so if I set 2 points with my gps rover and then occupy one with my total station while back siting the 2nd point and I have a distance variation of .10 does it make sense to reshoot the backsite point with my total station to give the accurate distance between the two points and then proceed with that tie-in?
It depends..........
Are you using your GPS in a ground system or a grid system?
Are you putting in the correct pressure and temperature for your total station?
Are you using the correct prism offset?
Have you checked the plumb on your rod(s) lately?
Have you checked and adjusted your tribrachs?
Have you baselined your total station?
The list goes on and on and on?ÿand on?ÿand on?ÿand on......
That would be within tolerance for RTK.
We leave 4-5 GPS points and then use 'freestation' when locking in with the total station
@jakehart yes that makes sense for the work that I do. ?ÿI like to choose the best two points?? total station agreement out of at least three GPS grid points on relatively small sites.
Quite likely that 0.1' is mostly in the scaling error between the state plane grid system your GPS points are expressed in, and the local ground system your total station measurement is in.?ÿ
Nevertheless, once you have your grid system scaling accounted for,?ÿ that total station measurement is going to be the more precise way to measure the relative distance between the 2 points.?ÿ GPS is the more accurate way to bring in geodetic positions relative to CORS stations remote from your site.?ÿ
Both of your GPS's points have some error (note that "error" in this context is not the same as "blunder", it is more akin to "imperfection") If you set up your TS on one GPS'd point, backsight the other, and retie the backsight point using the TS distance, you are holding the coordinate of the GPS you are set up on fixed, and hold the GPS bearing between the two. In other words you are saying that one point is perfect and the other has all the error of the two. That may be good enough for the task you have at hand, but it isn't the very best way to go about it.?ÿ ?ÿ ?ÿ
I would be very disappointed to see .1' between a GPS set of coordinates and a total station distance. First thing is to have a projection that is used for each one. I will use a DC for both shots which will keep my surface distance the same. If there is .10' something is wrong. So no, GPS control should fit better than that; RTK or Static.?ÿ
It depends..........
Are you using your GPS in a ground system or a grid system?
Are you putting in the correct pressure and temperature for your total station?
Are you using the correct prism offset?
Have you checked the plumb on your rod(s) lately?
Have you checked and adjusted your tribrachs?
Have you baselined your total station?
The list goes on and on and on?ÿand on?ÿand on?ÿand on......
This is, was, and shall forever be the only answer to a question of this nature.
so if I set 2 points with my gps rover and then occupy one with my total station while back siting the 2nd point and I have a distance variation of .10 does it make sense to reshoot the backsite point with my total station to give the accurate distance between the two points and then proceed with that tie-in?
I didn't catch this on the first reading...
Regardless of whether you change the distance between those two points, it will have no impact whatsoever on any points observed from that station setup.
I would be very disappointed to see .1' between a GPS set of coordinates and a total station distance.
A user recently posted (in a now deleted thread) about how pleased he was to see 0.14' repeatability in positions.?ÿ ?ÿ
We had good results so far on our current project with total station distances vs. GPS -derived distances. Points 1 to 2 and 2 to 3 were both within a few hundredths N - S and one hundredth E - W. I shot each point twice (on different days), 5 minutes each session. My PDOP was 2.1 or less, H residual 0.003' and V residual 0.007'. Had 14 satellites.
Pt 1 to 2
912.86' (C)
912.92' (C) geodetic distance
Pt 2 to 3
1418.52' (C)
1418.61' (C) geodetic distance?ÿ
Projection: SPC FL East
Use grid to ground ?? No
Geoid Model: g2003u07
I routinely set control points (in relatively clear places) with my Leica 1200, then later occupy those control points with a total station. The typical difference is 0.01 feet, and if I ever saw more than 0.025 feet I would start over. I've also taken the 1200 to a measured baseline and consistently saw the same 0.01 feet. All shots taken five times, one after another and averaged, using a bipod.?ÿ
A horizontal difference of 0.10 feet means something is wrong with either the equipment or the procedure, or both.
If I used NRTK to set control points, I would hold a "midpoint" between the two network pairs in order to better isolate each ones corresponding error.?ÿ Both Network Pairs have error (way more error than your total station, but I am neither going to ague for that nor say NRTK does not make good control). I would leave you receiver on the backsights while you are working and post postprocess when back at the office.?ÿ
so if I set 2 points with my gps rover
Come on, Mr. Jakehart,
As Hi-Staker said, "it depends". You have to be a little more forthcoming with your data. Your statement leaves out a lot of information.?ÿ
I know nothing about you and how you go about doing what you do, so no disrespect is intended or implied. I do not know anything about the project that you reference nor what specifications the project demands. Maybe a tenth of a foot is more than good enough. I don't know. There is a guy on U-tube doing traverses with sticks in the ground, fer krissakes.
I know the limits of my equipment and my processes and do exactly what you describe on many of the projects I do. I don't have the time, expertise and budget on any of my projects to seek one hundredth of a foot results with my RTK systems. Except maybe that "GPS on BM" point that I did a year or so ago. I expect better than a tenth of a foot, however.
I don't post-process any of my data. I will send data to OPUS and DPOS if I need ties to a particular coordinate system.
So, if are you just looking for some spirited banter on the subject, job well done. Lots of great ideas out there, as usual.
I love this place.
JA, PLS, SoCal
If I convert that to millimetres that we use here that is 3mm which is static gnss level accuracy in my experience, very difficult to even get a pole adjusted to that precision (pole run out etc.) especially if you change the height/rotate pole between shots to have independence between shots.
?ÿ
You stated five repeat shot averaged but how long were the shots and was there any significant time spread between them.
?ÿ
I'm also using Lecia 1200 base/rover which is GPS/GLO. Base on legs, rover on pole with bipod and using 30 epoch obs at 1 hz, <1km baselines. Only expect to get around 10mm hz 25mm v repeatiblity at 95% CI with multiple 20min+ time separated shots with perfect open sky conditions. Usually have 10-15 sats in solution.
?ÿ
Find it hard to believe results can be that much more accurate in other places in world?? I get the same amazing results sometimes also but not everytime such that I'd expect it. We are closer to the bottom of the world but still have good satellite numbers and geometry
Are you using your GPS in a ground system or a grid system?
Is geodetic distance synonymous with grid distance?
Have you baselined your total station?
Baselined as in checked on a calibration range? In 1994 we used a Topcon GTS-4A for an FDOT project, and we had to check the instrument on a calibration range before starting the project. We removed a side panel on the instrument and set a series of DIP switches to their proper positions.
?ÿ
Mr field hound,
Your questions lead to many other questions.?ÿ
N