triangulations. If the plan is to monument a third order station, the standards for meeting the requirement is followed. A third order station has had at least 4 separate triangulations performed to establish it's position. Second order stations had 8 separate triangulations, First order stations had 12-16 separate triangulations performed. Then the heavy duty math begins... All the triangulations are then taken together as a least squares adjustment and so on... A and B order Stations are horizontal control from GPS observations. They may be established as such or upgraded from previous numerical order triangulation, and as an added feature from GPS technology, they can have Bench Marked Elevation Data ascribed to them as well. It is important to treat the data separately. They are first most a form of horizontal control that happens to have elevation data ascribed to them. As to other Agencies and their monuments, the same criteria and high standards NGS requires of their own settings are required to be met in order to be submitted to the NGS database. In the Case of a lot of the USGS stations that are submitted to the NGS for inclusion in the database, most are Bench Marked Elevation Control points, the USGS did not do as much triangulation, and to be sure much of it was not done to nor meant to be done to NGS standards. Many different agencies did perform Survey to NGS standards and when it was submitted to NGS and found to be up to standard, it was included in the database. The pictured USGS disc is Vertical Control disc, a Bench Mark for known elevation. It says that it is of course but we should not assume it has any other kind of data ascribed to it either. Why the designer put a triangle around the cross hatch sure seems to send a mixed metaphor when industry standard symbology is considered, but it has been their design for years. Each agency has it's own unique ways and we all get used to it. As Mike said the (+) is the point to which the data is ascribed and all measurements are to be taken. The Disc has the words Bench Mark on it and that is strictly Elevation. The Elevation is no longer stamped on monuments because we have learned that Datums change and the world is not a static place. I would need to see the data sheet as a surveyor in order to see how or if this station will meet my needs. Now Zhanna, did you see that BM running through the high brush? Was it making noise? Did you have to lead that BM much in order to bag it, or did you startle it then drop it standing still? I can hear the call! (<Quietly with Aussie accent> There we were mate... trying to sneak up on the wiley bench mark. I'm tellin you mate, this is not your ordinary kind of mark, oh no! this one is trying to hide it self on the topo!! We've compared it, and we know it is on the loose, but not for long!! Crickey! We bagged it! Benchmark hunters rule!!) What a High adventure! Hehehe This was a killer post Zhanna, Thanks! I'll save the Bugs Bunny, Elmer J. Fudd version for another go... Rob

Paul, What I understand, from people I have spoken with at NGS, is that they have discovered a quirk in the online recovery program. They say you should keep typing until you get to the end of the line. Each line can hold 426 characters and there are 15 total lines. They ask that you not put hard returns sooner, because you limit your available space. If you need more than 15 lines to re-describe a Station, and it can conceivably happen sometimes, just contact them directly. They may just ask that you email the recovery and they will submit it for you. I wouldn't use a program like Word to rough these out because Word will insert a hard carriage return where ever you set the page to wrap the text. I use a basic text editor and I have it show me word and character count, as well as all the invisible characters so I can see where I put my returns and spaces, then I paste it to the recovery form and tweek it from there. Patty, It was a really good question. I am glad you asked it because it helps clarify what helps a description. I recently recovered a Station that had not really been recovered since 1953. The Power Squadron said they found it 2 years ago but I have my reservations about that. It was a really tough find. Most of the old description was unusable, in fact the reference mark is not findable, as there is nothing left that references the RM. It was poorly described to begin with. The Power Squadron would have had to perform a lot of measuring with tools they would be unlikely to have in order to find it, I had to uncover it from under 8 inches of top soil and cut a 2 inch diameter root that had grown over the top of the Station. There were so many roots in there that there was no way the station had been recovered in less than 2 years. Then all they submitted was that it was found. They entered no narrative entry. Yeah Sure. I used a good bit of 15 lines writing a good description for that Station. Mike also makes a great point. Another Station I recently recovered was a 2nd Order Triangulation Station with 2 Reference Marks, Both of the RM's were set in drill holes in the curb by the street. The Station itself was under 4 inches of sod between 45-50 diagonal feet away from the RM's. simple enough right? There were 2 pages of narrative recovery listed after the station's basic metadata... It was described in so many ways... They measured from a ton of objects all around, some of which were gone, others not. Many difficult ways. Can you imagine a line projected south, 29 feet from the curb which is 17 feet west of a line projected south from the approximate centerline of a sidewalk leading to the entrance of a building across the street? Ok, I'll bite, the building across the street has three entrances. Great. Which? Oh and the Station was 29 feet... South... From the back of a 6 foot wide sidewalk, not the curb. The curb is a funny object too because we Surveyors have many ways to reference from a curb so naturally that starts us to thinking, Face of Curb? Top Back of Curb etc... Hmmmmm... But the curb is definitely not the back edge of sidewalk. In this case there was no described method to do it the easiest way. Nobody ever measured the bearings and distances from the Reference Marks to the Station. Duh. Reference Marks in broad daylight, shiny, happy 60 year old reference marks in the curb... I spent 50 minutes triangulating the station position to find it in the first place using all the esoteric methods that the former describers used. then once I found it I spent less than 5 minutes taking bearings and distances to the station from the reference marks. I included that in my recovery along with other repairs. Now it is a simple two tape find. The RM's are for finding the Station so Mike makes the best point, describe toward the station not away from it. On how many recoveries could we often repair this little mistake on alone? Edit, Spelling. Rob

