DPOS and OPUS Comparisons

J

James Suttles

Active Member
Attached is a PDF showing 7 days of static sessions that have been acquired and processed by DPOS and OPUS. They are 24 hour sessions with a 30 second epoch intervals. Since OPUS is GPS only and DPOS is using all available data, we do end up with some variables that are different.

I am pleased with the results and I have checked some physical monuments that were listed as 1st order, and the results are within 0.03' horizontally and 0.05 vertically.

Is this about what should be expected between the 2 different systems and multiple constellations vs GPS Only.

Either way, the results are stellar for my purposes.

Curious if anyone else has data that mirrors these results.
 

Attachments

  • Tower Position7-8 2021.pdf
    23 KB · Views: 199
Matthew D. Sibole

Matthew D. Sibole

Well-Known Member
5PLS
I would want @Alexey Razumovsky to take a look at your files. The one thing that stands out are the elevations on the 29th seem to be very high compared to the average as well as very high compared to the OPUS position. The overall RMS levels seemed to be better on DPOS than OPUS but the variation of elevations over the several days seem to fluctuate more with DPOS. Just my initial thoughts after a quick review.
 
Adam

Adam

Well-Known Member
5PLS
I'm curious how those check with the sessions you ran when you first got it? You should keep processing multiple sessions each month thru out the year and then average them. Maybe overkill to do it for a year but why not? Appreciate your feedback too. The Delta 3S is a work horse aint it? I used your base at 13 miles in the woods over in George Hildebran area a couple weeks ago. It saved me a trip back to the base to either move it or switch to tcp. Thanks Doug.
 
J

James Suttles

Active Member
Matthew D. Sibole said:
I would want @Alexey Razumovsky to take a look at your files. The one thing that stands out are the elevations on the 29th seem to be very high compared to the average as well as very high compared to the OPUS position. The overall RMS levels seemed to be better on DPOS than OPUS but the variation of elevations over the several days seem to fluctuate more with DPOS. Just my initial thoughts after a quick review.
Click to expand...
Mathew,

I re-ran the DPOS from the 29th, this morning and the results changed slightly in the horizontal, less than 0.01', but as you indicated the vertical is more in line with the other reductions. It changed from 1113.294 to 1113.149, so not sure what happened there, but its been over a week since the first reduction. Could it be that when it was reduced the first time, that all the data was not available at the time of reduction?
 
Adam

Adam

Well-Known Member
5PLS
James Suttles said:
Mathew,

I re-ran the DPOS from the 29th, this morning and the results changed slightly in the horizontal, less than 0.01', but as you indicated the vertical is more in line with the other reductions. It changed from 1113.294 to 1113.149, so not sure what happened there, but its been over a week since the first reduction. Could it be that when it was reduced the first time, that all the data was not available at the time of reduction?
Click to expand...
Check the DPOS reports and see if it was using the same CORS as the others
 
J

James Suttles

Active Member
That has to be it. First reduction only had 4 CORS and the one performed this AM had 5 CORS in its reduction.

So with that being said, what is a timeframe that needs to elapse in order to be sure we are getting the best configuration of CORS and a reduction that is not subject to change? I know that maybe a tough one to answer, but is there a rule of thumb, like 24 hours, 48 hours etc.
 
Adam

Adam

Well-Known Member
5PLS
I don't think there is a hard and fast rule on it. You get the Surveyors answer. It depends. I think what you are doing is good though. I would keep sending them until you get 5 CORS stations that are close.
 
J

James Suttles

Active Member
The receiver is close to north, probably within 30 degrees, its mounted on a tower, so adjusting it now will be a bit of a chore. The HI is 0.00, so not sure if that makes a difference.

If north is an issue, should those height differences not be evident in the OPUS solutions as well?

I have revised the spreadsheet to show the differences, looks like OPUS is about 1/2 of the difference in the height. Also noticed its about 1/2 the difference in Northing as well.
 

Attachments

  • Tower Position7-8 2021 revised.pdf
    29.3 KB · Views: 178
J

James Suttles

Active Member
Matt,

I reran 28,30 and 31. The only one that changed was 30, it changed 0.013' in the N and 0.003' E and Elevation changed a whopping +0.16' making it 1113.265. So not sure what the deal is there, its strange the variance in DPOS verticals vs OPUS verticals, could the other constellations be making the vertical differences. The RMS got better on 30, after waiting 6 days to run the processing.
 
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Jim Frame

Jim Frame

Well-Known Member
Was the receiver aligned to north? I noticed a lot of fluctuation in the heights from DPOS.
Click to expand...

I'm dubious about the concern for azimuth-dependent errors, especially in an RTK context. Most modern antennas have pretty tight designs, and unless you're including signals below a 10° mask (zenith angle = 80°) you're not likely to see much effect from misalignment. For example, a quick scan through the ANTEX values for the JAVTRIUMP_2A shows that the azimuth variations are sub-millimeter for L1 and no more than a couple mm for L2. (If you dip below a 10° mask you can pick up as much as a centimeter, but with RTK this may not matter anyway.)

Does DPOS impose a mask in its processing algorithm?
 
Matt Johnson

Matt Johnson

Well-Known Member
5PLS
To achieve the best results, the base and rover antennas need to be aligned to north. I did a test to prove this. The same settings with the Precise Topo profile was used. Two LS's were tested side by side in an open environment, one was aligned to north and the other was rotated 45 degrees. The base was aligned to north. Here are the results.

RTK Solutions with LS Rotated 45
1.png



RTK Solutions with LS Aligned to North
2.png



DPOS Solutions with LS Rotated 45
3.png



DPOS Solutions with LS Aligned to North
4.png


The averaged heights of the 4 different solutions all had good accuracy and were all within 0.01 feet of the known height. There was 0.05 feet horizontal difference between the averaged DPOS and averaged RTK solutions of the rotated LS. Rotating the receiver off north appears to have a significant effect on the accuracy solutions and some effect on the precision. The DPOS average and RTK average with the LS aligned north agreed within 0.005 feet horizontally.
 
Jim Frame

Jim Frame

Well-Known Member
I don't argue that antenna orientation is a best practice, but I remain skeptical of the magnitude of impact. The test Matt did is impressive in its duration -- I admire anyone who takes the time to run tests like this -- but I wonder how much of the very modest (statistically insignificant?) differences noted were due to individual receiver variations and physical positioning.

Maybe I'm misinterpreting the data presented, but it doesn't look like both receivers were tested in the 45° rotated position nor swapped between the two observed points to account for receiver and environmental anomalies. Without those controls it's hard to see the results as conclusive in light of the published calibration data.
 
Eric Tweet

Eric Tweet

Active Member
It's a shame that this day and age we don't have a PCO/PCV compensation algorithm chomping away at received signals in the background. Antenna calibration + magnetic direction readings ... *computing* ... snip out those pesky offsets ... Now all orientations are "as good as North"!
 
Adam

Adam

Well-Known Member
5PLS
etweet said:
It's a shame that this day and age we don't have a PCO/PCV compensation algorithm chomping away at received signals in the background. Antenna calibration + magnetic direction readings ... *computing* ... snip out those pesky offsets ... Now all orientations are "as good as North"!
Click to expand...

etweet said:
It's a shame that this day and age we don't have a PCO/PCV compensation algorithm chomping away at received signals in the background. Antenna calibration + magnetic direction readings ... *computing* ... snip out those pesky offsets ... Now all orientations are "as good as North"!
Click to expand...
Adjusting for orientation using the compass has been talked about in the past. Matt J, I think is the one who brought up the idea. Orienting the rover to North is not practical in many situations.
 
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