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Everything posted by evenfall

  1. FtMgAl, I understand the where of you speak. I too have have done what you did while in college. I still do it as part of my work. In fact thanks to automation, Today we often do it alone, One guy is the whole crew quite often. Today After working in the Laptop, making sure all the points i had to survey were properly assigned, I set up a robot for my GPS so my Rover could see where the Sattelites wont, up close to forrested area. Hubbed and staked 1000 feet of road, offset for curbs on both sides of a road, Centerline grades and super elevation transtition points, Points of curve, points of tangent etc. I had to Pound all my own hubs in hard soil and write all my own sticks, tie on all the flagging, lug all my gear, Write down all my work, develop a point sheet and cut sheet for the contractor... yada yada... The drugery of the old school rear chainman has not gone away, In fact, as you can see, the rear chain and the party chief are now often the same guy. In fact, they expect as much production as ever. I still have to keep my Machete sharp if you get my meaning. Either way, I know what I do makes a difference, and I think there are other careers that I would not enjoy, so I do this. When I think of myself in the middle of a large office building in a cubical under florescent lighting as opposed to being outside doing battle with a blackberry bush to place a corner stake... Well, the blackberry bush ain't so great, but I think I'll keep it in trade for the cubical. that is just me. Go ahead and laugh, I am! Constuction in the real world happens and progress sometimes take a Bench Mark out. I know of a few here on GC.com that have been reported good until something came along in the last year and changed that. This is just another database Bro, not unlike the NGS database. Things that once were found can become lost, just as easy as that. Say la vie.... When it comes down to it, those old timers you apprenticed under years ago did rub off on you. You know how painful it can be to make double sure, and internally it is the way you feel it should be. Good on you! Sure there are short cuts and ways of bending the rules, but you and I both know shortcuts are throat cuts. This is a game to some and an engineering challenge to others. I will continue to recover Bench Marks the way I feel I should and I will report them as such. If someone reads my recovery and feel it was the most helpful and accurate, then I did my job. If someone learns from the methods I use that is cool too... I learn from others as well. This is not about looking over my shoulder. I set my standards. I feel when it comes right down to it, your personal history, honesty and integrity will be your guide.
  2. I am going to have to second the motion of looking at geocaching.com. I have been for a long time, well before I joined here. I look at it like this. I check NGS online for the latest in the database. I also look here because it gives me a little street map and a maybe if someone has recovered it. I can about drive to it with the little map. Further, if it has been recovered by a geochacher, and they uploaded a pic of the mark, I may just about be able to walk up to the mark. What a time saver! Is there a down side? Well, the Geocaching Database is an older one than the NGS but has a bit different slant. Like I said, the pic is nice. Especially if there is a pic of the mark and a pic of the area the mark is in. NGS has no pics, however that may be changing... On the downside, "I found it" is not too descriptive but ahhh What the heck, they found it _recently_ and so should I. As for the NGS database. Well, it is the Reference Standard, but I have to admit, if the USPSQD reported the mark missing, I have a habit of looking anyway as I have found many of their missing marks in my career. They don't always get it wrong but they dont always get it right. Scroll up this thread, catch the PID for the Willamatte Stone and check the NGS Database. Would you agree with the 2004 recovery? But look at what we as geocachers have been able to determine. I think the Geocacher tries harder. The payoff is reporting the mark found. Geocachers seem to try pretty hard to find a mark. This brings me to a point I am making here. This Hobby has the attention of both Some Surveyors and those who work in that field, as well as NGS. And as time goes by the word will continue to spread. The integrity of many of these recoveries is really in the geocacher's hands. As an added challenge to the recovery of the old data, I would like to encourage people to go look anyway, even if it has been reported lost long ago. There are changes in the environment that cover and lose marks as well as uncover and find marks. You just never know. If you find a lost one, You put a Mark back in the Database that we all can use. That is a cool thing! Rob