Patty, You have raised a great question! I am going to answer in a way that may also help others who may be wondering how to approach their own recoveries like this as well. In this case, since you are no longer in Yosemite, you could say something like this; The original wooden witness post was not found. two new witness posts without signs have been placed near the Station. One is a concrete post and the other is a metal post painted red. The metal post is the closer post to the station and the station is situated between them. If you do know the directions and distances or even the post heights, you could simply say something like; The description is adequate with the following updates. The original wooden witness post is not found. A new (or two new) witness post(s) have been placed near the station. A concrete post, 6x6 square which stands 2 feet high is located 7.5 feet southwest of the Station and a metal post currently painted red about 2.5 feet high is 3 feet southeast of the Station. It is cool to know the bearings and distances, even cardinal directions are helpful, but if you don't have a way to check them there are other ways that can help. Any way that a description that can be improved and updated can be helpful, as the world changes and some of the described items can be removed or changed in an area over time. if I am stumbling through the woods and I know I am looking for a couple witness posts and I see them from a ways away, that is an aha moment, especially if I am looking for a Scaled Bench Mark that could be anywhere near by. Triangulation should have coordinates which are more accurate than consumer grade GPS can do so it may be easier, but in the woods without a good GPS signal, perhaps knowing I am looking for a couple posts, one red and one concrete can be super helpful. On the NGS recovery page you can put in up to 15 lines of text. The key to it is just be succinct and descriptive. Please feel free to write as much as is needed, that you feel will help improve the description. If the description is adequate, you do not need to say that, nor do you have to write anything at all, just click the button that said it is found in good or poor condition, and then on the next page mark the button that appropriately defines the Station's GPS usability. In the cases where you do find a replaced witness post, feel free to take a bearing from the post to the Station Mark and a distance between them and add them to the description if it has not been done. All it takes is a compass and a tape measure and it is a helpful addition to the Datasheet. In your photo it shows that the Station could cover with needles and such and so it can speed up the hunt to know where to look if it is covered. There is no standard practice for where to put a witness post. There are schools of thought. Some feel it best to put it close to the station to aid in finding the station, others feel that it should not be too close, but in the vicinity, so as to avoid vandalism to the Station... In either case, and we will see both schools of thought in the field. Either way if we improve the Datasheet the person looking for it will have the most up to date aid to help them find it. One other thing that is helpful is to look on the NGS Datasheet to see if the Latitude and Longitude are scaled. This will define the station as a Bench Mark Station in most cases. (some GPS Station Observations include both Triangulation and Elevation data) If they are, we can improve upon this by adding our GPSr's waypoint coordinates for the station to the description, in NAD 83 ddd.mm.sss format. That suddenly becomes a digital witness post that will be in the datasheet forever. It isn't necessary for a triangulation station however because the coordinates are already accurate to at least a half inch accuracy already. Overall, most Surveyors will appreciate the details, because as you know, sometimes it takes everything there is to help find the station. In 25 years, who knows which details will still be true? Rob

Anthony, My Bad! Thanks for correcting me on the name. I knew what I was thinking but I didn't double check my thoughts... You are right about the coastal work in Alaska in the 1930's but I was thinking about both Triangulation and Leveling. The initial coastal work in Alaska likely only consisted of Triangulation. Differential Leveling is something that cannot be derived from any other observation other than a known, Bench Marked elevation. This means we have to start somewhere which is known and perform leveling on to where we need it to go. As a rule, in order to tie into a Datum or a reference of some kind, and we usually do have to, we cannot pick an arbitrary place and assign an elevation to it and go off leveling from that point, but rather we have to go to the nearest Bench Marked leveling we can find and continue the work of bringing the leveling into the area we need it and establish the monuments that we need to refer to regularly in that locale. Since NGVD 29, a vertical datum was established in the Continental US and lower Canada, It seems that Bench Marked elevations would have to be brought from there. I was just curious as to how. You have found dated Bench Mark data for 1943 and that would be the timeframe just after the highway was built, or rather blazed through. As for the Triangulation, It could have been brought from Alaska, and that would seem to be the easy way, but I think it would have followed the highway route. The coast mountains would have been a lot of work to triangulate over even for 85 miles. Fairbanks was where they were going with the road, but they may have triangulated in from the coast near Whitehorse and went both directions from there to complete the work. Then there is the other matter of how the highway was built to deal with. The Army built the highway from both ends and met in the middle. That means they had to coordinate both ends by fly over at least, in order to meet in the middle at the same time, or at least it would seem so. They would have to establish some triangulation in the area to map this accurately, and it would have been all NAD 27 Datum Survey at the time, and any which lies in Canada is now abandoned by the NGS. If the Canadian government did not adopt this survey work, and include it in their data, then all that old control is still NAD 27 control. I know they put the whole road in like a logging company would. They just took the easiest, most direct way they could find to do so. They didn't need established survey to determine ruling grades and curves, you make the curves fit what you need and keep to good established engineering practices for minimum radiuses and then perform simple on site leveling and do a little rise over run math to keep the road grades from becoming too steep for the trucks. This road was really a dirt road to begin with. It was navigable, sort of, and they surveyed what they did afterwards, obviously to facilitate mapping and further designed improvements. Improvements such as engineered steel or concrete bridges, super elevation for curves, widening, drainage, and maybe to blueprint what they did. A detailed survey of the entire road itself would likely be performed at some time later and that would not have been a C&GS activity. The US Army may have done so, after the CG&S established survey control, as it was a military road then, but it is a wilderness road in two countries now. The C&GS was likely in the area at the same time the Army was, so it just makes me wonder what all they did. If they collaborated, and how. When you think about it, 10,607 U.S. soldiers built a road 1,522 miles long in 8 months. It seems to me they would have had to have triangulation established in order to survey the road from end to end at some point, but in 8 months and ahead of construction? Doubtful. It is a US Government road project, and they would want to Map it, there are all the grades and bridges and drainage which require engineering. Engineering needs Survey to plan with and so it goes... Shazam! Infrastructure! I cannot find anything in the NGS History about how they took part in this project and the History of the Alcan does not speak to the role the C&GS played. Sure is fun to wonder about it though. Rob

