Bill93

>If Mapsource was designed for what you are trying to accomplish with it, it would not be free. It would cost tens of thousands of dollars. My main point was that my $300 GPS receiver does the "correct" thing within the resolution of its interface, but MapSource from the same company does not. I'll have to try Holograph's test next time I can sit and think deeply about it. I was working with 45, 135, 225, and 315 degrees, which might increase the discrepancy over cardinal directions since both lines are "bent" between models. You used UTM, which I've mostly ignored to date. Maybe it is time for me to study UTM.

For Groundspeak only, you could probably claim destroyed with a clear conscience if you got your facts from good sources. You need better evidence if you are interested in reporting to NGS. Location is ADJUSTED. That means more accurate than your handheld GPS. Two sets of measurements posted for the present tower agree within 80 feet and both are almost 500 feet from the adjusted coordinates, which lie back up the road to the NE from the locations given in the logs. This says the new tower was not built on the old location. If you are in the area, go back and find the exact spot indicated by your GPS for the official coordinates. If you go back on different days you could get some averaging to improve accuracy. If you can see some sky, you might be within 10's of feet and average to better than that. Look in that vicinity for evidence there has been a tower.

I wasn't using its distance and bearing displays, which are rounded off pretty coarsely in both MapSource and the GPS. I set waypoints for the ends of the lines and ran a criss-cross route through those waypoints. I compared the crossing point as displayed with waypoints set for the flat-map solution and the ellipsoid solution. The GPS gave me a match within the resolution you can enter waypoints. MapSource does not. The GPS does a better job of plotting routes along the great circle. The file with longer lines can be found at Az315.gdb. It has waypoints along a 315 degree geodetic azimuth from an origin P0 to points 10, 20, 40, and 80 km distant, and waypoints for the flat-map midpoints of the 0-to-20 km lines, etc. For instance, the line for route P0 to P20 misses both waypoint P10 and FlatMidPt0_20.

I got interested in how calculations are done on the ellipsoid, partly as a result of finding MH0702 and trying to check the azimuth given in the description to confirm that there was a discrepancy in the coordinates. (There, I'm on topic for benchmarking). I found something I thought interesting while applying my new knowledge to the geocache Hot Crossed Lines. To summarize, it is located at the intersection of two lines defined by points that you go out and measure coordinates for. The person who hid it used a flat-map approximation to solve for the cache location and provides a spreadsheet in his hints to help those less mathematically inclined. I am far from expert at this yet, but I used the NGS programs INVERSE and FORWARD to get points on the connecting lines and determined that the intersection found this way is 23 feet north of the solution found by the flat map equations. Ok, that makes sense. What was really surprising was that Garmin's MapSource program gives a different answer than their GPS units. Using a GPSmap76s or an etrex Venture, a route between those points crosses within 0.00001 degree of the anser from the NGS equations, but MapSource is closer to the flat map answer. I then tried an example with longer lines and find that MapSource doesn't quite give either the geodetic answer nor the flat map answer. Has anybody else played with this kind of thing using their GPS unit or mapping programs?

Photos are nice but not required. You can only log it for the game score if it is already in the Groundspeak data base. You can look for it by approximate coordinates or the designation stamped on it using the benchmark search window. Some people also log worthwhile information to the NGS as a public service (no scoring). If you get interested in that after you have found a dozen or so, read up on the threads here that relate to it to learn about their criteria and practices. There are thousands of marks set by various agencies that are not in that data base, nor in many cases in any data base available on-line. Read the FAQ at http://www.geocaching.com/mark for more details.

I'm surprised at the outcome of the lake front case. I thought that if you had good title to a piece of land, acquiescence or adverse possession would apply to fix the boundaries after 50 years. Not that I'm a lawyer.

If you are trying to get the ultimate resolution out of your unit and will be doing averaging on it, use the decimal degree option. I think most of the units offer the same options. Degrees to 5 decimals is finer than minutes to 3 decimals, which is in turn finer than seconds to 1 decimal. I wish there was an option to get any of these with one more digit, even though that digit is very questionable without averaging. As for property corners, whatever you do don't disturb the evidence on the ground. The best plan would be to hire a local surveyor to find your corners and re-mark them as needed. If there is a decaying stake out there, you could ruin his best evidence while digging around looking for it. A local professional would know what was used in the area and may have resources you don't know about, such as records of other surveys in the area and ties to objects (trees and stones?) that you don't know are significant.