  3. Continuing on this train of thought; Ok so there you have the criteria. It is clear to us that many Bench Marks truely are destroyed, but unless we can provide physical proof of the Actual Marker to the NGS as such, they will only allow them to be not found. This safe guards against the practice of Not Founds being logged as Destroyeds and truly screwing up the database. I have found Not Founds. So have many others. It is easy enough to note in the Text Record that a structure was deystroyed or the brass disc has been removed from the setting it was in. This will explain to the next person looking what the latest info is. If the NGS feels in their determination that a reset and recalibration or a new PID with monument needs to be replaced in that location, they will send a crew to replace it. In the case of the Willamaette Stone, well here's the deal. NGS, and C&GS as it was known back in the day will "commandeer" different things they find to hopefully be stable and lasting in the environment to use as locations that they could affix Reference Data to. Sadly however, Nothing is forever. This Monument never belonged to the NGS so it cannot be returned to them as proof of destruction. in fact, a portion of the broken original monument's base was used as a drill hole for the current monument. You could try to make a case for the destruction of it, but it is an NGS judgement call. This Monument, over 50 years ago was reported to only have a view to the southwest. That limits its use greatly. and it is not suitable for GPS. it really is of little value for NGS purposes, keeping in mind what the NGS mission is. In my experience when Bench Marks have been this altered, then NGS either performs a reset with a new PID, or a new name and a new PID. In either case, this Bench Mark is now just a record of the past, and no good for Geodetic service.
  4. CallawayMT, I think it is very cool that you went to the trouble to write the BLM. To be certain, this monument's location serves as the Initial Point for millions and millions of legal property descriptions all over the Pacific North West. It is a very, very important location. This is a great example of the kind of footwork that sometimes needs done to sort out and get at the truth. You also learned what was needed to be known. This "Specially Manufactured Monument Disc" is NOT the original Benchmark, as well as the history of the current station. That said, here is the deal. For Geocaching purposes, we must take a little pause. There is more than one force at work here. Many of us love hunting Bench Marks and we take it seriously. We know that the original was Vandalized in the 1980's and this NON NGS Benchmark Disc was put in it's place. So we think those who recover it are recovering nothing, and we are technically correct. But there are people who could care less or they are looking for a Cache near this loaction. Some may find it with the family and it is fun for the kids, do not know the lowdown and are not all that interested in this sort of thing but what the heck, log it anyway. Maybe it is important to show the kids how to log the cool find too. We will never change their minds, and one look at the Ceocaching Log on this PID will bear this out. There is a long list of people who both do and don't know the difference. What is the harm, geocache-wise in letting them think what they want? It is meant to be fun in the first place. For us true Bench Mark enthusiasts, We hunt the hard ones anyway, not the ones with their own custom walkway leading right to them. Since we are not perfect ourselves and trying to do our best, we can't really drum too loud, we all had to start sometime. I work in both Surveying and Heavy Construction, and I still learn something every day. Nobody starts out a Pro so there is no need to be too hard on ourselves. Officially, and for those of us who take it serious, AND FUN, I too would log this Destroyed on Geocaching because in truth, and by definition. it is, and that is the description that is the best fit on geocaching.com For NGS Purposes. this Monument is no longer in the state it was when the C&GS originally made their Monumenting Log entry in 1903. It is now a completely different style of monument. It is therefore Not Found. Unlike the one you mentioned in Boise Idaho where the monument's brass disc was gone, but the drill hole or concrete post was found. A new brass disc can easily cemented back in and the station rechecked, but the station is still there. I would report that Poor, Needs Maintainence and state why in the description. On the Willamette Stone, In it's original form, the Bench Mark was " MARKED BY BRASS SCREW SET IN CENTER OF TOP OF CUT STONE POST" which at one time projected 1-1/2 feet above the ground. This also means that the elevation for this PID is wrong, no matter how much care was taken to replace the brass disc in the right place. I am sure it was professionally surveyed in, and is fine for the other purpose it serves but it is Lost for Geodetic purposes. The current Monument does not match the description at all and I could