rusty0101
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Posts posted by rusty0101
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You will find Caches predominatly use north as the cache implementer perceives it. I suspect that this is predominately magnetic, however in places like alaska far western US and western Canada, you will probably find that they are using either true north, or adjusted magnetic north. (for any specific volume of area on the surface of the earth there is an average declination between true north and magnetic north. In Minneapolis MN, the declination is less than 10 degrees.) Since the Magnetic north poll is somewhere near the north end of Hudson bay, CA, there is a large segment of North America where Magnetic North points no where near North.
Benchmarks use True north. There are two observational ways to get true north, and several mechanical and electronic methods available. The easiest observational method, (though growing increasingly in-accurate) is to locate the North Star at night. (increasingly inacurate as earth's precession is moving the true north poll off of Polaris.)
The second method, though it takes longer, and provides less immediate precision, is to take a stick, or post, and mark where the end of the shadow of that stick is at some time in the morning, then again at some time in the afternoon. The line between those two points is extreamly close to true West-East. A line perpendicular to that line is a True North-South line. Regardless of where on the globe you are (asside from within the arctic and antarctic circles) the first mark will always be West, the second always East, and if you stand so the West is on your left, and east on your right, you are facing North.
I won't go into the mechanical and electronic methods, explaining how a gyroscopic compass, or laser compasses work may be fun, but gets to be a bit too much like work. Suffice it to say that once one of these has been set up to reference True North, it will provide you with a True North pointer as long as it has power.
For the purposes of finding either a cache or a benchmark, this is overkill. For the distances provided in benchmark descriptions, you are generally ok using a compass adjusted to within 5 degrees. This is not the case with orienteering, where you may have to use a compass to navigate several miles, and find a target to within 1 or 2 degrees, but in almost all cases, benchmarks, reference marks and described landmarks are all within 100 meters of each other.
Have fun.
-Rusty
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(amature warning, I don't do this professionally.)
CORS is related to dgps, but is not necesarily directly related. As noted near the top of the thread, a CORS continusously collects GPS information, at a fixed and well known location (at least amoung the users of the CORS data).
An example of a non surveying use would be providing navigation information around a small harbor. Prior to GPS being widely available most well traveled waterways were covered by a fixed location broadcasting system called LORAN. There would be several LORAN transmiters along the coast. A CORS station could (and very well may have) provide supplemental data to LORAN receivers to compensate for whatever inaccuracy was built into LORAN.
Another use of CORS is to provide a DGPS and possibly WAAS alternative for people with low end computer connected GPSr. If the software you use supports it, the software can pull down correction data from a CORS, and get a more accurate fix on your current location.
Of course by the time you add up the cost of the computer, the cellular packet bills and modem cost, and the GPSr you have attached to the computer, you could probably pay for a much higher grade GPSr which supports WAAS or even DGPS. But of course the computer is usefull for other activities, which the higher end GPSr may not be. (like word processing and providing updates to the geocaching website.)
I strongly suspect that some (though not all) of the CORS marks are providing the correction information that WAAS enabled GPSr are using to bring the accuracy of such devices from 120 meters down to 15 feet.
Then again that's just my feel for the situation. I have been known to be wrong in the past.
-Rusty
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First check would be to see if US Power Squadron has recoverd either mark in the past. If they have then I doubt that anyone would have a problem with you checking them as well.
Other considerations, where are they located that they require a manhole cover. If they are in the middle of the street, leave them alone. If they are in a sidewalk, or a median, you may be ok. Keep safety in mind. If there is a significant potential for injury, it probably is not worth it.
Also take into consideration the weight of a manhole cover. A standard 3 foot disk weighs in the neighborhood of 150 to 200 lb. If this is a 1 foot disk in a sidewalk, you may not need any extra tools. It is possible that you can lift it out with your fingers, but don't bet on it. It likely has sand or other grime helping to hold it in place.