Another one for Roger's list: MH0702 has adjusted coordinates listed, but my handheld and a topo map both put those about 0.6 mile from where I found the disk. It isn't a slipped digit because the coordinates are southwesterly of the mark. I think it is likely those are the coordinates of another point in the same traverse, and therefore would have the wrong elevation also. I've submitted this information and pictures to Cheryl. There is also the discrepancy of changing distance between two nearby marks that we noted in a discussion of MZ1556 Peaked Mountain and MZ1557 Peaked MT 2. This was acknowledged by DaveD near the bottom of the thread. I've got some routine destroyed intersection stations reported and pending also, but I don't think Roger is counting those.

It is interesting that KV4107 the flagpole at Union City's City Hall has coordinates about 180 feet away from those of KV4106. How does that compare to what you see?

We don't know yet that the other person was smarter. They didn't give us a detailed enough report to prove that. And they have only been registered for 3 months. and this was about the 12th benchmark (as opposed to towers etc) they had found. >stubby metal painted over rod That could be the shaft the disk used to be attached to, if someone pried the disk off. "Marker Type: NGS Benchmark" would lead me to expect disks had been originally set, not re-rods. I'd go back and check every part of the description. Is each thing there? Maybe not everything will be as it was in 1975, but often you can tell that a street has been re-worked or a building added on to. Does the distance seem right after making such allowances? At my first reading, I would think the marks should be visible on the outside of the building unless they have enclosed a larger area since 1975. It would be possible a new lobby put one inside next to the the gift shop, but certainly not both of them. AT THE ALASKA RAILROAD STATION, 20.5 FEET NORTH OF THE NORTH CURB OF THE AVENUE Has the avenue been widened? Is 20.5 feet north of the curb at the window sill or inside? , IN THE TOP OF THE CENTER OF THE CONCRETE WINDOW SILL OF THE 6TH WINDOW WEST OF THE SOUTHEAST CORNER OF THE STATION BUILDING, That's pretty specific. 75.2 FEET WEST OF THE SOUTHEAST CORNER OF THE BUILDING, Also specific. Do these two descriptions seem to be consistent with each other? 8 FEET NORTHEAST OF A TOTEM POLE, Is it still there? AND ABOUT 3 1/2 FEET HIGHER THAN THE AVENUE Yes? And what do you see in the vicinity of the gift shop? Disks in window sills? Did somebody move the disks to a new place? Did the other reporter find some other kind of metal disk and mistake it for a benchmark?

With what look like screws around it, I'm betting it is a cover for something rather than being set to be a survey mark. I'm surprised you got that picture of a Federal building without any hassle. See how touchy they were here: MG0631 Fed Courthouse

On the subject of benchmarks, do you know what agency's name is on the mark pictured? What structure surrounded the mark and was supported at one time by the other blocks of concrete?

I really like the NGS flag idea. But with either separate forums or the flagging system, it is going to be difficult for us to keep a thread on topic. Just look at the history. So it would be best if the flag were clearable from the NGS end, and we could set it again if new relevant info or questions came up on the thread. That way when the relevant question, like "is there a mistake on this data sheet?" had been addressed and the discussion wandered off into another nearby mark that reminded somebody of the time ..., then the NGS flag wouldn't be wasting Dave and Casey's time. But if someone said "I remeasured it and know which distance is wrong" they could set the flag again.

They forgot to mention the call to the utility locator service. "Yeah, I want to pound a stake for my benchmark. No, I'm not a surveyor, this is just a game." Do they have any warnings about the risks?

I've heard that NGS has a few just across US borders into Canada and Mexico, but I've not heard anything to suggest they listed anything more distant.

Overall, I dislike it but don't see that it causes any serious problems. "Official" is a little strong here, just as it is too strong on junk mail. "Benchmark" is wrong because most of these won't have any survey data associated with them in anybody's data base. They won't be benchmarks. Basically they are another game token like a geocache. The copycat look was not necessary for that and I resent it. On the plus side, harder for anyone to run off with than a cache and provides another game. On the negative side, 1) not as interesting to many gameplaying folks as caches, 2) of almost no interest to technical type BM hunters, 3) tough to get permission to mount them most places that are easily accessible by the public, 4) confusion by new hunters over the distinction between these and agency BM's. I'll boycott them.