not use NGS data for accurate survey from this location. The NGS Monument as described is NOT RECOVERED, NOT FOUND. If the NGS were to re-evaluate this station, due to the many changes it would likely be a reset, and likely would be assigned a brand new PID. It could be renamed MONUMENT RESET or MONUMENT 2. Most likely it will be reported not found and left in the database as such as the location is not all that survey friendly. We could call it Poor, disturbed, mutilated, requires maintenance, because that is partly true. It could be resurveyed and it's position corrected as it now exists, But the original monument is gone as far as the description is concerned. so in the most true sense, as described it is not recovered not found. Though it is not likely going to be used for modern geodetic work, there is no point in leavng the database as is. The information in the Database is not correct at this time. In closing, Remember to check the NGS website and run each PID as you go. the latest info is there. This PID will give us all a laugh and maybe we learn a lesson here too. Ok, we all know it is important to read ALL of the the details in their entirety so we know what the Bench Mark really is. If it does not match the description anymore, then it is not the Bench Mark. So how does this happen? "STATION RECOVERY (2004) RECOVERY NOTE BY US POWER SQUADRON 2004 (RHC) RECOVERED IN GOOD CONDITION." Yes this is the latest recovery for the Willamette Stone, and yes it is incorrect. Nope. It is lost, even though there is a monument there. Did USPSQD do the research that they should have to keep the NGS Database accurate, _before_ they logged this incorrectly? The Integrity of the NGS database, and Quality Assurance that goes into that is largely up to those who submit data. This is why the public cannot simply submit data for destroyed marks. If I were recovering this station as a geocacher, the recovery would read as follows: "STATION RECOVERY (2004) RECOVERY NOTE BY GEOCAC 2004 (YOU) NOT RECOVERED, NOT FOUND. The ORIGINAL 1903 STATION WAS VANDALIZED AND SEVERLY DAMAGED. IT WAS REPLACED IN 1988 BY A CUSTOM MADE COMMEMORATIVE BENCH MARK DISC MOUNTED FLUSH WITH THE GROUND IN THE BASE SECTION OF THE ORIGINAL STONE MONUMENT. THIS STATION IS NOT SUITABLE FOR GPS OBSERVATIONS. ORIGINAL STATION IS NOT RECOVERED AND REPLACEMENT STATION WILL REQUIRE MAINTAINENCE FOR ACCURACY AND GEODETIC PURPOSES. This has been a fun thread! Thanks! Rob
  5. ArtMan, You made a great point with the Yes and No, and Geocachers reports do have value. As much as anybodies. But let me bring a Surveyors Perspective. I am aware that Geocachers find Benchmarks and I do look here as an aid to finding them if I need. You Bet! On the point of taking photos, Your picture can also show that the mark is "Really Not Found" but here is what is in it's stead, lost, or why it was not recovered. Local Knowledge is also super helpful. I went to the NGS site and ran the PID for the chiseled square you shared with us. This is a very cool for instance and I will get to why. Picking what you descibed to us apart, (as this is what surveyors do to descriptions) You tell of the bridge being replaced in 1973. Ok I can assume either you are a Local and know this or you have been to the bridge and saw the 1973 formed into the concrete on the Bridge. The latest recovery for this mark does not state this. As a Surveyor, Sitting in my office preparing to survey near that bridge and looking for control I can use, I will be impressed to know, no matter who reports this that in their report they file that this bridge has been reconstructed in 1973. This staion has been lost and cannot be found. and reported as not recovered. Of further use to a Surveyor would be that there is some other Bench Mark installed in a different location of the bridge. I would report where on the bridge it is located and what it does say and that it does not seem to be in the NGS database with an assigned PID so it will not be confused as NGS Control of any kind. A Local Surveyor may know where to obtain Information on that mark instead. They would also not want to use it by mistake without accurate control. It happens. We could agree that it is destroyed, However the NGS will not allow anyone to file a destroyed Bench Mark report without meeting strict criteria, and you need the actual Bench Mark in order to do that. And so does the NGS. Since we never will have it and neither will anyone else, this station is lost, and not recovered with a reason why it was not recovered. In recovering all this info, Before I submitted it officially via the website recovery form, I would email Deb Brown at the NGS with submitted photos of the A the location where the mark was described to be and is not as well as all other good photo information proving your point. B, the Date of reconstruction on the bridge with Photo of this as well. C, The descriptions and location of other Marks on the bridge that have no PID and that you attempted to verify this. D, who