A History Question for DaveD, Dave, if you have the time or may know off hand, the Alaska or Alcan Highway has had me wondering a few things that this topic brings to mind. It is true that the USCG&S did the initial geodetic survey work along the Alaska Highway route probably to aid the Army Corps of Engineers in their road surveys. But when I think about the location of Yellowknife, Yukon Territory, That is a long long way from anywhere. (no offense Yellowknife) Leveling Standards at that time were from the NGVD 29 Datum, so I precariously presume all the elevations for that leveling would correspond to that Datum at that time, and still would since NGS does not continue to update the data. Perhaps the Canadian government has adopted some of this work for themselves. My primary curiosity is, what methods were used to extend established level lines into Canada, and this far into Canada? Did we come off of established control here in the States, or Alaska? I am not sure how much good control we had in Alaska at that time. Also, Where did we bring Triangulation in from for this project? Did the CG&S bring triangulation up from the south from perhaps Western Washington? Did the Canadian Government have survey that could be used closer to the area where the highway was being built? What quality triangulation and leveling would have been considered adequate enough and efficient enough to keep the project surveyed at the pace the army needed to go? I somehow sense that First order work would have taken too much time and cost too much. With 2300 miles between Seattle and Fairbanks, most of it in some of the toughest terrain there is to work in, it is apparent that this may have been no small undertaking. Have you any thoughts or info off hand? Thanks in advance Dave, Rob

Geo, PLSS uses North. A compass is not considered adequate for survey work anymore but at one time before we had the science available we do now, compasses were used to help determine a north azimuth in some instances. If you want to calibrate your compass this site is very useful: http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp If you just want to touch up your general knowledge on geomagnetism, then try this: http://www.ngdc.noaa.gov/seg/geomag/geomag.shtml Rob

mloser, No problem there! You were correct all along. I just wanted to help all the people who read your post, as well as those who will occasionally see the word Macadam in a datasheet know what it means. It is an accurate usage of the word, Just not a common usage anymore, and that is why an asphalt company could use it to make the name of their business seem unique. It could be an old business in your area at that and by carrying the old usage in their business name, the locals know what it means. But for the most part the Term MacAdam or Macadam has fallen out of use. It is all based on the name of a guy who pioneered the process is all. In the UK they refer to it as Bitumen. Here in the Northwest, Macadam is a word much like Geodesy... Say what? Asphalt as it is formulated today is an extremely high viscosity oil which acts like a solid at everyday earth temperatures. It is basically the product that is left over after the refining process has stripped all the other useful products out of crude oil. It is nasty stuff really. They add other additives and viscosity enhancers to it of course and many States and Municipalities have other specifications they like added to the oil so it performs better when used as a pavement surface. The Macadam side of all this is when they mix the oil at high temperatures with crushed rock. It is a science getting the hot oil and crushed rock to mix consistently at the correct ratios and temperatures. There are a few processes used to do this, MacAdam was responsible for the particular method he pioneered. I am sure some derivative of his method is still being used in some way even today. I have worked closely with road building companies down through my career, and I suppose I picked up a lot of trade magazines and looked through them along the way. Construction and Surveying is awash in an ocean of trade magazines. I would have to say that it would not seem like it as we drive down the road, but the asphalt industry is pretty technical. They do a lot of testing and formulating. They are always trying to engineer a better, longer lasting product. Rob

