IMO, your horizontal centering errors could be tightened to 0.001m, and your vertical centering loosened to maybe 0.004m. That simple thing?ÿ might be enough to normalize your statistics.
I have found that Measure ups are a real weak point. Get several guys to measure the same measure up independently and you are going to get a surprisingly large range of results. Half a centimeter, maybe more, is totally reasonable. One thing about doing a lot of LS adjustments is that it educates you about what your errors actually are.?ÿ ?ÿ ?ÿ ?ÿ ?ÿ
With regards to holding the GPS points fixed - as others have said in different ways - those coordinates are not perfect. I understand that, nevertheless, project management considerations may oblige you to hold them fixed. But that just means that their error must be distributed into the measurements. Doing so means that you may have to dial up the error settings of those measurements unnaturally to get statistics to "pass" chi-square.?ÿ My favorite way of dealing with that is to mess with the centering errors.
Also - the vertical component of a GPS determined coordinate is always the weakest. A couple of tenths of a foot in each point is very possible. Better can be done but it isn't guaranteed at all.
StarNet, generally, strokes my ego better. Wow that??s a great survey Dave! Wonderful statistics! You are obviously the greatest surveyor on earth! I go back 5 years later and don??t match myself that well, not bad but it points out how accurate I really am.
TBC will nag me about loose sets which is handy. Really easy to disable a bad set of angles. I take 4 sets, then look at the individual statistics, and if I have a loose set I tap Round+, that way I have an extra set to dump, I can dump 2 if need be and still have 3 left. This happens mainly on Forest traverses with steep loose ground.
I can make TBC happy but it??s more like your mother, okay if you think that??s good enough I guess it??ll be fine.
I use TBC exclusively at this point.
In the case at hand I would hold one point fixed and adjust my survey within itself, using only 1 point name per point. See how that matches the other given control coordinate values.
Personal thing. Tapes are ok, but when it lands in the middle of the .01, I just spin and win. The pointy tip also ensures the location is a precise one and not subject to which random person is flailing away on the BM or Cap or whatever.
There are methods that will tighten up the spread in measurements, but there are none than will eliminate it. The?ÿ tent pole is one. Leica has a measure down hook.?ÿ There is the 2 meter fixed height rod. All these will beat the box tape measure up hands down. But 2mm is at the very limits of achievability even for these methods.?ÿ Plus you have to consider just what the dumb end of the tent pole is founded on.?ÿ
For my GPSonBM sessions I measured 3 places around the ground plane, using the Trimble pole, at the start and at the end of he session, and was disappointed if all 6 measurements did not round to the same1 mm increment.
I did not try to compensate for the dimple in the disk, so was probably a half mm off.?ÿ NGS did compensate for the dimple on the GSVS runs.
For my GPSonBM sessions I measured 3 places around the ground plane, using the Trimble pole, at the start and at the end of he session, and was disappointed if all 6 measurements did not round to the same1 mm increment.
Consistently reading the scale is a good thing, but it doesn't translate as perfection. There are plenty of other sources of error in the system. Get the guy beside you to repeat your procedure and he will get a different number, and repeat it at 3 points around the perimeter.?ÿ And that doesn't make either of you wrong. We just have to accept that these errors are a part of our lives. Plus, the sort of care and attention you can give measure ups on a GPS on BM session is going to be much greater than what is reasonable to expect when traversing control.?ÿ ?ÿ
The original post from the other thread (Collecting-Processing static Data for DGPS) indicates you came into this project after it started.
Quick summary (paraphrasing), "a point at the start that they're holding, setting up a base on that point, running 3-4 hours of static using a rover on all their main control hubs. They're importing those T02 files into TBC, manually entering in point numbers and heights ect, processing baselines, then using TBC to adjust the coordinates to get them into a ground system."
If the original field method is as you say, the original static data collection set for the main control hubs should be golden. What they did after that, is a bit murky.
If this is a case of densifying the control network from a preexisting "ground system" (site calibration?), it may be a matter of making all your new measurements, correctly adjusting your dataset, and then fitting to a site calibration or something like that? It seems that the "working" control values already have some of these concepts already baked in, but we don't know what they are.
Not sure how they arrived at "ground", but it sounds like they may have started in some form of geodetic grid, and did who knows what after that?
In my experience, I have 2 guesses about how the vertical (and the horizontal?) may be, or became wonky in this case: 1. The original "adjustment" was performed, and they held 2 points (endpoints?) fixed vertically, which instantly gave you the slope across your project extents. 2. Somone applied an average combined scale factor for your site across the individual coordinate values in Excel, or similar.