those Marks may belong to if you can tell and E, State the obvious, that the station is Lost, Probably Destroyed and you would like her advice as to how she would prefer to have this station officially documented. Part of her job is to help make these judgement calls. She may even make the determination that the mark truly is "Destroyed". Just remember, there is no need to email NGS if the Bench Mark is a no brainer Not recovered. Just record the best, most accurate info you can. It is easy to do it by just trying to describe the Recovery or Non Recovery in a similar way that others in the NGS have. Try to emulate their manner. Be as brief yet descriptive as possible. As a for instance, If you were to go to recover a Bench Mark that you found the two reference marks for... as it had them, and they both pointed directly to an UGLY bramble of Blackberry bushes. I mean truckloads of thorny debris and hours of clearing to find this Bench Mark, as you have determined from the Description and your measurements that it is way back in there, You can report this to the NGS. Report that you found RM 1 and RM 2 Good as described and that the BM is located approximately 17 feet from the edge, inside a Blackberry Bramble from RM 1, 23 feet from the edge, inside a Blackberry Bramble, The station is likely undisturbed and was not recovered. If you report this you verify that the RM's are good and point to a tough mark to recover, that you didn't recover. I mean it is sometimes reported in the database that a Benchmark once placed on unused land is now under someone's Yard in private property and permission is not granted by the home owner to hunt for and recover it. So why not report a blackberry bramble? If that is what is true in 2004, then it is. It is the latest attempt for recovery, the current state of the area and a really good reason for not finding it. (I can tell you many stories of hacking Blackberries to find nothing, and or place something. It is rarely ever a joy. NOT Pleasant! The best time is in the summer when they are ripe. (for obvious reasons) I can tell you, I will never Volunteer to recover anything inside a blackberry bush. If you pay me and send me in there, then that is another story.) Having the information you know will impress surveyors so much that they will not waste any time looking for this mark or possibly being fooled by the marks that are chiseled into the new bridge. The marks on the new bridge are not HV2358 and some people could miss that and mistakenly use what is there. I would be impressed to not waste the time. It will shave more than minutes off a job more often than not, if they are using NGS control for help. As for the street address idea, That is very helpful. It can get someone near a Bench Mark with Map Blast. Street addresses seem to remain much more stable to locate in a future tense than particular Trees, Telephone poles, wood based structures, and other forms of landscaping. It fact the landscape is hiding tons of these things. And what will the landscape look like in 30 more years? You can change every single thing about a house and yard but it will likely keep the same address. The CenterLine of Road, Center of Man Hole Covers, Corners of Storm Drain Grates, Top Bolts of Fire Hydrants, Back of Curb, Back of sidewalk, and other permanant utilities are likely much more stable to use as well. Feel free to describe where you measured from, the Compass Heading, as well as the distance to the Bench Mark and Feel free to measure to the Bench Mark from at least two different things you find that you think will be permanant points you feel others can easily locate. Also, set your GPS directly ON the Benchmark itself as well as any Reference Mark and Azimuth Mark Discs and record the NAD 83 Coordinates AND the level of Accuracy you had at the time of recovery. By rights, Anyone should be able to about walk up on it with a consumer grade GPS at that point. When it comes to Volunteers doing this recovery work, don't sell yourself short. Licensed Surveyors and those who work in that field are not paid to recover these Marks. They do so as a courtesy to NGS to help maintain the integrity of the NGS control. So they and others can continue to use it. Only the NGS is paid to recover when they recover. And they recover as a matter of the course of performing their Mission. The USPSQD is a fully volunteer organization, no better than a Geochacher, In fact their main claim to fame is teaching boating safety. They Report NGS Bench Marks as an "aid to navigation". The Geocacher has a reporting Agency Mark with the NGS too. It is GEOCAC. In fact, I love recovering stations USPSQD and others report as not found. Here is a throwdown, when you see that a mark is not recovered, go try anyway. I have even found some that the NGS didn't find and reported lost, but that is not easy as they will make a very good attempt to locate their marks. Bottom line, The history is cool and it is challenging fun! Thanks for raising a great point!