Casey and Geo, First Casey, you made the point that 1920 era datum were erroneous based on how they handle tidal uniformity. You are correct! But given what we knew at the time, it was a good system, and served a helpful purpose. Tides are not uniform as to height and timing at any two places along our coasts. It is a science in and unto itself as to how the times and height of the actual sea water levels are calculated. There are a lot of sources out there attempting to explain this concept. Factor in weather and there is more room for error. Geodetically speaking today, the term Mean Sea Level is a theoretical surface based on a single monument, it is not a component of the actual tidal waters, nor based on an 18-19 year average of all high and low tides at any one or 26 given locations. Nor is the reference standard for this Mean Sea Level based on how much water is in the ocean. (It could be based on this if you are a researcher studying how much water IS in the ocean!) These things are simply not a stable reference for geodetic purposes but some sources will attempt to define it this way. However NGVD 29, the old 1920's Datum was Sea Level based but averaged and computed based on twenty-one tidal stations in the US and five in Canada. 26 different, simultaneously adjusted stations. Tide was however affected by gravity too, and this system could not easily compensate for this because of the instability in the model. Taken together with older models, which define the Geoid, the Ellipsoid, actually thought to be a spheroid then, and other frames of reference, were based on the observations of the time. We really did the best we could with what we had and comparatively; we did pretty well at that! Mean Sea Level was not the same across the US as a belief, but rather made that way for the sake of mathematical reference. Today we use a different standard for Mean Sea Level yet we refer to it in the old way. You can google this definition and you will find many explanations as to what Mean Sea Level is. To be fair, I would say that many who have attempted to explain what mean sea level is, but most definitions seem to explain it in a way we no longer frame the reference. I have to smile upon them for trying. I sometimes wish we would call it something else today but it is what it is, confusion and all. For Geodetic purposes today these Datum are earth centered, and you can carry this over to GPS, mapping, surveying, and all forms of navigation, as they are all based on geodetic references, Mean Sea Level is now based on a fixed reference that does not move, One Tidal Bench Mark, Father’s Point/Rimouski, Quebec, Canada. All Leveling is based from there. But that was just leveling the Topographical heights of North America and is not the whole story. At any given point today, a frame of reference as taken by latitude and longitude will be necessary to calculate the GPS height for that location, as either above or below Mean Sea Level. GPS elevation is a component of several equations compared to the actual ground level (read Real leveled Topo, and referred to as the Orthometric surface) which was exhaustively leveled in the 1980's, the Ellipsoid Height, the Geoid Height, and a least squares adjustment taken to remove errors from the measurements. Mean Sea level is used to reference the elevation but it is not used as a part of the equation. Remember the earth's surface is the topographically leveled (meaning elevation determined though the method called differential leveling) earth we stand on, used as a frame of reference. It is the empirically leveled, monumented Bench Mark Elevation, and if not recently leveled it can be Adjusted. It is also simultaneously, the Orthometric Reference. The Geoid is that lumpy orb I referred to in an earlier post, which is a sort of ellipsoid that approximates the size of the earth, which isn't really a truly ellipsoidal shape because it is deformed by the forces of gravity. The ellipsoid is based from a smooth surface meant to be a model of the approximate overall size and shape of the earth as if the earth had neither gravity nor topographical features when compared to the actual Topographical surface. Geoid Height is a comparison of the geoid with the ellipsoid. Ellipsoid height is a comparison of the Ellipsoid with the topographical surface of the earth, or Orthometric surface. The Orthometric Height is a comparison of the Geoid to the actual Topo. Leveling is the most accurate way of determining elevation and was the basis for determining NAVD 88. It is not performed as a usual method of finding an elevation very often any more. The GPS uses the ellipsoidal reference, along with Latitude and Longitude. The GPS Satellite Constellation basically triangulates the GPS to a place and a height above or below the ellipsoid. This ellipsoidal height is not comparable to Orthometric Height, which is the actual height of the ground. This height has to be compared to a high resolution model of the Geoid, the gravitational model, which has a variable conversion factor based on any given latitude and longitude to convert an ellipsoidal height to an orthometric height. We have the capability to do this to a degree of accuracy that approaches that of leveling. Then we can do a leveling loop much like we can do multiple triangulation's and perform a least squares adjustment on the loop to enhance the accuracy of all our observations. Why do we do it this way? To correct the errors we see between the way we see the earth when we perform differential leveling on the actual surface (Orthometric surface), how a GPS actually sees the earth as based on radio telemetry (Ellipsoidal surface), and how gravimeters see the earth as based on measurements taken that base what we think form the shape of the geoid (Geoid surface). They all three differ a bit, but bringing the ellipsoid and the geoid together with the right models and formulas bring us to a single elevation. Again, for the sake of a uniform mathematical reference. Obviously what we believed back in the day and what we believe now are 2 different things. Geo, I hope the old model of NGVD Sea Level reference helps answer you. Your instance is really pre NGVD 29. I imagine they used a reference benchmark, which was of known height as compared to what was considered reference for that time. In 1899 the world was a smaller place and I imagine, even pre NGVD 29 and NAD 27 that the Tidal levels of the Gulf may have been a local frame of reference for the area at the time, again I imagine it was based on an averaged sea level of more than one place. This was probably averaged beyond the Gulf as well. The difficult thing about your instance is that here is a chiseled elevation that really has no Datum to reference itself against. It is not correct now, and was only correct for the duration the reference it was based on was considered correct. This is why a bench mark is generally not ascribed an elevation in person, at least not any more. We have learned we can improve upon all this, and as we do the number will change. A chiseled or stamped number becomes eternally incorrect with the first update. In closing, trying to explain all this is not really cake, and I may have made errors. I have proofed it but I may have overlooked something. If anyone has anything to add or feels that I may have been in error, please feel free to weigh in! Rob