-Rusty
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A couple of suggestions. While you can get highly precise GPS indications on data sheets, well over half the data sheets that I have worked with indicate the information is Scaled, and may be off by as much as 6 seconds of arc.
This is a bit more challenging than a GPS getting you to within 20 or 40 feet of a cache, and having to cast around for an orange 5 gallon pail with a lid on it marked geocaching. 6 seconds of arc is around 5-600 feet, and if the mark is a nail, good luck.
In almost all cases, it is better to use a GPS to confirm you are in the area of a benchmark, and use the description of the mark and it's suroundings to actually find the mark.
As noted elsewhere, just because you are not the first to find a mark doesn't change the thrill of finding it for yourself.
My own recomendation is to print off the first five marks closest to both home and work, then see what the experience is like either on a weekend, or for a bit of time preasure, during a lunch break.
If you have a favorite gas station between home and work, or use a bus or train station as part of your commute, get the gps coords for those locations, and pick a few marks around it, then look for them on the way to work, or on the way home.
Just a few ideas.
-Rusty
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Well, I'll bite, but only because I feel properly baited.
I will agree that a bridge abutment does seem unlikely to be a good point to be considered suitable for GPS readings. At the same time I have my doubts about it being a good spot for a "light" or other most other survey equipment.
My prime candidate is 2781AH with pid PP1048. I suspect that the railing to the immediate south of this mark would make it difficult to set a tripod to position directly over this mark. (the clipboard in the last picture is approx 9.5 inches wide, the water bottle another 4 inches perhaps, then the railing. I personally would not consider this a good candidate for a GPS reading for other reasons, such as the huricain fencing to the immediate north (this is the end of a foot bridge over I-94) and the high rise appartment complex across the street to the south. Both provide obstructions that reach above 15 degrees above the horizon.
Oh, if you haven't brought along a sextant, or even a protractor, string and nut to make a improvised sextant, you almost always have a field expedient way to measure 15 degrees above the horizon. This is not exact, by any means, but is often handy when you don't trust your watch, etc. If you hold your arm out, and bend your wrist so your palm is towards you, and the bottom of your hand/little finger is on the horizon, the top of your palm is approximately 15 degrees off the horizon. This makes a makeshift clock in that 15 degrees is 1/12 the the arc across the sky, meaning that if the sun is above your hand when placed this way, you can expect another hour of daylight at least. Two hands two hours. Beyond this things get flaky because your hand is not exactly 15 degrees at this distance, and so on. You can use this to estimate in 15 min increments (of time, not degrees) by counting the number of fingers the sun is above the horizon as well.
This is all rough estimating, but if you are out looking for benchmarks, and want to make a quick check to see if there are obstructions above 15 degrees off the horizon, over a significant portion of the horizon, it is a lot easier, and faster to stand at the benchmark, hold your hand out, and turn through a complete circle than it is to try to find a protractor in the bottom of the trunk.
-Rusty
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I don't know what faa regulations dictate it, but I think any airport that receives comercial traffic has to have either a beacon, or a ifr transmitter set to support that traffic. Commercial traffic is not limited to passenger traffic.
An example of a small airport that has both ifr equipment and a beacon is the Houston County airport just south of Caledonia, MN. (between pids ON1300 and ON1301) this is the fallback airport for FedEx to land at when the LaCrosse,
WI airport is fogged in.
I remember when the IFR equipment went in, and think that that it was put in specifically to support the requirements for FedEx to land there.
I found it strange that there were Fargo to Winnepeg Airway Beacons, as well as Chicago to Omaha, yet no listings of anything to or from Minneapolis or St. Paul airports. I would have expected all four of those cities to have connecting routes to Minneapolis or St. Paul. Perhaps they followed the railroads though.
-Rusty
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Bumping an old thread, but just picked up a Bushnel YardagePro at Sportmart yesterday for 179.97 plus tax. Depending on the target, it ranges out to 640 meters/700 yards, and is a laser rangefinder.