  6. Tireman, Here's the lowdown. The only Database that geocaching.com is using for Bench Marks is from the NOAA/NGS, and it is not the most current copy. In addition, If geocaching.com has ever updated the NGS database, I do not know. It is certain that there are a large number of survey controls out there in the environment that will not be found in the gc database and likely never will. For instance, there is the U.S. Public Land Survey System, which is otherwise known as the Township and Range System. it uses Meridians and Base lines. Most large cities have established their own contol for engineering and Platting. Most counties have their own control as do the public utilities. Most State Departments of Transportation have all their own control. Each branch of the Military has it's own control for it's own civil work as well as for going to war anywhere in the world. I could go on, but when you parse it down to small stuff, a Private Surveyor/ Enginering firm establishes unique control for housing platts and for the building of Skyscrapers. So there is a lot of stuff out there in the environment we could find. In the case of going to Topozone and finding BM in a contour map. It is likely you can go recover these BM's but the were also likely set By the Provider of the Maps to Topozone and that agency is the USGS. This is what the USGS has to say about its Bench Mark Database: http://interactive2.usgs.gov/faq/list_faq_...swer.asp?id=323 If you like, Recover them and save them in a folder or a Database of your own until such a time USGS makes their data available. You will be far ahead of many. Of Note However. the USGS has down through the years had a habit of stamping elevations on some of their Bench Marks. I cannot stress this strongly enough. This Data is in error, do not use it, ever. Many of these Marks were Minted Prior to 1986 and set to NAD 27, a Datum that is no longer used. The elevations were also pinned to NGVD 29 for elevation purposes as well and that too has been superceded. That stamping cannot be adjusted in the field. NOAA/NGS Bench Marks do not suffer this as they never had a value "physically assigned", and though many have been placed prior to the use of the current Datum's in use, the Database can be updated and adjusted. All the best and latest information is on the Datasheets. The reason I point this out is that just yesterday, I recovered a station whose Datasheet indicated a Four foot change in elevation simply from being adjusted by an updated Datum. And what's worse is that the amount of error changes from location to location. There is no one formula that corrects this. It depends on where you are located. The NOAA/NGS Data is the most accurate database for terrestrial control there is, It is the one you are out searching for on geocaching.com In any case, maybe we will be able to hunt for Marks in other Databases some day. For now, I would collect them anyway, you never know.
  7. This is a cool question, and believe it or not, there are solutions. As discussed, we can bring the Bench Mark to the contractors attention. Interestingly enough Benchmarks are Valuable to Constructors As everything they build is usually to an engineered plan. If they know that Bench Marks are present in thier jobsite, they will often take pains to preserve them. There may be carelessness in some cases and contractors who wont care, and sometimes a bulldozer or excavator will remove a monument because the monument was not located in the first place. In the initial process of clearing land, many unknows become suddenly, Known! The operator simply does not see it and unknowingly removes it. at that point it is too late. When it comes to Contractors, the Residential Builders are the least likely to need the Bench Mark and the least likely to care. Commercial Contractors live and die by controlled survey. They will be interested in saving that mark. In either case, some will care and some will not. In the case of Roads, say for instance in Asphalt and Concrete work, a riser will often be installed or lifted so that the work can take place without covering the monument, and afterwards the monument can still be accessed. In this case, depending on the grade work that will need to be done for these driveways, the fact that a Bench Mark will be in the way need not be a problem. If it is in a location that is in the way, yet below the grade of the new drive way, a piece of pvc pipe can be placed as a riser and a monument cover fitted to the top so grading can continue, and access to the monument be retained. If it is in a location that is at or above the grade, the asphalt or concrete work can be incorporated up to the edge of the Bench Mark as long as care is taken to make sure the road around the monument can help keep it stable. In some cases the grade of a driveway can be altered to accomodate the Monument so that a monument cover can be incorporated over it. A case scenario where we may not have a choice in saving a Bench Mark would be if say a mark were located in an area where work was to be performed that involved lowering the grade elevation by a large amount. Nobody is going to leave a Bench Mark sitting on top of a 16 foot pillar of dirt just because it is a Bench Mark. Usually the benchmarks are A, removed and not reported, B, reported to the NGS as an Oops, (the forgiveness rather than permission approach) or C, the NGS is contacted ahead of time and the NGS sends a State Advisor out to have a look. (this is how the ones that say RESET happen.) If you think a Bench Mark is in jepordy, and you would like to see it preserved, diplomacy is always best. If you want to become involved yourself, call it to the contractor or land owners attention, with a gentle reminder that it would be cool if it can be preserved if possible and leave it at that. Then go to the NGS website to find the State Geodedic Advisor for your state: http://www.ngs.noaa.gov/ADVISORS/AllStates.shtml#ADVISORS Then contact them and advise them what is happening. Be sure to tell them what the PID is, the location, the description, what you feel is about to happen to the monument, or even how to find you so you can show them personally, and then they can officially take over from there.
