Hello,
We recently had a Topcon Hiper+ get blown over by the wind. We sent it to our dealer to get fixed and have received it back. I am going to set the unit up over some known points as a check to make sure it is working okay. Is there anything else I should be doing to make sure the equipment is functioning properly? Is there a way to test the centering like on a total station? Any suggestions or ideas would be appreciated.
Others can chime in here, and do this a better job than I can.
I heard this story:
Back in the old days, some surveyors set GPS receivers out. They had a cluster of 3, as I recall.
They did LONG observations, and ran closed loops. What began to show up was a systematic error, or something less than a hundredth in magnitude. maybe 0.003 feet. Michael Brady, (Then in Hot Springs AR was involved)
They contacted Dr Javad, and asked what was up.
In his broken, Syrian English, he said: Thats as accurate as they can drill the holes in the mounts at this time, and we were not worried about that amount. It will go away in later models, when we do it properly, with jigs and machines.
This was in the early days, of GPS.
It showed up, when the GPS units were all oriented to north, at one side of the antenna. They had an arrow, you were supposed to point north.
I have also heard that there is a "Ghost" above the antenna, that functions as the actual antenna. This "Ghost" is like a magnetic little bump that sticks up, above the antenna, maybe a few inches. So, IF I wanted to "Test" an individual unit, I'd do it like this:
Set up 2 GPS units. On tripods, with sand bags on the legs, or weights. Make the setups VERY stable, so that motion of the tripod is mitigated. Orient them BOTH to north. Let them cook for 24 hrs, POST process the data, HOLDING the one you are NOT testing as a FIXED location. Then, the one you are questioning, Rotate it 180° to SOUTH. Cook again for another 24 hrs. Do this 3 times. Since you are ONLY rotating one of them, then that is the one that should change. You should find your error of unit doubled. IT should be repeatable. The 2 GPS units should be less than 100' apart, so that the ionospheric conditions are fully identical. Turn off the one that you rotate, so it forces a NEW file for the observation. Turn them on and off at close to the SAME time each day. This will give you a whole 24 hrs, per observation, and the observations will be a near complete cycle of the GPS constellation, + - maybe 6 minutes of time. This should give you a good idea of the answer to your above question.
And, of course, PUBLISH the results for us all to see, twiddle our thumbs, and consider!
🙂
Nate
Anybody else want to chime in, this is my thoughts.
Nate
Gosh Nate, that sounds like overkill to me! I would occupy known points, that is NGS benchmarks or shared solutions from OPUS. I would occupy the same points on different days, different times of day, twice. I don't think that you have to worry about orienting the antenna north unless you have an older model and it's required.
As for centering, that's a tribrach issue, check the tribrach.
Dtp
He wants to check the GPS unit. IF he does what I said, he will have isolated ALL the error, in that GPS unit. What I am saying, is I think it will accomplish his goal. IF he does what you say, then he also has to figure in all the other equipment... tribrach, Plummet, etc.
What I said, actually isolates the item he wants to check.
Tunnel Vision Nate
We always took all our stuff to a well-known local CBL with 4 published NGS marks. They were alongside a grass field runway at a usually unattended airport. Whenever someone was there we checked in to let them know who we were and what we were doing. Poor old guy seemed like he was happy to have the company and pretty much let us have the run of the place. All the times we were there, we never had any air traffic.
What did I expect on some lonely backwoods grass airfield in the remote mountains of western NC. 🙂
After you do this swap the antennas and observe for another 24 hours. The repaired receiver should have the same deltas on the point as the control has. This will eliminate the Tribrachs and other mechanic oe error sources.
I just did 11 days of observations on a point with an OPUS X90. The Range of the coordinates was 3mm in north and east processed tom
Opus on the 11 observations. I am waiting for the concrete to dry on a pillar. When I start observing on it, I will run 10 days on the pilar and swap receivers and see what happens. I will have one on a fixed height tripod about 2 kilometers away that we will running full time.
To test the verticle, set them side by side, on a level plate, attached to a tripod, or similar thing. They should render the same vert.
N