Mike, I went to that link and was blazing along until I came to the The Jacobian Matrix, where I was met by a man named Morpheus, who offered me the choice of either a Red, or Blue Pill. Then my pencil broke. Now if we climb into the time machine and go back to say, the year 1900. The Geodetic Surveyors have a 90 foot wooden tower built over the top of a station which is to become a First Order Triangulation Station. They are not near a town, not really, and there is a heavy theodolite at the top of the tower they built from lumber they logged and cut near the site. They have 12-16 separate triangulation observations they have to observe to qualify this Station for first order quality. They are living in tents and use horses and wagons. They cook and eat camp style, and in fact they are likely living off provisions they brought. They have to feed the horses as well. Maybe it is a crew of 10 - 15 guys and some have to ride to the other locations out there somewhere to other towers built over other stations to help make observations. It is a wet October going into November, and it is not pleasant. Yet there are a few people on the crew who with a pencil and paper are doing, and doing all day long, some derivative of these least squares equations to bring the various triangulation's they have done to the one Latitude and Longitude they determine this Station to be at. And then they do it again. Today, we set up a GPS for a few hours, let the data collector have it all, pack up, drive back to the office and hook the data collector to the computer where we can parse the data any number of different ways before we drive home to our warm homes. Sure there is hard stuff but comparatively? It kinda makes me feel glad I have it this easy. Can someone loan me a pencil? :-) Oh, and um, a lot of paper too? NOT! Rob.

This is a great thread! Excellent info! It should Also be noted that the NGS only adjusts, or converts to NAD 83 and later derivatives which are updates to NAD 83, such as NAD 83 (1991) and the like as an example. NAD 83 is the North American Datum of 1983 and it is owned by the National Geodetic Survey. They created it and they work to improve it's accuracy. We should make sure we are setting our GPS to NAD 83 Datum when we hunt for Benchmarks in Geocaching, because it is the correct Datum to use. While it is true that we will likely be exceeding the accuracy of a consumer grade GPS device, it doesn't make sense to further degrade it either. There is a difference between WGS 84 and NAD 83 which is equal to approximately +/- 1 meter at earth center, which is something, depending on where you are on the earth, which can add or subtract 1 meter of error to the accuracy of your GPS both vertically and horizontally, all at once, if you are using the wrong Datum for what you are trying to do. The amount of error you get will vary from locale to locale. The amount and direction the error which is present when the wrong datum is selected will be hard to determine with a consumer device, but it will be present none the less. The WGS 84 Datum, Which superseded the WGS 72 DATUM is known as the World Geodetic System Datum. It is owned by the US Department of Defense and maintained by the Defense Mapping Agency. For those who would like to familiarize themselves with definitions for many of the items listed on NGS Datasheets, a good place to learn is here. There is more to the quality of a Survey Monument than just Adjusted. Rob

Ha Ha, That is good Mike! Yup, and in this day and age I would hope that the person who is being quizzed has a dadgum good answer for the trooper too! I laugh but it is like asking to be profiled badly. If they were not able to walk their talk, there would have been little keeping them from a ride in the cruiser. The suburban may have been the trump card! Some guys can look pretty shoddy in an old set of Filson tin pants and coat too... You never wash them, in fact they say you shouldn't... Boy they can get to looking bad. Heheheh Just yesterday I was looking for a second order triangulation with 3 RM's and an azimuth in a neighborhood watch neighborhood. I put my vest on and knocked on a few doors prior to proceeding. One lady grilled me pretty hard too. She did ask me if I had some sort of ID... I said I had a drivers license and I had a clipboard with some datasheets but beyond that, she was going to have to take my word. I don't blame her, it is her turf, not mine. But I did get to do my thing unimpeded. People go from looking at you funny to ignoring you. She wound up walking her dog and asking me more questions about the survey marks. One RM was monumented in her back porch step and she had been stepping over it for years. She had no idea. Now she does. Rob