  8. Post removed as it was a duplicate posting to flood errors on the Groundspeak website Sorry for the inconvienience.
  9. Post removed as it was a duplicate posting to flood errors on the Groundspeak website Sorry for the inconvienience.
  10. Well there are several answers to this, and it depends on what you are trying to do. First off, for many years, these little discs and the measurements made with them were how we knew the faults, such as the San Andreus and any others moved and how much. Getting back to which are geologicallly more stable than the others is a mater of simply retrangulating them to get a new fix on position and elevation, and then updating the data. Bench Marks in high movement areas are as a matter of course, updated much more frequently. Some discs which are in high movent areas got a lot of updating through re-leveling and triangulation, and some still do, as any benchmark can be used to do it, but some are used more than others due to location, ease of use etc. Much of the work that monitors geodedic stability is monitored through CORS stations for the NGS and other agencies too as we have learned. Then there is the work of monitoring the movement of shorelines as well. In the case of a local surveyor using a 50 to 75 year old Bench Mark that has not been checked in a while, well things are not so bad as you think. The Criteria for seting a Bench Mark is pretty stringent, the book on how to do it is available from the NGS as a pdf file here: http://www.ngs.noaa.gov/PUBS_LIB/GeodeticBMs.pdf So we know that the attempt to be as stable and accurate as possible was made when it was monumented, and unless it looks disturbed, and from the recovery notes, we have to trust that it will be good enough for our purposes. It is rather like an order of relativity for the Local Surveyor. He is not using the station to Trangulate for geodetic reasons. Rather he is likely to use it as an elevation reference to traverse from, and he may use it and another to perform a triangulation for local civil work, but getting back to the relativity part, it is a local area survey, and so if the benchmark has moved by 2 hundreds of a foot in 75 years, it is good to know, but that wont hurt you when you are solving for the rise over run for a sewer line, A storm drain, Grading a road or setting the site elevation for a building pad. Besides, the likelyhood that the benchmark is what it is supposed to be is very high. So the answer is, Some stations are checked more often than others, and the stations that are not are still in many ways pretty accurate when where they are located and the local conditions taken under consideration. In the end, it can depend on what is being attempted on the survey, and who the survey is for.
  11. To answer Geotrailblazer, the reason why the NOAA/NGS would want us to send in Pics and Coordinates for found marks is simple. These Marks are still valuable for many reasons, and many agencies continue to use them, even though they are not currently used for monitoring the Geoid. Certainly the NOAA likes having the help without having to budget for it. The price is right for them. They probably are not accustomed to many volunteers in thier agency. Yet it is good volunteer work, that is not like the usual volunteer work. It is good that it is being done. Armed with a recent handheld GPS position Fix In NAD 83 Datum, you can get anyone with a GPS similarly set within 15-30 feet of the found Benchmark. Simply Load the coordinates, Set a GO TO and it is a no brainer. A Picture proves the Mark is real, and found. Not claimed found but rather, Really Found! The adages of Seeing is Believing and A picture's worth a thousand words, both apply. The want a Pic of the mark and a Pic of the surrounding area. Armed with that, Almost anyone could find it. Could save a lot of people at work a lot of time searching for something that could be easily found with updated info.