I may have gotten lucky on this purchase, there were two Bushnel rangefinders in the display case, one with what appeared to be two objective lens' with a center laser source, and a single eyepiece, and the other a monocular style with a single objective lens, additional laser lens, and a single eyepiece.
The box the rangefinder I picked up has a price tag on it reading both 389.99 and 299.99, but the salesman was unable to find any pricing information on the other rangefinder so rather than wait another 20 or 30 min (I was picking this up while waiting on going to a movie) we both agreed to the 179.97 on the tag being for this rangefinder. (the back of that tag did have something close to the 389.99 price, so I feel I did not rip them off)
I think I would have been happy with either, as the other provided feedback on the quality of the target being ranged.
As the accuracy is +/- 1 yard, I am not sure that it will be helpful on marks that are less than 50 yards from reference points, but I am very sure it will come in handy when measuring points across well used highways. If it can get me to within a couple of yards of a marker, I think I can handle the rest.
-Rusty
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You may want to search for tips on benchmark cleaning, as there are some general rules you may want to pay attention to.
Generally you should attempt to avoid using any caustic chemicals, or anything that will scratch the finish of the benchmark. Benchmarks nautrally develop a patina that actually protects the rest of the metal in the mark.
Examples of things to avoid doing include using Braso (or other brass polishing coumpounds) to make the mark shiny, using sand paper to remove thin layers of paint, or chisles wire brushes or knives to dig through multiple layers of paint.
When I find a mark that is painted over, I personally avoid trying to remove the paint. If the mark is otherwise as described, and I can see enough of the features of the mark to confirm the ID, I will use that information. Otherwise I would not log it.
If the paint is already flaking off, I may use a fingernail or soft brush to remove as much of the paint as possible. Otherwise if it won't come off with the water I carry in a squirt bottle, it's not worth damaging.
Looking over your pictures, all I can see that you have improved is that you can now read the word "surveyor", everything else was already readable. It looks like either doors, or bumpers have scraped off most of the information that would be of use already, so it does not appear that you have further damaged the mark.
-Rusty
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Another thing to take into consideration is that it takes a significant amount of time to make sub-centimeter measurements.
On top of that there is a bit of randomness between different pieces of equipment. One of the sigs you will read if you go through the forum points out that someone with a single GPS is never lost, someone with two GPSrs never knows where he is.
As a last point of note, any GPSr that I may happen to use, has nothing like the accuracy of a surveyors GPSr. If I take a data sheet and expect my GPSr to take me to that mark, I will be sorely disapointed. My display may report that I am within 12 feet of the mark, but that last 12 feet means a circle of diameter 24 feet, or about 80 square feet of area. (if I happen to be lucky)
-Rusty
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While I have not been on a base in the past couple of years, it was not unusual when I was in the military to see "photography prohibited" signs at various bases. It didn't stop the baracks rats from getting pictures of other baracks rats being drunk, or doing silly stuff.
In almost all cases, the reason that these signs, and various other similar signs exist is to protect against terrorists planning assults on the instalation.
A camera can be a very precice piece of surveying equipment, and photos taken prior to accidents where all parties to the accident were killed have been used to determine who was at fault. (In one case an accident where two helicopters colided, a picture taken by a tourist in the helecopter, of the ground was used to determine what height the helicopters were flying at, and which choper was out of his flight zone.)
Given all that, you may still find situations where the base rules may say in general it is ok to take pictures, but some areas are off limits. If you have permission to be on base to begin with, I strongly doubt that there will be anyone opposed to you finding a surveying device which is in publicly available databases.
If you ask the right people, you may even be invited to teach other retirees how to use GPSrs to find their way or as a way of being active and getting out.
As a further idea, you may be able to have a look at some of the military grade GPSr, that the soldiers on base may have available to them.
I do strongly recomend staying away from any physically dangerous locations, marks in the middle of streets and highways, or any place where you wonder about your own physical safety. No sense in falling down an embankment onto a freeway, or into a freezing river.