>>not in any data base There are lots of government agencies with data bases that aren't on the web. In this case the disk belongs to Los Angeles Co. If anybody wants to pursue the story, they should start by double-checking the coordinates in the NGS list for nearby active and destroyed marks. If no hits there, contact the LA Co. engineering department to tell them what you found. Its designation seems to be SAN PEDRO HILLS ??4 in the same series as DY2861. I am straining to read the lettering in the picture. If so, it doesn't seem to be one that was included in the NGS data base, and that wouldn't be surprising at all since there are thousands to zillions of marks that weren't worked up for NGS purposes, but do serve purposes for somebody else. I think the RE2177 is the license number of the Registered Engineer who set the marks, and appears both on DY2861 and the one near the water.

What do you mean "can be considered available"? If you've followed this discussion, you know that a mark is never available for the taking without permission, no matter what condition you find it in.

If the unit locks on the satellites, then it's going to give the best it can with current reception conditions within a few minutes, regardless of what it started out with. Re-initializing may have an effect as noted on initial acquisition in a new area, but I can't see any reason it would help otherwise. Once it locks on the satellites it is doing far better than any hints you can give it. If you change the time zone setting, it will display time for a different zone, but that doesn't affect its knowledge of precise time internally. It effectively knows UTC at Greenwich regardless of which zone you display. If time is 'way off when you turn it on it will take longer to find the satellites. But when the unit is tracking several satellites, it knows time to within a few nanoseconds. The speed of light is roughly 1 nsec per foot, so you can see how time accuracy is essential for position accuracy. Much better time accuracy than you can manually set. There is another multiplying factor depending on the angles to the satellites, but we don't need to go into that.

Be sure to convert to NAD83 in dd mm ss.s format for NGS submittal. Your area picture is decent. If you have a photo editing program, consider putting an arrow in there pointing at the disk. My pictures don't come out great, but here's an example of how I often do it. The arrow is really a text vertical bar that is stretched to fit. MH0702

It is ironic that this very famous control point was disturbed and required the best efforts of CGS to salvage. Read the 1948 description at MEADES RANCH RESET. Despite its fame, it is not publicly accessible. I'm also surprised that there aren't any others close by (nearby mark search).

NGS is collecting pictures, as discussed in the pinned thread at the top of the forum page. Cheryl Malone has replied to some of my submissions thanking me for them. They don't have many on line yet, mainly ones associated with particular projects. For an example see the NGS data sheet for GA2360. The third picture illustrates a GPS setup in a difficult position like Kewaneh was talking about.

Very few people who use the marks outside of NGS or USGS seem to report them. I have only found a few reported by other professionals. Time is money and reporting doesn't bring in any revenue. I know some of them do get used for non-government purposes. Rob has noted that he uses them. I've seen orange paint and flagging tape at some that had no recent recovery reports. In some cases, the local users have at some time transferred elevations to other more convenient structures and re-use those more often. For instance, they are going to build a retirement complex on the empty lot at the end of my street. I chatted with a couple guys from the engineering company when they were finding property corners. They said they would base their work on two known elevations, neither of which were agency marks. One of them was "on one of those power line towers over there", which a different local company had once measured relative to an NGS mark a mile or so further away. I couldn't find any disk, nail, chiseled mark, or orange paint on either of the closest two tower bases, so I'll recheck after construction starts. Don't know about your mark in question, but I suspect that a great many of them out in the boonies haven't been convenient to anybody and thus haven't been used in decades, maybe even since the great elevation measurement projects of the 1930's.

The letter-number series marks, to the best I've been able to figure out, were begun in the 1930's when there was a big push to do triangulation and leveling across the country. The letter-number ones were almost exclusively for leveling, and the triangulation stations used names taken from nearby towns, mountains, property owners, an whatever was on the crew's minds when they ran out of better ideas. There is a thread not too old on here about interesting names used for triangulation stations. A crew out setting marks for elevation leveling used one numbered set at a time in alphabetical order as they traveled a good route. A good route was most often along a railroad since that was graded to minimize hills and valleys and mostly cleared of brush, and both features simplified the work of getting good sights. In some places they also used roads. When they came to a town they often set one or more at the water tank, the city hall, or other prominent building. The numbers were re-used in different states, so you will find several marks in the data base having the same Designation. That makes the PID system important to keep track of who is who. They continued to use this letter-number form, and I have seen some of the new rod and sleeve marks with this kind of designator, such as AE9191 designation V183 set in 1997.

Worked ok for me tonight.