# jwahl

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2. ## Question about Data Sheet Description

The mistake in the datasheet description I see is that it should be ABOUT 125 YARDS SOUTHEAST OF THE SOUTHEAST END OF THE NORTHWEST TANGENT OF CURVE instead of Northwest. It isn't that easy to specifically identify the tangent point of the curve to much better than 35 feet or so. The other calls then to the road and trail as well as to being on a large rock and using the topo coordinates should be okay. If you use the 125 yards that moves it NW along the road from where the topo sheet puts it so you have a few hundred feet to search along.
3. ## Tienstra's Formula Revisited

I assume your calculator is using plane coordinates. Thus you could input UTM values, or State Plane Coordinate values. In either case those are on a projection and for a large figure grid angles are not equal to the geodetic angles you would get if you were actually on the point turning them. The turned angles can be corrected to grid by means of computing a thing called the T-t correction, however an approximate calculation of the position would have to be made to compute the correction, followed by small changes in the angles. Anyway using SPC coordinates for the GC1B0Q9 resection problem the solution using plane coordinates is within a few 1/100's of a foot of the correct solution. When considering that the angles are given to 0.00005 of a degree which amounts to 0.2 seconds the solution has inherent error of a few tenths of a foot anyway. Thus the error in using uncorrected grid is pretty small in this case. - jlw
4. ## US General Land Office Survey Makers

I am not from Las Cruces, but I can provide some clues. The GLO or General Land Office were surveyors for the Federal Government up until 1946 when they merged it's operations into what became the Bureau of Land Management. Between 1908 and 1946 the monuments they set were brass caps on 1, 2.5 or 3 inch iron posts. Usually the monument would be to mark a section or 1/4 section corner, but the GLO also surveyed Indian reservations, and all kinds of grants and claims. So what you found would likely be either a PLSS monument (PLSS stands for Public Land Survey System), or a corner of a grant. It should have marks on it which give it's designation. Plotting the location on USGS quad source will probably give you a good idea. The actual survey records which describe the monument would be located at the BLM office in Santa Fe. Some of their records are being scanned and put on the internet, but the work is just beginning. There will be a plat which shows that parcels being surveyed and the bearings and distances of the lines, and there will be a set of field notes which describe the survey and each monument and how it was established, marked and referenced. Some NM plats are on line here: http://www.glorecords.blm.gov and perform a survey search. You have to already know the approximate location by township and range which is probably 23S 1E of the NMPM. Tell us the lat long and maybe we can help. - jl wahl
5. ## define "BOLT"

This might be an example of a situation where one more investigative tool could help. That is determining the actual elevation of the candidate mark. I know that is beyond the capability of most on here, but it is still one critical element of information that can be added after all the history and on the ground investigations. As an aside relating to an earlier post. The difference between the older '29 datum and the current datum can be computed with an NGS program called VERTCON. That may not be exact since it is an interpolated model. The best solution is usually to compare the two published elevations on a mark in the area. - jlw
6. ## Bearing Trees

I would not expect it to be very common to have a Bearing Tree for a benchmark. Occasionally horizontal control stations have a marked tree. Most often bearing trees are associated with property corners and in the west it was and is extremely common to have bearing trees on PLSS corners. (Section and 1/4 section corners.) So I suspect what you found was a BLM or GLO section corner and possibly on a USFS boundary where they often set signs. jlw
7. ## "Suitable for Satellite Observation?" Maybe not....

Your problem may have been made worse by a weak or poor configuration of satellites. That is the number and location. I think survey grade receivers have more capability to filter out multipath by only using the first signal received for example. However it wouldn't hurt to pass on the information such as 'Location suitable for Satellite observations. 'Large metal barn roof nearby may create multipath issues.' or 'iron bridge structure overhade may create multipath problems'. Those things in particularly if they are not obvious in the aerial coverage could save a surveyor some wasted time. - jlw
8. ## The Epping Base Net of the Eastern Oblique Arc

There is a Scott Zelenak who posts over on rpls.com and is a surveyor who works for the NY Port Authority. - jlw
9. ## NGS benchmark recovered

Here is another possibility farther west: National Geodetic Survey, Retrieval Date = DECEMBER 2, 2008 CZ1849 *********************************************************************** CZ1849 DESIGNATION - CWA 2 CZ1849 PID - CZ1849 CZ1849 STATE/COUNTY- AZ/PIMA CZ1849 USGS QUAD - TUCSON (1992) CZ1849 CZ1849 *CURRENT SURVEY CONTROL CZ1849 ___________________________________________________________________ CZ1849* NAD 83(1992)- 32 08 41.14430(N) 110 57 09.48957(W) ADJUSTED CZ1849* NAVD 88 - 776. (meters) 2546. (feet) SCALED CZ1849 ___________________________________________________________________ CZ1849 LAPLACE CORR- 2.26 (seconds) DEFLEC99 CZ1849 GEOID HEIGHT- -29.36 (meters) GEOID03 CZ1849 HORZ ORDER - SECOND Note that RM 3 is quite a ways away from the station. Based on a quick computation from the above station, the Azimuth mark which they are also calling RM3 seems to fall in a park between a couple of baseball or softball fields. Does any of that fit? If not, it helps others help you if you give the position where you found the thing and the picture, etc. Also the whole discussion should probably move over to the benchmarking topic. - jlw
10. ## Correct Term for Disk's Observed Point?