-Rusty
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It is not unusual to have multiple postings, both on markers that have been found, and on misses. One reason for this is that you may know something about the mark that the person before you does not know. You may want to post a clearer picture, or you may want to confirm that you made a best effort to find the mark and were not able to either.
It is also not unusual to find that a mark contains several components. One PID may include a transit station, a couple of reference marks, and an azimuth mark. Or more components. If you find the transit station, but decide not to go after the remaining marks, someone coming along after you may decide to take a couple extra hours to locate the rest of the markers.
Personally one of the things I like to do is read about personal observations about the mark. You may have chosen a day with bad weather, or decided to trudge out in some snow, and found marks that would have otherwise been no adventure at all. Or you may decide to see if there are any marks that might be interesting on a trip you are taking. I don't think that the fact that someone else has found the mark should in any way disuade you.
-Rusty
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39 feet comes to 11.3~ meters, 36 feet comes to 11 meters, 33 feet comes to 3 meters.
If the tracks are abandoned, or have never been upgraded to ribbon rail (each section being a little less than a kilometer in length) you should be able to count the physical rail sections to get close to the mark. A rail joint usually has a pair of splines, one on each side, bolted together with four bolts. If you can see the sides of the rail you should be able to spot the joints, and simply count them.
If you have a contractors tape measure, you may want to look for some abandoned track in the area to confirm what the local interpretation of a "rail" length is.
At 9 rails, I would start from about 85 meters going out to about 110 meters from the starting point. This should cover everything from 8.5 rails at 10 meters per rail through 9.5 rails at 11.3 meters per rail.
Again the best option would be if the original rails were in place. Then you count them, estimate back from the rail joints as necessary, and start looking in that area. Searching over a 15-20 meter range would be a bit more than I would like to take up as a challenge.
-Rusty
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... on private property. If you do not feel comfortable asking the property owner for access, don't try to recover the mark. We are not BASE jumpers.
Additionally, the people in larger buildings, who can physically provide access, are rarely the people who can make the decision to provide that same access.
If you are interested in getting to some of these marks, I would recomend contacting property management for the building. If the building has a Conciearg, this person may be able to provide you the contact information. If the building has a security desk at the entrance, it is likely that finding out who to contact will be harder.
If the NGS data sheet does not have a point of contact for the building, that is a reasonable enough explanation for people to provide an update to the NGS.
If all you are going to do with your benchmark recovery is log it here, then I agree with the notes earlier that these marks probably are not worth the trouble.
As a rule the surveyors working in an area with buildings that have benchmarks affixed to their roof (as opposed to a flagpole or spire being the mark itself) will have their own set of data and contact information for these marks.
That said, if a mark has not been recovered for a couple of decades, it is reasonable to expect that some of the contact information has changed, that the roof has been re-surfaced, and that there may be other changes that make it a good idea to collect what information you can to update the NGS datasheet.
If for some reason a survey crew who is not from the area needs to use that mark, the updated contact information on it's own may save the surveyor several hours or even days of independent research to collect that same information.
Then again, that's just my opinion. As has been noted elsewhere, with modern surveying methods, and current GPS tools, it is likely that in the future there will be much less of a need to occupy any one specific point. A large building, with visability for miles around is quite nice, but hardly required.
-Rusty
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... for hitting all of within my county. There is only 88 in the county I live in. That should be a good target for this summer. Unless I move first...
-Rusty
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whenever possible, provide whatever supporting information you can for benchmarks that are destroyed. A photo of the area is often helpful.
A better bet is to check with local authorities for information on when the mark was destroyed. If the mark was a church steeple, smoke stack, or water tower, there is almost always someone around who remembers it being brought down.
Bench mark disks on the other hand may have simply been paved over, or may have a burried component that will allow the mark to be relocated at some time in the future should that be of interest to the NGS or local surveyors.