  12. Geodetic research has always sought ways to do things better, often by using the latest technology. Many Bench Marks were set as disc locations and used as stations to Triangulate the shape of the Geoid, against other disc locations and tall structures of the day. The Latitude Longitude Grid, The Coastlines. and other geographical features of the land were measured using these Bench Marks. Early on this was done with tall wooden towers erected over the Bench Marks and later on, beginning in the late 1920's lighter, more portable Bilby Towers so as to get above the terrain and to see as far as would be needed to do those triangulations. (these towers are why there once were 10 lb plumb bobs. It took a heavy bob to be stable over a Bench Mark During an instrument set up when it was suspended from 60-120 feet of rope.) Heavy but accurate Theolodites were packed up the towers to make these measurements. Much of this work was done at night with Kerosene lamps and later battery operated lights so as to avoid distortion from Heat haze. Later in the late 1960's and the 70's it became Lazer technology. (this is where the term "height of the light" originated yet we still use the term in the field as another way of declaring the H.I or Height of Instrument) (The H.I. is needed to be known to make the computations, and removed from the equation to give the reading for ground level. Recording the HI allowed others to replicate, or check the math) The Math, early on was calculated by hand. Yup, Logarithmic, Triginometric, and Geometric Calculations. Pencil and paper, all day every day. Several computations were completed per day on a good day! later there were Crude Computers in the 50's and 60's later Calculators (Hewlett Packard anyone?) to help with the math and finally PC's and larger computers. Then GPS came along with a complete network in the late 80's and the technology to utilize it got better and better. Today most work on the Geoid is done with these stations: http://www.ngs.noaa.gov/CORS/ The cors station. Continuously Operating Reference Stations. Real time GPS at it's finest. Back in 2000 President Clinton signed a bill that removed "selective availability" from the GPS system, and that is why our GPS is as accurate as it is today. With the thousands of Bench Marks in existance, or not, that are in the Database with PID's it helps the NGS out a lot to have peole verify what is still there or not and how to find them may have changed. That is why they like having geocachers find them. The cost of doing it from the goverment end would be outrageous, and though these many benchmarks already did what they were needed to to for the NGS in their day, they are still useful to many agencies for many reasons. It is very beneficial to the public to have them and know where they are. Imagine you are a local surveyor and you need to establish TBM's (temporary benchmarks) and you know where you will need to do this. If you check the NGS database for the nearest benchmarks and find 3 nearby but one was recently recovered and re described by say, a geocacher, you can bet that is the best bet to use because it is the most recently found and described. It may even have a photo that help locate it. It saves time and effort, then all you have to do is set up over the mark, you know the elevation off the datasheet and begin to traverse into where the TBM needs set. As for other agency Marks, well those belong to those agencies and were set for reasons that were not part of the Coast & Geodetic Survey's mission. The USGS has different Missions than the NOAA/NGS and that is why the databases aren't and should not be intermingled. Hopefully this helps explain why there were so many Bench Marks in the first place, Why some are not in the Database at NGS, which Geocaching uses, Why fewer are used today, and how useful the ones that still exist still can be.
