Always wanting to be completely fair in every respect, I spent a little time looking through old projects to find one where grid North as determined by hour angle observations on the Sun had later turned out to be grossly erroneous. I think I found one example.
This is a cut-off line that ran for nearly three miles across a ranch. I marked each corner of the line with a "+" on a brass tablets set in concrete, so there wasn't much doubt about the location of the corner on the ground when I came back with GPS about 13 years later to resurvey the boundary.
[pre]
Per 1992 Survey
Grid Brg. Grid Dist.
100-101 S2°01'02"E, 5237.95 ft.
101-102 S10°22'40"W, 1744.54 ft.
102-104 S1°46'01"E, 8751.40 ft.
[/pre]
The grid distances from the 1992 survey have been corrected by -4ppm to reduce them from the geoid to the ellipsoid, and so that they are at the same nominal scale as the 2005 work which was computed in the Texas Coordinate System of 1983.
[pre]
Per 2005 Resurvey
Grid Brg. Grid Dist.
100-101 S2°01'01"E, 5237.97 ft.
101-102 S10°22'38"W, 1744.56 ft.
102-104 S1°46'02"E, 8751.24 ft.
[/pre]
That discrepancy of 0.16 ft. in the length of the 8751.24 ft line was actually the result of the survey design and the connections from 102 to 104 being relative indirect, running from 102 to a control point on a hill about 8100 ft. NE and then SW about 17,500 ft. to a control point about 3800 ft. West of 104 and then to 104, instead of directly to 104 which could not be done easily conventionally within the practical constraints of the project.
However, as may be seen, the grid bearing from 101 to 102 as derived in 1992 from solar observations turned out to be in error by 2 arc seconds, which amounted to a major error in the 1744.56 ft. line from 101 to 102. I'm nearly certain that bearing error wouldn't work in New Hampshire.
Kent,
are you being serious in this post?
Grossly erroneous? 2 arc seconds? A discrepancy of 0.16' in 8,751.24'?
Last week I had a 1,603' shot between two traverse stations, direct observations distorted by heat waves on a private grass airstrip, that differed by 0.03 horz., and 0.15' vert., that I called good enough for topo.
That shot was the longest direct observation that I have had.
Jim
This recent debate reminds me well of a lesson I learned from an old engineer many years ago. I was a young project engineer given responsible charge of a flood control project through the heart of a small city. I'm having a beer with my old mentor discussing the city's project and some guy butts in and wants to give me his "perspective".
As I start to argue some of the project's objectives with this slightly buzzed layperson, my old friend turns to me and tells me that you can't win a debate with the chronic ignorant. No matter how right you are.
Don't let the ignorant drag you into a pointless debate. Best to say your piece and leave it be than to let educating the uneducatable consume you.
> are you being serious in this post?
> Grossly erroneous? 2 arc seconds? A discrepancy of 0.16' in 8,751.24'?
The numbers are in fact a real comparison of the grid bearings reported by the original survey as derived from solar observations to those from a resurvey by GPS. The complaint about the "obvious error" is of course comic. The distance error of 0.16 ft. on the last line was in effect over 29,400 ft. (the total length of the actual surveyed connections between the two endpoints) and didn't keep me awake at night.
The longer lines were well clear of the ground and the angles along them were measured when scintillation was negligible, which is part of the reason why the results were relatively good. The real point of this example, was just to show how close to grid bearings you can get with solar observations. These results are fairly typical of what I see when I return to old work with GPS.
I can work with the error
Kent,
As long as you add 16 degrees to your bearings so's I can figgure the line w/ my compass, I can correct for your 2" bearing. If not, I'll just fishhook the blaze line at the end. (Or was that subtract 16 degrees?)
Personally, I'd rather be close but correct than precise and wrong, so I'll spend my time following in the footsteps of the original surveyor. You know, looking for stone walls, ancient fence, old foundations and stone piles that would be missed by occupying the "corners" and punching a button, or blindly following a bearing of questionable repute.
Now Kent, I know you've never made a mistake on a plat and all your sun shots are dead center but the rest of us mortals sometimes make an error. I still stand by the concept of actually locating the monuments and traversing around the parcel.
I will change my ways as soon as the boss tells me to and never look back, but I see magnetic bearing ruling in my area for the rest of my surveying days.
(for the record. If you have to ask yourself if the post is sarcastic, then it is.)
I can work with the error
> Personally, I'd rather be close but correct than precise and wrong, so I'll spend my time following in the footsteps of the original surveyor. You know, looking for stone walls, ancient fence, old foundations and stone piles that would be missed by occupying the "corners" and punching a button, or blindly following a bearing of questionable repute.
Ah, but the 1992 survey was an original survey. Those brass tablets in concrete were the original corners. So, if you'd dialed in your compass instead of actually running grid bearings, you'd probably be looking in the next county. The recurring suggestion that one can either be retracing an earlier survey or making accurate measurements, but not both, is comical, but not grounded in reality. The object of the profession is to do both.
Well, maybe so, but you didn't get paid to take a leisurely stroll around the countryside looking for those old monuments for a couple days. Nor did you get to pay someone to do it for you. That hurts the economy and people like me who like to get paid to solve the mystery, search for monuments, witnesses, accessories with compass and pacing, find monuments that others have not been able to because of the amount of measurement error at the time. I'm upset at the imminent demise of this part of the job just as much as Perry. But I can't come up with an argument against progress. My few jobs each year are still on compass or old deed bearing. But I may have to review solar procedures after this series of threads. Some argued we shouldn't teach it to students in this era of GPS, but we (Al Chace actually, not I) still do and I think the graduates are better for it.
> But I can't come up with an argument against progress..
We can underbid you by $30-$60.;-)
You ran a 3 mile with no intermediate monuments????
You ran a 3 mile with no intermediate monuments????
Now I'm finally understanding how surveying is done in Texas.
> Well, maybe so, but you didn't get paid to take a leisurely stroll around the countryside looking for those old monuments for a couple days. Nor did you get to pay someone to do it for you.
Actually, part of that project did involve locating some old boundaries, but the lines described run along the boundary of a piece that was severed from one side of a couple of larger tracts and I didn't think that newly established boundaries were supposed to be a challenge to future surveyors. There is no evidence that I've seen that we are about to run out of puzzles to occupy a land surveyor anytime soon.
You ran a 3 mile with no intermediate monuments????
> You ran a 3 mile with no intermediate monuments????
Actually, while 8,752 ft. may seem like three miles in New Hampshire, in Texas it would be about half that. :>
> Now I'm finally understanding how surveying is done in Texas.
No particular mystery. The survey represented above established the boundary of the newly created tract so that the adjacent landowners could have a problem fixed. There was a time constraint to get the conveyance of record, so actually running the lines between the concrete monuments happened a month or two later as a separate expense. Line stakes for fence construction were set, and an 8 ft. high fence was built.