I recently ran a open traverse from one gps pair to another. We did shoot gps on a point in the middle to use as part of our traverse solution. Our traverse did not close very well as is generally the case when running from gps pairs to another set of gps pairs. How do i incorporate that middle point into the traverse solution and adjustment? I am only familiar with adjusting traverse from closed loop or open traverse, but not incorporating a mid point into the solution. I hope i am being clear and concise with my explanation. Thanks for all the help in advance guys!
Sounds like the first thing you need to do is apply combined scale factor corrections to your ground distances. See if that tightens things up some.
Are You GPS Occupations Independent Or A Network?
You have 5 GPS points, only one of which can be held, everything else requires latitude in the adjustment.
Only a network of GPS can be on the same level with a traverse, so explain what you did or did not do.
Paul in PA
send me your data; I will give it a look. add any details, if necessary. email is in profile
I don't understand your statement that Our traverse did not close very well as is generally the case when running from gps pairs to another set of gps pairs. If they do not close well consistently, you must ask yourself what you are doing wrong in the computations.
Here is how I used to compute traverses in the pre-GPS and pre-PC days...
1) starting with one station and BS, compute the traverse using raw horizontal distances (mean the forward and back)
2) using the preliminary coordinates and elevations in step 1, compute a scale and elevation factor for each point
3) recompute the traverse using mean combined scale factors for each segment (i.e. mean of the standpoint SF and the forepoint SF)
4) check closure at known points (i.e. the one in the middle and the pair at the other end)
5) adjust the traverse using one of several non least squares methods
and now, with PC's...
1) put all of the data into a least squares adjustment and perform a minimally constrained adjustment (i.e. hold one pair fixed)
2) check closure at known points
3) perform a constrained adjustment holding all of the control
If you are getting larger than expected misclosures in step 2, then you either have bad GPS or bad traverse data.
Hi-jack
John - did you get my email?
Hi-jack
I did, Dave...not sure what that is, I cannot get any of the smaller pictures to open. I think it is a set of targets or maybe heliotropes?
Hi-jack
I think they're targets, but more importantly it is the tribrach style you wanted a while back.
Our traverse did not close very well as is generally the case when running from gps pairs to another set of gps pairs.
The traverse should close between GPS pairs, it's good you can put one in the middle, but it should also have been almost "dead" on. If the closures aren't very good then I would not adjust to something like that. I'd find out if there is a blunder or a systematic error (which is probably the case-mismatched projections would be my guess).
Hi-jack
Yes, they look like that but I wonder what the diameter of the hole is. Looks bigger than the "zeiss" style.
:good:
The traverse was about 4400 feet long, not a good shape at all and 30 some stations long. Not ideal, but now we are just trying to make it work. Traverse was run with a leica robot and viva data collector. We have never gotten better than around 1 in 25000 unadjusted closure between gps pairs. Closed loops close great as expected. We got some support tonight to deal with some of the issues and that seemed to help. At least the vertical closed under 0.01.
Closed loops close great as expected. We got some support tonight to deal with some of the issues and that seemed to help. At least the vertical closed under 0.01.
1:25000 is good for short turn traverses, my experience with our trimble stuff is usually better than that. If you are closing on yourself then I would suspect there are issues with projections. Your ground traverse and GPS locations may not be working in sync, this was an issue many years ago with us.
Once we syncd up the two types of surveys (it meant an update to how the DC handled conventional shots), that went away and really there is often nothing to adjust out of many of our short traverses we do now. No real reason to adjust .01' out of a two point traverse, but of course 30 turns would be another issue. I would really dig into the raw data and be sure it is handled the same way with the conventional and GPS traverses, and I only so this to static points, that would also tighten it up compared to RTK or VRS. And be sure to adjust between the static points. Apples to Apples
