Base File reductions and which post processor to use?

James Suttles

Active Member
I have compiled base file reductions using DPOS and OPUS. I have broken them down into OPUS, JUSTIN and GIODIS.

I am confident the OPUS and GIODIS, use only GPS signals. JUSTIN I believe uses all available constellation data.

Is this the results that we should expect to see, and is one processor preferred over another. I know the OPUS solutions are not processed by DPOS, but its very interesting that the reduced coordinates are similar in one axis or the other, depending on the processor.

I feel that GIODIS with the 8 CORS stations in the reduction, is probably the most diverse solution. The elevation of GIODIS seems to be the lowest, with Justin elevations being the Highest and OPUS elevations being somewhat in the Middle.

So if setting control and using static files, which processor would yield the best real world coordinate, or are there too many variables to account for?

These are all 24 hour files collected at a 30 second epochs.
 

Attachments

  • Tower Position OPUS - JUSTIN - GIODIS 10 days.pdf
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Shawn Billings

Shawn Billings
5PLS
Great report, James. I did something similar several years ago with the Triumph-2.

Question: Were you concerned with the orientation of the receiver (also what sort of receiver was it)?
 

James Suttles

Active Member
It's a Delta S3,
North is something to consider, but was not accounted for in this set of solutions.

I have checked some first order marks using the base and LS plus and the difference was roughly 0.03' horizontal and 0.05' vertical. Granted they were geodetic traverse stations and not GPS derived stations.
 

Shawn Billings

Shawn Billings
5PLS
It's difficult to say which processor is best. It's interesting that the RMS reported by OPUS appears to be so pessimistic. I suspect that is because NGS can afford to set user expectations lower with the higher error estimates, since it's a free service and doesn't really have market competition. However with its higher error estimates the results are more consistent. This repeatability (i.e. precision) doesn't necessarily mean the solutions are more accurate, but it could. It's possible that there is some bias that would cause the results to be very consistent (precise) but to be off by some constant. The other thing to note is that the data being used isn't exactly the same, so the question is not only which processor is better, but also which procedure is better. The additional 3-5 CORS stations used by Justin and Giodis may be injecting additional error in the solution if the stations are not stable. The use of additional constellations may also provide additional error due to timing differences and other signal issues that are above my head.

So it may be that using only GPS or a combination of GPS and Galileo only is better than all constellations or that the three CORS are better than the eight.

Precision is definitely a very good place to start, but I believe once you are in the centimeter range deep questions start to emerge such as Pilate's famous question "What is truth?"
 

Shawn Billings

Shawn Billings
5PLS
It's a Delta S3,
North is something to consider, but was not accounted for in this set of solutions.

I have checked some first order marks using the base and LS plus and the difference was roughly 0.03' horizontal and 0.05' vertical. Granted they were geodetic traverse stations and not GPS derived stations.
You're going to find it difficult to find something more accurate than what you have from your various solutions (any one of them) that you'll be able to "truth" against.
 
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