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What's your opinion?
Posted by Mapman on December 27, 2013 at 6:39 pmI’ve been doing more and more fast static using OPUS and I am slowly coming around to using it with confidence. But was wondering if there are any horror stories out there using it. Or if not, how accurate are you getting your results? Just curious.
Borderline Survey Pro replied 10 years, 8 months ago 4 Members · 4 Replies -
4 Replies
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If the job takes more than one day it is simple to collect OPUS for a second day, and compare results. Or collect separate sessions on the same day. That will give you the measure of how repeatable the results are.
I’ve had OPUS-RS match up to much longer duration OPUS within a few hundreths but it depends on how many CORS there are in your area, just where they are, and the multipath at your receiver.
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> I’ve been doing more and more fast static using OPUS and I am slowly coming around to using it with confidence. But was wondering if there are any horror stories out there using it. Or if not, how accurate are you getting your results? Just curious.
The “how accurate” to me means what scalar should be applied to the values reported in the variance-covariance matrix that OPUS reports for the estimated undercertainty of the solution. One way I get at that number is when a station is occupied for hours, to cut the RINEX file into separate occupations of whatever duration I customarily use and adjust them all in Star*Net, varying the scalar until the Chi Square test values are in nominally perfect agreement (variances of residuals are consistent with the scaled variances generated by OPUS).
I think you’ll find that the scalars typically fall in a fairly narrow and predictable range and so it isn’t unrealistic to apply the scalar determined by experience to the OPUS-generated uncertainties when multiple sessions aren’t possible.
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The repeatability is pretty consistent in our area. I shot 2 points in my back yard that I simply measured 15′ apart. Since I’m near sea-level, grid ratios aren’t much of an issue. I received my results back with an inverse distance of only 15.02′. Now with my receivers up there 2 meters I could easily have been off by .01′ on each setup.
The only issue I may have is the orbits don’t always get published soon enough. I would love to be able to get my results out in the field. But it always seems to take a few hours before rapid orbits are available.
Precise orbits results do not seem to be much different than the rapid orbits results. Maybe 2 or 3 mm’s at most. Also toyed around with using various CORS stations. Same general results. At least for me anyway.
Breaking the data down and doing it in Star Net never occurred to me. I’ll have to give that a crack. Thanks Kent.
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I use fast static, but I do have problems when I am in a calibrated grid, and use fast statick for whatever reason for a few points. I am not able to understand what the fast static is doing – I need to ask that question on this forum.
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