Which is why, separately, the gnss is good, the traverse is good (hz & vt, but may indicate otherwise at the moment), and the levels are internally consistent, but nothing matches your "control".
Might be possibly mixing some random ground system (translation/rotation/scaling issues) with some new good intermediate control on some particular geodetic grid, which is why it's fubar.
I could be wrong about all that, but let's see what else you got?
The following questions might help us figure out where you came from, where your're at, and where you're going, becasue you came in during the middle and you're trying to make it match:
How many "main control hubs" are there already computed before you got there? What was the original coordinate system and method of adjustment those positions were derived from? How did those positions get transformed into a "ground system"? What are the parameters of the existing "ground system" you have to match?
Plus it's a far sight easier to measure to a round antenna with a fixed graduated rod where you can get a straight line from mark to edge of antenna (thinking the Trimble zephyer geodetic flying saucers)
?ÿ
Find with total station you end up " bending" the box tape around top of tripod head and then still can't get exactly to the dimple as battery/storage card knobs in the way (Leica/Geomax) so even if you use the onboard application that converts the slope distance measured to a vertical distance you have some systematic error.?ÿ I've taken to rounding down to nearest mm to try account for top of tripod making slope slightly longer than a direct measurement.
?ÿ
To do it properly would need to measure a slope distance from mark to top of tripod and convert to vertical distance plus measure from top of tripod to dimple on instrument but with that method even more chance for a mistake in measure up!! Wonder if Leica's auto height would fix that?
?ÿ
Only way to accurately transfer levels with total station for me is to only measure to marks with pole at fixed height and instrument not over marks; i.e traverse by resection of you also need positions
I've taken to rounding down to nearest mm to try account for top of tripod making slope slightly longer than a direct measurement.
Try doing the trig calculation on that and I think you will find you are under-compensating. Working in feet, I round down to the nearest hundredth of a foot, and then cut another hundredth.?ÿ That would equate to cutting 4 or 5 mm.?ÿ The mark on the instrument that I'm measuring to is about 2mm wide.?ÿ
Bottom line is that the vertical centering error I use in StarNet starts at 0.01' and I'll dial it up to double that without undue concern.?ÿ
Constrain to ONE POINT (you can have one H and one V). Set a Bearing to the another station.
After you have everything working from that, then you can warp it and constrain as you like. But MINIMAL constraints is critical to getting having the software tell you what you need to know. You can have great "results" by constraining willy nilly...
Of coarse there will be many more redundant measurements made, but I'd like to figure out what is going on first.
What do the station reports reveal? You can examine what is happening at each station, and that allows you to refine the issue that you are looking at. Sometime inconsistent measure ups are revealed in the reverse shots from station to backsight. Also, this can show if you are missing something or if your approach is creating some sort of issue in the data.
My suggestion to let all the coordinates float a tenth is my step before holding ONE POINT, to test the measurements vs. the given coordinates. If one of the given "control" points is off, no point in holding it fixed. Star*Net allows holding or giving a standard error to multiple connected points in place of specifying a fixed bearing.
Find with total station you end up " bending" the box tape around top of tripod head and then still can't get exactly to the dimple as battery/storage card knobs in the way (Leica/Geomax) so even if you use the onboard application that converts the slope distance measured to a vertical distance you have some systematic error.
That's the precise reason why Trimble instruments have the notch measurement method. No wrapping the tape around the instrument. Doesn't stop some of our crews from trying, though...
IMO, your horizontal centering errors could be tightened to 0.001m, and your vertical centering loosened to maybe 0.004m. That simple thing?ÿ might be enough to normalize your statistics.
I have found that Measure ups are a real weak point. Get several guys to measure the same measure up independently and you are going to get a surprisingly large range of results. Half a centimeter, maybe more, is totally reasonable. One thing about doing a lot of LS adjustments is that it educates you about what your errors actually are.?ÿ ?ÿ ?ÿ ?ÿ ?ÿ
With regards to holding the GPS points fixed - as others have said in different ways - those coordinates are not perfect. I understand that, nevertheless, project management considerations may oblige you to hold them fixed. But that just means that their error must be distributed into the measurements. Doing so means that you may have to dial up the error settings of those measurements unnaturally to get statistics to "pass" chi-square.?ÿ My favorite way of dealing with that is to mess with the centering errors.
Also - the vertical component of a GPS determined coordinate is always the weakest. A couple of tenths of a foot in each point is very possible. Better can be done but it isn't guaranteed at all.
Good point on the centering errors, I made that adjustment along with my vertical angles the chi values for zeniths is about spot on with the rest now.
