In a prior thread dealing with RTN/VRS observations, I described a project in which I took multiple 5-minute observations with a network rover on 10 NGS height modernization stations. What I didn't mention is an unexpected result when I brought the data into TBC, and I'm wondering if anyone has thoughts on what caused it.
When I loaded the job file into TBC, I got a popup asking me to select a geoid model, because the model referenced in the job file (GEOID03) isn't available in my TBC install. (I never bothered loading GEOID03, because by the time I switched to TBC GEOID09 was already available.) I chose GEOID09, and the vectors came in without complaint. However, the resulting NAVD88 heights differed from those shown in the field (TSC3) point list by 7 cm to 10 cm. The field values were closer to published, generally within 3 cm (though in one case off by about 7 cm).
Since the elevation results are consistent within themselves and within my error budget, I'm not concerned about the effect of this phenomenon on my project. However, I'd like to figure out why the differences showed up in the first place, and I welcome any insights you folks would like to share.
It turns out that I made a bad assumption: that there wasn't a lot of difference between GEOID03 and GEOID09 in my area of interest. I just ran geoid calcs using the NGS online tools for both models at one of my control stations, and the geoid separations are indeed 7 cm different between the two. So it's strictly a modeling difference, and has nothing to do with the field-reported versus calculated-from-vector-data results I was seeing.
I feel better now. 🙂