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Post Processing Variance: TBC 4.1 v Topcon Tools 8

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GNSS & Geodesy

Last Post by lee-d 8 years ago

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Dan Henry

(@dan-henry)

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Hi All,

Our firm has recently started trying to switch to TBC to post process static GNSS.?ÿ ?ÿFor years we've used Topcon Tools and had good success, but we didn't move on to Magnet

To make sure we've worked the kinks out, I've processed a few jobs with TT and then done the same adjustment in TBC.?ÿ In short, they don't agree.?ÿ The horizontals are reasonably close, usually less than 1cm but I'm getting significant elevation differences even after checking every conceivable setting.?ÿ ?ÿTo try and break the tie and limit the comparison to just the baseline processor and not our recievers, I brought in 3 NC CORS stations, 1 hour's worth of simultaneous data, and held one and post-processed the other 2.?ÿ In TT, I got horizontals within 1 cm and heights within 1-2cm of published values.?ÿ In TBC, the horizontals were similar and acceptable, but the heights were signficantly different, one over 5cm different from published.?ÿ I checked the velocity values for the CORS and the largest expected height difference from 2010 epoch?ÿ to 2018.75 is right at 1cm.?ÿ Any ideas what I can check to restore confidence in the TBC processing? As of now, we don't trust it.

Thanks in advance.

?ÿ

Dan

Posted : October 5, 2018 10:07 am

jhframe

(@jim-frame)

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Are you certain that the same antenna models are being used in both applications??ÿ Have you looked at the model parameters in each to be sure they're the same?

It's also possible that one application is using the full model parameters while the other is only using the phase center offset.

Posted : October 5, 2018 12:05 pm

Dan Henry

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TT doesn't seem to have a way to choose which antenna model to use, but looking in the antennas.xml for TT and the NGS Absolute values are listed.?ÿ In TBC, I had chosen NGS Absolute.?ÿ ?ÿI tried changing TBC to use the NGS Relative to see if that matched the TT solution better, but it made only a tiny difference in reported?ÿ heights.?ÿ?ÿ

Posted : October 5, 2018 12:19 pm

jhframe

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TT doesn't seem to have a way to choose which antenna model to use

The the processing report disclose the model it uses?

Posted : October 5, 2018 12:36 pm

Artie Kay

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Hi Dan

Have you asked whoever sold you TBC?

Wild guess - could it be down to selecting slant or vertical for heights and these being measured from different points on the antennas?

Have you checked the tropospheric model(s) that are being used? There can be substantial differences in height results between the different models in TT. Maybe TBC defaults to a different model to what you normally use in TT.

Posted : October 8, 2018 7:27 am

Dan Henry

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Jim,

Topcon Tools doesn't say which antenna model is used in the report or in the documentation that I can find.?ÿ ?ÿIt does use the NGS absolute values in the antennas.xml file that it draws from though.?ÿ ?ÿTBC does report the antenna model used, which is the same as whatever has been selected. Changing from absolute to relative in TBC seems to make only a couple hundredths of difference, which is a good deal less than the mismatch amount.?ÿ ?ÿ

Artie,?ÿ I did look at the tropospheric model and Trimble claims to have changed their modelling and baseline processing in the past couple of versions according to a white paper I just ran across.?ÿ I'm going to go straight to the dealer and see what they say.

Thanks.

Dan

?ÿ

Posted : October 8, 2018 8:00 am

lee-d

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What CORS stations are you processing against each other? I'm running 4.10, I'd like to test. There are CORS stations here that I get as much as 5 - 6 cm differences in the heights, but that's because they really do disagree by that much; I've been getting the same differences consistently for years.

Posted : October 8, 2018 9:20 am