  13. Thanks To El Camino for pasting the Datum Info, that was cool! I know this thread is a little cold but here is some further food for thought. Some things we may know, or not. Another way of looking at datums is like this, as simple as it can be, and in truth it really isn't simple. Obviously we have the Earth. For horizontal and vertical measurements made on the Earth we have developed a reference standard surface level we call a Geoid. The Geoid is a hypothetical surface of the earth that coincides everywhere with mean sea level. This is not an average of peaks and valleys, this is as if everywhere on the globe, both under Mt. Everest and over Death Valley, Mean Sea Level is known. Think of it as having Mean Sea Level known in Oklahoma, even though there are no seas anywhere near. How we know where Mean Sea Level (MSL) is, is a matter of which Datum you choose. If you page through your GPS you will see there are many choices. For this discussion let's stick to three. NAD 27, NAD 83 and WGS84. Now a Datum is a set of parameters that is used to describe where Mean Sea Level is. Inherent in the problem is that the Earth is not a perfect sphere, it is ellipsoidal and it has bumps and undulations in it that change over time. So since the geoid is not spherical nor perfectly elipsical, the Datum can't be either. The geoid does not make it easy on the datum to describe it. If we could picture it in our heads we could imagine 3 one foot diameter globes meant to represent the earth as it actually is, but they each, in their attempt to be an exact replica, they fail just a little in their own ways, yet some offer more accuracy than others. All three a representation of Earth's Geoid. Each globe represents a Datum of the Geoid, such as NAD 83... From the Mathematical reference standard Geoid (the datum) we measure both distances from point to point on the geoid (MSL) with Lattitude and Longitude, distances which represent elevations as depth below or heights above the Datum. The total surface Mean Sea Level allows us to have a reference to measure from, it is where the world wide zero point is. The main things we need to know in a basic way are as follows. Test the Datums for yourself. Take your GPS and go to a point about a mile or so from where you are, make that spot a waypoint and come back. Maybe you can use a waypoint you already have. Now, check which Datum your GPS is set to and then set a Go To with your GPS to that waypoint and write down the bearing and distance. Then change to several other Datums and compare your bearing and distance to that place across the datums. The further the distance from you the waypoint is, the larger the error. You are where you are as far as the sattelite is concerned, but the datums are handling where that waypoint is in reference to you differently. You will see it makes a difference. Geocaching is a world wide activity. WGS 84 is usually the default Datum on most GPS and it is a Datum that works well anywhere in the world. You can take it from country to country and it works well, keeps things simple. I cannot reccomend using it for finding Benchmarks and it is unsuitable for reporting them. The NOAA/NGS, by way of being the C&GS, NOS NGS etc, Have developed their models of the Geoid as time has gone by. They did a good bit of the early body of work in NAD 27 and The Latter in NAD 83. This is what they prefer to use. NAD 83 is the Datum required when looking for and reporting Bench Marks to NGS Old Measurements are well, Old. It does not mean they are bad or cannot serve a purpose, But here is the problem. Not all earth is stable earth. Sometimes Earth moves via Tectonic activity, Disimilar soil type shifting, Hydrologic Forces, Earthquakes, Erosion, and Tampering, both intentional and unintentional. At the same time, The total database is very large. Yet many Bench Marks are missing or destroyed. How many old company watertanks and chimneys are now gone since the ending of the old industrial age? How has progress destoyed or buried some of the discs we have attempted to find? Buildings get remodeled. Did a road need repaved or a law that requred a wheelchair ramp in a sidewalk interfere with a Bench Mark? Many of those super tall Bench Mark/Landmarks (which were used for triangulation) are no longer with us, or are replaced with something new which is not the Bench Mark. Has anyone not noticed for many years until we noticed? Did the USPSQD not notice this Bench Mark change or discrepency from the window of their car as they drove by at 30mph? Then verified the the Mark "Good as Described" or "Not Found" after doing so? I know we all have found that Bench Mark before. (enough fun at their expense there) Of those that remain, they were monumented and that was likely the last time they may have had their position verified. They may have been found and had their condition and description reported but not measured. In addition, many of them have seem many things used to describe how to find them change, making some (as we well know) difficult to locate. The scaled and adjusted coordinates we see on the datasheets for older Bench Marks were often originally derived from NAD 27, were originally scaled with rules on a Map, and are often not good enough to walk us right to an older Bench Mark with a GPS. That is what the description was always for. When we find them and report them with a GPS fix and report that fix by noting what the gps says when we place the GPS directly on top of the bench mark and write that coordinate down, we enable the future Scientists, Engineers and all the other professionals who use them an update that allows them to use their GPS to walk right to that Bench Mark and Go right to work. When you use a map to help you locate a location, if it lists a Datum, Set your GPS to match the datum, then where you are on the ground will match the map. It helps! (really!) Many USGS Quadrangle Maps use the NAD 29 Datum, so when you find the Bench Mark, remember to switch back to NAD 83 for the Mark Position. And Finally, remember that the Map is not the territory, the GPS is not the territory, the description is not the territory, and well, the territory is not what you might have expected. But do be impressed and enjoy! Happy Bench Marking!
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