More Surveying in Rural Texas

Just as a footnote on the subject of the uncertainties of OPUS-derived positions, here are the details of that one. Everything was tied from one control point with horizon-to-horizon sky view.

A receiver ran on that control point for two days for more than eight hours each day and I got an OPUS solution for each day's observations, each of which used nearly completely different CORS sites for reference stations:

In terms of the size of the residuals, that's about 0.02 ft. from each day's solution to the least squares estimate from both solutions. The CORS sites were at an average distance of about 130km from Control Point No. 1.

The two rock mounds shown in the photos above (or, more exactly, 60d nails that I found in the mounds) were Pts. Nos. 52 and 52. How accurately positioned were they? I'm going to say "pretty well":

[pre]
Error Propagation
=================

Station Coordinate Standard Deviations (FeetUS)

Station N E Elev
1 0.012 0.010 0.014
52 0.016 0.015 0.017
53 0.017 0.015 0.017
[/pre]

52 AND 52

Now you have me confused. It can't possibly be a mistake.

52 AND 52

> Now you have me confused.

52 and 53. The takeaway from the above is that they are essentially exact positions obtained using different CORS sites on different days that agreed nonetheless quite well and the uncertainty in the OPUS-derived coordinates was propagated through the survey to get estimates of the uncertainties of everything else positioned by the survey smack dab in the middle of nowhere.

Excellent

Locked up tighter than a couple dogs in love.

Actually, fairly standard

Actually, those sort of results are so standard that it's easy to take them for granted. That survey is sort of interesting because obviously it took one helluva a lot more work to have run the connections that the 1953 surveyor did with transit and tape than it does to follow them with GPS, but there are still some retracement tasks that require cracking out a theodolite or total station.

Another interesting feature of the 1953 surveyor's work is that he ran a connecting traverse along a road and tied to USC&GS benchmarks along it. Why did he do that? Well, benchmarks were plotted on quad sheets. So, since he'd tied to two of them, a person could plot his work on the quad sheet. The triangulation stations in that area were typically much harder to get to than the benchmarks which usually had been placed along motorable roads of some sort.

Could we get a little more detail on the observations at 52 & 53, just get a sense how you are using OPUS on these secondary points?

You discussion is showing me I have some gaps in house software, access to advanced OPUS 'Project' (requires NOAA training session), to work out. Still the assumptions I have made using OPUS relative to positional error are being validated by your findings.

Much appreciated

> Could we get a little more detail on the observations at 52 & 53, just get a sense how you are using OPUS on these secondary points?

The connection to NAD83 via OPUS was made at Pt. No. 1. That L1/L2 receiver ran all day while I occupied a number of marks with an L1 receiver, the Trimble 4600LS seen occupying the benchmark in the photo below. Those observations were used in post-processed baseline solutions from Pt. No. 1.

When the whole network was adjusted in Star*Net Pro, the uncertainties in the position of Pt. No. 1 estimated from the covariance matrices reported by OPUS for each of the solutions 1Day52 and 1Day53 (scaled by a factor of 3.0), were propagated through the the vectors radiating from it (and their own uncertainties) to get the NAD83 uncertainties of all of the points positioned by the survey.

Not seeing antenna on the secondary observations I was unsure how they were being collected and processed. I like the mix and match you have put together and integration into the job flow. GPS on a beer budget thanks.

> I like the mix and match you have put together and integration into the job flow.

Yes, while the L1 receiver takes a longer session to get a good quality fixed-integer solution, the way that field work progresses it often really isn't that much of a net increase in time. In the case of the two rock mounds, the receiver was set up on one of them and run for 20 minutes to get a static baseline and initialize it for PPK. While that was going on, I was at the other rock mound taking angles with the total station to the peaks, using the pole with the GPS receiver on the other mound as a backsight.

Then, after finishing with taking the bearings from one mound, I shifted the GPS receiver to it and repeated the process with the total station at the other.

The mile and a half hike to the mounds took enough time that a few extra minutes to get solid positions on them was worth it.

That is some fine looking GPS country.

Great post as usual, Kent. Thanks for sharing with us.

So you are looking for something on the order of 1-5 minutes difference in the bearings (or angles) from the wrong rock pile? (depending on distance to the peaks)

What was the angle on the incorrect mound versus record?

> So you are looking for something on the order of 1-5 minutes difference in the bearings (or angles) from the wrong rock pile? (depending on distance to the peaks)

Well, the 1953 surveyor had actually taken bearings from both mounds (or more exactly the station marks in both mounds). Here is the comparison of actual to record on each:

[pre]
From Rock Mound No. 52:
Description Grid. Az. Rec. Az. Grid - Rec.
East Peak of 3 Peaks 232°07’12” 229°55’ 2°12’12”
Mountain Peak 110°52’00” 108°39’ 2°13’00”
Notch on Mountain Peak 72°09’11” 69°57’ 2°12’11”

From Rock Mound No. 53:
Description Grid. Az. Rec. Az. Grid - Rec.
East Peak of 3 Peaks 232°08’52” 229°57’ 2°11’52”
Mountain Peak 111°08’44” 108°57’ 2°11’44”
Notch on Mountain Peak 72°16’00” 70°04’ 2°12’00”
[/pre]

Great post,

thanks for the insight in the Texas surveying,

Chr.

Very interesting. I kept looking at that THING on the ground behind the Trimble GPS receiver in the second photo from the top. What in the world is that? Your scarf? I thought it was hot down there! Or, is it perhaps a THNEED?

> I kept looking at that THING on the ground behind the Trimble GPS receiver in the second photo from the top. What in the world is that?

That's an ancient yucca plant that had fallen over on top of the rock mound and was still growing. :>

I am in country like that weekly. My guess is that you are working in the Big Bend Country?

> My guess is that you are working in the Big Bend Country?

Yes, the basaltic rocks and the background of mountains in Mexico couldn't be anywhere else in Texas that I know of.