I saw the term 'datum point' used in a diagram from the NGS bluebooking documentation. I have not seen it used widely in surveying, but it would seem to be a term NGS has used for some purposes. - jlw
11. ## Laser Rangefinder

Leica Disto is I think a brand that is marketed to surveyors. Things you should look at besides range, are accuracy. Also I am pretty sure, but not positive, that none of these gadgets will correct a slope measurement to a horizontal measurement, which is what most lines in surveys are reported in. So you would also need some kind of reasonably accurate clinometer and maybe an inexpensive scientific calculator to reduce the measured distance to horizontal.. There are a wide variety on ebay at any one given time. Reflective tape will probably help considerably and is a lot less expensive that a retro prism for hard shots. - jlw
12. ## Monadnock - A most unique station marker

Isn't it interesting though that RM1 and RM2 are almost on line with two stations?

14. ## Section Marker a Mile Off?

My best guess, is that someone did a survey and made up several monuments off site, hauled them up there to be set and someone made a mistake in which one they were setting. One needs to looks at where the proper corner appears to be to see if there is a similar type there. Also you could check with the local government agencies to see if they have commissioned a survey or have a copy of it. In CA surveys are usually recorded and the surveyor's license number might be on the monument somewhere. You might be able to find a copy of the survey in the county courthouse. - jlw
15. ## Does this one meet the qualification for destroyed?

As a surveyor, given sparse control in that area, I would not hesitate to use it after verifying the RM for horizontal work, and rough vertical I could estimate the height of the cap above the bedrock and be good enough for many purposes. I did work in the general area (Tuba city and East) in the 1980 era. Before GPS, this kind of thing would be a blessing to tie work into. That probably means nothing in regards to the official definitions of desroyed, however. - jlw
16. ## Boston N. Shore Isl. Mark Hunt on Sat., Anyone?

From Google and the topo maps it looks like it might be in a cemetery.... On second look, it looks like the fenced part of the cemetery is to the north. The objects in the road turn around the hilltop may be boulders. - jlw
17. ## "Lost" Station from 1849 ?

I would suspect that some stations in the older networks were not brought forward into later adjustments due to an evaluation of the quality of the measurements, or specific decisions based on the monumentation quality. Mostly the former. Many stations in the original North American Datum were not published in NAD27 and a significant number of stations in NAD27 were not included in NAD83. Theoretically they all still have observations to them and station data, but it must have not been of sufficient quality to merit inclusion on the later work. - jlw
18. ## What's the mark for these five towers?

I do think that the description is confusing, but it seems clear from tower 5 that the position was 'traversed to'. What is unclear or unknown is how this point on the ground was determined and if it was monumented, there is nothing mentioned. Besides the string intersection idea, if I were a surveying it and wanted to be sure I had a point directly under the tower, I would establish that point either with a zenith plumet (something any C&GS crew would have for plumbing towers), or by simply sighting the tower from a couple of nearby transit setups and dropping line down from the center of the tower to the ground and setting a point. The first thought I had though was if there was something in the tower structure itself, that was visible and near the ground, such as some symmetry in the structure, cross braces, etc. Nothing is that apparent though from the photos. Of course "Center of the base" does not necessarily imply directly below the top of the tower. There not being any called for monument, it would be hard to assert having found it without qualification. - jlw
19. ## OK GC Jury, Is This One "Destroyed" ?

MS Livesearch oblique My interpretation is somewhere on the top. Perhaps one end of the outcrop seems more like a base or low end of the outcrop, but the top is in the cross section. I would search all of the top surface area, particularly any and all horizontal areas.
20. ## Old topo maps

There are two links that I am aware of for historic quads: First: Maptech and then Univ. New Hampshire jlw
21. ## Help with Eccentrics

There are two sites for historic quads that I am aware of. I think they have the same maps though: Maptech Historic Quads This was the original source: Univ. NH Historic Quads - jlw
22. ## Help with Eccentrics

An eccentric could be a target or a light sighted from other stations. I would check out if the 'lookout tree' or items setup on the tree. ECC 4704 is 19.180 meters or 62.92 feet away in a SW'ly direction from the station. The description says that the sation is 63 feet NE of the lookout tree. That seems like a pretty close match. The other eccentric is very nearly the same direction and about 4 feet different in distance. That seems consistent with two objects possibly on the tree or on the platform on the tree, or on opposite sides of the tree. - jlw
23. ## Need Surveyor Help, Please!

Good deal. So how does the location you had previous fit a distance pulled from RM2?
24. ## Adjustment of locations (tri-stations) over the years

I think you should give Dave D. a nudge - jlw
25. ## Need Surveyor Help, Please!

The location shown in your photo looks like about 6 feet or less from the curb stones, and if we were to believe in the positions shown in the plots earlier in this thread, it sure seems like it should be further SW by maybe 5 or so feet. How well did you position fit the ties to the original structure. Aerial photos are not perfect by any degree, but it makes me wonder. - jlw
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