For the people who may wonder, or be interested what an adjusted coordinate location is, or means, here is an attempt to explain. It is a rather big picture to draw and there are probably a few good ways to draw it but here goes... The NGS has programs which have the ability of taking a coordinate location from a given datum and converting it to a coordinate location of a different given datum. It could be considered as simple as converting NAD 27 to NAD 83, or NGVD 29 to NAVD 88, and it sort of is, but it is also more involved than that. This means I can start with a first order horizontal control station (triangulation) which was originally surveyed into the NAD 27 datum, meaning I should be reasonably safe to say that I am less than 3 centimeters of the actual latitude and longitude of a place on earth. I can then adjust it to the NAD 83 Datum which means physically the monument is still in the same place but the datum causes the station coordinate to change to match the the way that location is accurately located in the different datum. There will most usually be a shift of some sort. The important thing to note is that you are still accurate to the 3 centimeters even after the shift because we are adjusting a first order station. The same level of accuracy is maintained when the "adjusted" type of conversion is used. Briefly, a datum is a mathematical baseline reference which expresses something. in this case the something is called a geoid. A geoid is the hypothetical surface of the earth that coincides everywhere with mean sea level. (if you could imagine two earths, with one being as it is, mountains and sea, but with no water in the sea. Then an earth that was the same size, and identical as to the overall shape of the orb, but it was entirely "mean sea level" size, with no mountains or under sea valleys. Simply combine the two, slide the two together all at once with both sets of feature displayed. That would be the frame of reference used to express Latitude Longitude and elevations both above and below sea level. all at once.) Now to add to that, we have more than just one model of "the geoid" It is interesting to note that the gravitational pull of the earth is not uniform in all places and so this means the earth is not a perfect sphere. it is really more of a sort of lumpy orb. We keep re evaluating it and determining that we can define it better. We attempt to describe the shape of our lumpy orb. Then we use a datum which we use to describe that geoid. That means we use a coordinate system to define where points and places on the lumpy orb really are. We are also finding ways of mathematically improving the ways accurizing the datum, by constantly measuring and getting more and more accurate instruments to measure it. When we compare the orb changes in terms of defining the Geoid and then take our way of measuring that with the latest Horizontal and vertical Datums we are actually closer to where we really are than we have ever been. When you see the word "ADJUSTED" on the datasheet, in tech speak, yet as simply as I can state it, it means a program took the old coordinates in NAD 27, converted it to NAD 83, then a least-squares adjustment is performed, which means all of the unknown parameters in the mathematical equation (read Calculus) are simultaneously adjusted to minimize the sum of the squares of the residuals in all of the measured quantities (weighted inversely proportionally to their variances if the measurements are not equally accurate), with suitable constraints among the parameters to force any theoretically required relationships to be exactly true. And since I am a Surveyor and not a Geodesist, that is the best I can do on it. It is not math for the meek, and not math I do. It was converted in a highly accurized way. I can say however, using tools that the NGS has on their website, that where I am sitting, I am Vertically 3.547 feet higher in elevation than I was when I compare the NGVD 29 Vertical Datum with NAVD 88. I can use a program called VERTCON to "adjust" my elevation to the latest datum and here I am. Depending on the Value of the Bench Mark, NGS could have used a least squares adjustment in the calculation of elevation, as part of a conversion as well This set of figures only applies to my location because of the "Lumpy Orb" factor I spoke of in the Geoid Model. For the horizontal conversion from NAD 27 to NAD 83 I can use the NADCON program for my Latitude and Longitude and find NAD 27 - NAD 83 shift values of N Lat: 0.64777 W Lon -4.46385(secs.) All based on improved geoid models and accurate datum. All this specific shift only applies to my location alone and could begin to vary a bit as little as less than a mile away from my location. The monuments in the field are where they are, but in re defining the geoid and datums, the coordinates change, but not too drastically. The hope is that they collectively become more accurate all the time, even without the virtue of being re-surveyed in years. I mean we are talking feet, and yards worth of accuracy between datums, but not miles. And improvements are performed on the accuracy of the NAD 83 datum all the time. Even at that, the earth is not static and man too is introducing both errors as well as more accurate ways of seeing all of this, all the time. Rob

Bill, Yeah, I know. I was thinking it would be something that would help some people. It would be compulsory, something a person could print off themselves, for free, only if they wanted. Something that would help them explain if needed. Carry only if they wanted. A way to help some people say, "thats my story and I'm sticking to it" as if they needed to... I only benchmark hunt and as a surveyor, well that is pretty plausible for me. I mean it is in my Job Description. I also know I can still be run over by a car while wearing safety orange. But if I was a geocacher and I was perhaps wearing military surplus camos because they are good cargo pants, and I happened to look a bit off in some neighborhood as I was rummaging through an Ammo Can that is sort of hidden, oh, say near a public school. I know my own neighbors and they are aware of who lives here and who doesn't. I know they watch and so I assume all neighbors watch pretty much anywhere anymore. Who knows who will look intimidating enough to cause someone to give the cops a phone call. I wonder what a law enforcement officer would think? I mean of course they would not profile me and wonder a thing right? They were just stopping by to see what a strangely dressed person wearing paramilitary clothing was doing in an ammo can in the brush near a school. Heheheh I bet I would get asked some tough questions, but hey. It is starting to look a lot like an old Bugs Bunny Cartoon from the get go... Heheheh. It was just a thought. Not a rule or anything. I don't want more rules, I just want everyone to be safe and have fun. It was just a way to perhaps help. Maybe some officers would not care, maybe some would listen. It was just that two different cities in our country used rather excessive force on a geocache within 2 days time, and then the terrorists made another announcement. We live in interesting times. It's all good. I am going to have fun anyway. Rob