If you read through the descriptions of enough finds, or even in this forum, you will find markers that were "not found" for many years, then found by someone who dug down 6 to 12 inches. This is part of why the NGS wants evidence of a marker being destroyed whenever possible. They very often want the marker disk itself if at all possible.
That's my opinion at least, some of the real professionals may have other opinions.
-Rusty
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to be four meters. 4 meters is about 12-13 feet. He is also only checking lateral varience not vertical. Theoretically the lateral (lat and lon) measurements should not change by lifting a GPSr from the surface of a marker too several miles vertically over the marker. It should definatly not change so long as the marker is vertically under the GPS within the range that a person can hold it above the mark.
4 meters is acceptably close to a mark for a non waas enabled GPSr, with waas it should be within 3 meters, though with a benchmark established during a different datum, it would depend upon how well the transformations required to convert the datum information was done.
-Rusty
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I just posted a witness post for AE8944, (have yet to find the marker itself though, will have to wait for some snow melt) I have also posted a couple of witness posts for ON0783. None of those are ledgible in the pictures though. At the same time they can give a sense of what to look for in the ditches and along the highways.
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With what passes for warm weather today, I hit up seven of the 50 or so markers within 2 miles, found three, didn't find three. One looks like it has been paved over, two I couldn't find because of the snow. I will revisit the two that look findable because of snow later this month. One of the seven I believe is destroyed, too much new construction over the past couple of years.
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... just enter zip code 55406 into the search form, and
wait...
just a bit more...
Yes, your browser is still working...
It's only about 1000 markers. Most of them ready for the picking. With the temps comming up over the next week I may even be able to pluck a few.
-Rusty
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The only two situations where I consider documenting a benchmark as destroyed are when the benchmark was a building or spire that I know was destroyed, see ON0788 or when the benchmark shows obvious damage. If it is a disk on a concrete block, and it looks like someone took a sledge hammer to the block, ON0783
Even then, claiming that the mark is actually destroyed takes a bit more proof than the pictures I submitted. I actually went back and took pictures of the block with a level to show that the block itself appears to have been disturbed. (I show an edge that should be either vertical or possibly canted towards the center of the block, having what appears to be a 15-25 degree angle overhang.
Every situation is a little different. Take your time and have fun.
-Rusty
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Good picture.
Purely as conjecture, I think that a magnetic station disk would be used for one of two things. Either this is a place where a surveyor has calculated a specific magnetic north bering compared to a polar north, and can be re-used as a reference as magnetic north shifts around, or this benchmark is used as a local reference for a magnetic anomally in the area. One of the pros around here may be able to give you a better bit of information.
In places wher there is a high concentration of Iron, Nickel, or other magnetic metal, it is not unusual to find that the local North varies from standard Magnetic North. This is one of several reasons that Magnetic North is not used by surveyors.
The top of the IDS building in Mpls has five benchmarks alone. Two building corner beacons, Two tower beacons (one of which is currently inoperable), and a benchmark in the center of the roof. Since I don't have approval to walk around on the roof, I don't think it would be right to claim the last mark.
As local construction changed the landscape, or skyline, benchmarks were added for usefulness. Also as different types of projects were started or in progress, different types of benchmarks were installed.
Look through the message history and you will even find benchmarks that were physically placed on top of each other.
Have a good time.
-Rusty
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After looking at the picture, you might want to try going back to this mark in the summer. I do not see anything that is obviously holding this down as a fastener. That suggest that the reason you are not able to open the cap is that the cap is colder than the pipe the cap is on.
It probably takes some effort to get the cap off of the pipe in the summer, but when the cap shrinks during the winter, it gets a lot harder to take off. The pipe goes several feet into the ground, which is usually somewhat warmer than the air above the ground where the cap is.
Have fun.
