California Surveyors Forums

For those interested in geodetic infrastructure...

Also posted at: http://csrc.ucsd.edu/

Good Stuff Greg,

Let's hope the author, Dan Roman, is back from military leave and working on improving the GEOID09 Beta model. Marti Ikehara identified hundreds of GPS height mod benchmarks in California that were left out of the Beta version.

This stuff is way above my pay grade, but below is a quote from a respected colleague in response to a question I posed recently about GRAV-D as it relates to floodplain mapping:

"[W]hat he has in mind is the use of ellipsoid heights in conjunction with a gravimetric geoid model to determine orthometric heights, without any use whatever of monumented bench marks. This is not going to happen within any reasonable time frame. As we have seen in Northern California, it's really not possible to assign accurate fixed ellipsoid heights to any mark. Even if a gravimetric geoid model were perfect, this source of error would undermine [his] proposal. But the gravimetric geoid model won't be that good, either. It will miss short wave length undulations, and will have to be corrected. The most precise and accurate way to determine delta geoid heights is by simultaneous GPS and leveling."

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