Ted and all, Thanks for that thread. It raises some good points, but perhaps it is time to revisit the discussion a bit more. It would appear that it was discussed last time a bit, and then things sort of trailed off to nothing and that was the end of it. This time we may see that happen again too but either way it is worth the provocative side of causing to consider our own safety yet another time. It begs the questions, how can we make this better and safer? How can we be better ambassadors of our hobby in the community? How can we lift it all up? It is not a debate really, just a kicking around of ideas and that is a good thing. A Geocaching ID would not be a legal ID or take the place of one, but under the stress of a tense moment it would have Geocaching Logo and the web address, your personal user name. The only way you could print one for yourself is by logging into your personal user account. You will have had to verify your email address and all. It is not ID per se, but will show that you have taken steps to officially affiliate yourself with the game so that you can participate in the scoring and the info which only logged in members can have access too. If need be someone could look into the fact as to whether you actually are a geocacher or not. Once they log in, if they were unfamiliar they could then become familiar with what geocachers do. It would verify your story. They could see your score or recoveries, the photos you may have uploaded etc. Another aspect of having the ID card sharing the opportunity to have fun with others. After all, what a cool way to say yeah I am looking for treasure, or a survey marker! Here is the website to go to to learn how to play! Just show them your card. It can serve a few purposes. It would never be a get out of jail free card, just a way of corroborating your reason for being where you are and what you are doing there. It would be no different than a card issued by the Red Cross which states you have been trained in First Aid or CPR, or that you are a Life Guard, No different than a AAA towing card, or affiliation with any other club or group. It is just a piece of paper that has information about what is going on and where more facts can be found. It is obvious we live in interesting times. We have no right to do anything just a granted privilege. We are completely enjoying Geocaching because we are good stewards and friendly people, and that is a good way to be. I just would like to see if there is a way we can better look out for ourselves when we are confused by others who may not be familiar with out brand of fun. For now, I have printed a few pages of the Geocaching Website and I am taking them along, Just in case they are needed to help me prove that I am just having fun. Is it a good idea to familiarize local law enforcement officials and departments with what a Cache looks like? What the Geocaching Cache stickers and decals look like? What we do? Why we like it? How we can help them look and keep watch on the areas we frequent? Can we prevent the Homeland Security oriented agencies from misinterpreting our intentions by partnering with them in ways that show them we add value to what they do and to not mistake a cache as a weaponized Ammo Can or Tupperware? (is that person hiding ammo in the woods?) In fact in these times based on the superstitions of homeland security, is hiding an ammo can as a cache container even a good idea? I mean it is an item that comes from the military side of things. Could it be misconstrued or send a wrong message? We get what we negotiate. As I said yesterday, and I still think it best, feel free to let people know why you are where you are and what you are doing. This is a time, or instance when asking permission in advance is easier than asking forgiveness. You may convert them to geocacher in the process, and it may keep you out of trouble! :-) It really does come down to us, one on one, and it sure beats the alternative! It is post 9/11 and we are living around people who feel a lot of fear. I too could be mistaken by someone who views all people through the eyes of fear, and I want every resource I can get to justify my actions when my actions are somehow misinterpreted. I sense I could be misinterpreted even easier after the headline news of today. That is just my choice, I don't want to curtail my enjoyment just because people don't understand my form of fun. I am pretty sure that people who are up to no good will want nothing to do with offering an explanation to anyone, they will just want to get away. We have nothing to hide other than that which we are trying to find! :-) As an alternative, can do nothing too. Not that we can prevent every bad thing, but either way, this can happen again. Edited to say, please have fun, be careful and stay safe! Rob

I hope I am not speaking out of turn, as I do not hunt geocaches myself. I just do the Bench Marks. It seems to me though that there are a few thoughts I would like to share in the parallels that can be drawn to Bench Mark Hunting and the Survey field as well. First, It is sad that this happened. I read most of that thread and as unfortunate as it was it still happened. However, no matter what comes down, the onus is on us to dot all the eyes and cross all the T's. If we want geocaching to keep it's good name there are things we have to take responsibility for, collectively and personally. Most who work in the Survey Field will tell you, trespassing is always a dangerous factor in our work. Sometimes we don't think we are when someone else will. You can be met by unhappy property owners and well, it is more a matter of when, not if. The difference is that we look like surveyors when we are met, not just like people who are wearing street clothes and are perhaps tresspassing... There are plenty of places we need to stand and walk through to do the work and it isn't unlike Geocaching. We really have to ask a lot of people permission to enter their land to do our work. Our hat is in our hand, we are humble and kind, and we are mindful to leave things as we find them as much as is possible. This instance has me thinking, Should we place a cache without permission, Should a cache be approved without showing that permission was obtained, and since the activity seems to appear suspicious to the uninformed and Law Enforcement officials in this Post 9/11 age, would we as Geocachers be safer to ask a property owner permission to recover a cache before we do, just so they know we are there and why? That way they know that suspicious looking person hunting a piece of Tupperware or an Ammo Can is cool? I am sure that the approvers are doing their best to verify things and that most Cache placers are obtaining all the necessary permissions when they can or if needed but we have to look out for ourselves as well. We are all ambassadors of the hobby. I hope all the people who place a cache use an approved Decal from Geocaching, I mean It looks Uniform and Official. It has the web address and the logo. It has the place to put the Cache approval number, and if Law enforcement officials are familiar with the logo and stickers since they are uniform in style, then they can easily identify what they have. I realize this may add cost to those who hide caches, and make their own labels to save money. They may even disagree with my opinion as well and I am prepared for that, but I am thinking about public support for our hobby in how they perceive us, and our good standing in the community as well as with Law Enforcement Officials. As with the Bench Mark, The NGS often had to obtain permission to set the markers, and often we as Surveyors have to ask permission to enter property to use survey markers. I know for strictly just Recovering Markers for Geocaching I have asked several property owners permission to do so. I have also contacted City and County Municipalities as well as the US Coast Guard and the US Army. I felt it best to cover my butt! I have been asked by many a passerby what I am doing, and I have an Official NGS data sheet Close at hand to show them, and then I explain. Everything I do may be cheaper than a ride in a Police Car or a Fine for Putting the Police through an expensive maneuver to deal with me for what is a really harmless hobby. The National News and the Government is reminding the country every day to stay on the look out for suspicious activities and I suppose we really do have to come to the conclusions that this can apply to us. We all have to take all the care we can to play not only by Geocaching's rules but we have to also look at how we play in societies rules as well. I think we do this pretty well for the most part and do it well as a rule, but it may be time to ask ourselves when we play, "what can I do to make this safer for me?" I mean ultimately, I could be the one asked by the police what I am doing. Do I have a good answer? Just a closing thought. I know it may add to the things we carry with us, but perhaps if we print out a copy of our Geocaching User ID, and perhaps the front page of the game website, or the page with the rules for geocaching along with the web address so we can have a form of proof with us that we are affiliated with this sport. I hate to ask Jeremy to do more than he does but perhaps he can code a page that is a link to the signed in member user ID page that will take info from our membership data and place it on a small wallet sized, or credit card sized form we can print out in full color so we can laminate it and carry it in our wallets. It has our user info, the web address for geocaching.com and the official logo. All printable, then maybe we sign it and we take it to the Officemax and have it laminated. This way when we are asked we have something in our wallet that says we are just people having fun. Certainly all the info on the card would be easy to corroborate through the official web site. Yu are the only one who can log in as you, after all... Just my thoughts. I could be way off, but I feel this is worth thinking over. Rob