-Rusty
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quote:
Originally posted by Orygun-Connie:We have found two benchmarks now, but neither are on the list of benchmarks. I'm new to this so would like to know what I do now. I would like to mark these as finds, and am not sure how. The one we found today is at N33 17.577 W111 26.528
orygun-connie
As of the last I read, benchmarks that are not listed in the NGS database were not availble to mark as found in the GeoCache or NGS systems. GeoCache listings are pulled from the NGS database, meaning that if you find a benchmark that is not listed in the GeoCache database, it has not been reported to the NGS by the people who placed it there. This may be for a number of reasons. Including the posibility that the people who placed the mark you have found having no relationship with the NGS.
GPS readings of benchmarks are not always useful. If you read the descriptions of some of the marks in the database, they will point out that the mark may be as much as 6" of arc from the co-ordinates provided. On top of the inherent inaccuracy that the GPS itself will inform you of, (usually no less than 15', this 6" (not inches, seconds of arc) can place the mark you have found anywhere within a 600' (foot) radius of the co-ordinates you provided. That's quite a bit of ground.
I think I have recomended to others in the past to keep track of any benchmarks you find that are not listed in the database. How you format this database will be your own prefernce. You may want to use a datasheet from the NGS database, or even the GeoCache website as a template for your own database. Or you may want to simply keep track of things on 3x5 cards. It's up to you.
At some time in the future there may be a way to add entries to the database. When that happens, having a database of your own to work from will simplify adding your finds.
Good Hunting.
-Rusty
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quote:
Originally posted by HoosierDuke:Went benchmark hunting this weekend, and at the location of one of the benchmarks I was in search of I found the 6" PVC tube with cover as seen in the PDF under another topic. My question is, is it proper (or even legal) to remove the lid in order take a picture of the benchmark? If so, what is the easiest/proper method for removing the top? I made a half-hearted attempt with my hands to remove the lid to no avail.
On a side note, I did find my first "verifiable" benchmark this weekend ... complete with a sign stating that the mark was nearby (btw, is this what is considered a "witness post")?
first of all, congratulations on the find. The sign indicating that there is a benchmark close by is one of several varients of a witness post. Some Witness posts are simply a sign post driven to stick up 1-3 feet above ground with no markers of any type on the post.
It is unlikely that the cap on the PVC pipe has been Fastened to the pipe, as surveyors will need to access the inside of the pipe to use the benchmark. If you see threading, you should be able to turn the cap off, though if the cap is a hex nut type, you may need a tool. At that point I would let it go as you have the potential of disrupting the PVC and cap to the point where you damage the mark, or defeat the reason that the cap is there in the first place.
At that point I would do my best to confirm that the PVC pipe is where the benchmark is described as being, relative to the reference marks, and identify it as found in the benchmark records here, with comments re the cover being difficult to remove to the point you did not open it to see the benchmark itself. I would not register it as found at the NGS, but that is my opinion.
Others may give you different advice.
-Rusty
New at benchmarking, but what did I find?
in Benchmarking
Posted
I am not absolutely certian based upon your description, but it is unlikely to be in the ngs database.
I would tend to suspect that this is a triangulation point of some sort. Most elevation markers will at least be stamped with the elevation of the mark. While you may not remember, were both lines of the '+' the same length, or was one line longer, looking more like a '-+-'?
If so, you may be looking at a reference mark or azimuth mark for another marker. If this is an azimuth mark, I would look along the longer bearing line some distance for the actual mark. If you captured the GPS coordinates for this mark, you may want to look in the database for the nearest mark, and see if there are any notes regarding an azimuth mark in any direction.
Again, these are usually stamped with some sort of identifier. So the fact that it is not would suggest that it was installed by a local surveyor for his own purposes. In that case the "+" that is marked on the disk is something that he is using for his own purposes as well.
You may want to look through DustyJacket's photos of benchmarks and see if anything there looks familiar. There are also several other resources online, a few pointed to in other threads that provide information that may be useful.
Enjoy. Here's hopping Benchmark hunting gets you as hooked as geocaching has. You might find yourself tossing a quick search for local benchmarks to geocaches you have been to or would like to visit, as an added challenge.
Have fun.
-Rusty