mrh, Nice Find! TBM is an abbreviation for Temporary Bench Mark. They look like what you found and can be found with variations on that theme, or can often be a railroad spike driven in a tree trunk with a piece of lath nailed above it. The elevation at the top of the spike is written on the lath so that constructors can use it as a point for their own leveling, and calibrating their own instruments to known elevations during construction work. The one you found is a lot more official looking than any I usually set. For the most part the tree will not be a stable place to place elevation control for long so it will only be accurate for long enough to do a job without needing to be re-checked. There are however other ways to set TBM's. Hubs and Hubs with a Tack, Hubs with a Blue Feather called Blue Tops which though not a Bench Marked Elevation per se, it is a form of certified grade, which is certifying that a road sub grade has been surveyed to a finished design sub grade elevation. The feather is nailed to the top of the wooden hubs so that you do not lose the location of the hub as you spread material over it to attain the design grade with a bulldozer or road grader. A hub may also have a lath set next to it explaining what it is, as well as any other info pertaining to it which help constructors arrive at a designed elevation or contour. A Nail driven in a street or side walk can also serve as a TBM and even a painted circle with a dot in the center can sometimes signify a TBM. That is a very temporary BM. Mainly they are set as a temporary known point of elevation part of a Survey or some other task at hand. One of the funny things we say in the industry is that if you are waiting for a dump truck to bring you something or take material away, just drive a hub in the ground and a truck will be by in five minutes or so to run that hub over. :-) Boundsgoer, I am sorry, but I don't have a picture. You are correct though, BLM GLO was the primary agency to set Bearing Trees as part of PLSS work dating well back to at least the early 1800's. I will have to keep my eyes open for the Markers I saw. It has been a while. Rob

Black Dog, I have to laugh but yes. Whacky as it seems, A "Geodetic Azimuth" was considered to be in the direction of due South until the NGS changed the practice officially to North in the 1970's. If you talk to people at the NGS about it, especially those who have worked in the field they will laugh and probably tell you a story or two about a kind of personal hell they have endured because of that very quirk! :-) You have to pay rapt attention or the math will go off somewhere... What I mean to say is that back in the day, an azimuth mark or even an azimuth spoken of was to be considered to be south of the Station in question. This is why, for the most part, you will find most all the first order triangulation stations, and I say first order because they were usually the stations that would have them, with Azimuth Marks set, will have them set to the south of the station if set prior to the 1970's, most of the time. Just a quirky practice that once was but no longer is. Either way it still has it's legacy. It is sort of cool, and you will see for yourself if you pull the datasheet for MZ1557 that the RM's are found in "geodetic azimuth" and there is the answer to the mirror image. All Geodetic Azimuth means is in the direction geodetic surveyors commonly assign the azimuth for the record. In reality you can assign any direction as an azimuth, but common practices kept everyone thinking in a uniformly standardized way. It is a good thing to keep in mind when searching for RM's that seem to be hard to find. A geodetic azimuth when based on the date of monumentation can mean that the bearings will be in reverse of standard thinking and modern practices. What ever happened to Survey Tech anyway? He hasn't posted in about 18 months... Oh by the way Dave, Peaked Mt 2 RM4 Was found last in the 1977 recovery. You are the first since then. Rob