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I have some data (points and rasters) that I would like to be able to convert to and from several vertical datums, including MLLW in coastal Florida. I would appreciate it if people could provide some insight into accuracy, pitfalls, requirements, etc. of using available utilities such as VDatum or corpscon. Is one more user-friendly than the other? Are there any others that I should consider? Thanks!

  • CORPSON 6 converts between NGVD29 and NAVD88, and supports 6 geoid models. It doesn't handle tidal datums like converting between MLLW and MSL, for instance. – mkennedy Jun 30 '11 at 21:30
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If you are doing vertical conversions over the ocean you really need to use VDatum.

Vdatum runs a detailed, unstructured mesh tidal model (ADCIRC model, usually), then computes tidal coefficients, generates an 18.6 year time series, then determines surfaces of MLW, MLLW, MHL, MHHW, etc. These surfaces are then evaluated at known tidal gauge locations, and the deviations are used to fit another surface which is then used to adjust the grids so there is no error at the gauge locations.

In the final step they intepolate to a regular grid, which forms the basis so the software conversion. But you can ask for the original surfaces on the original mesh (usually triangular) as well. I did this when I was correcting datums in the Gulf of Maine.

Good luck!

Rich

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You might also consider GDAL via OSGeo4W, which has the ability to do vertical datum transformations. I don't think that the OSGeo4W build has grid files for coastal Florida, but they could be developed. Search the GDAL Trac wiki or ask on the gdal-dev list for more information on how to develop your own .gtx grid file for coastal Florida.

GDAL, of course, has the advantage of being much easier to use than VERTCON, VDatum, or corpscon with the ability to open just about any vector or raster format.

  • Thanks for the suggestion. I keep seeing people talking about GDAL, which I've never used, so it's something that I'll have to look into. Can I access the vertical datum transformation functions through Python or do I have to install OSGeo4W? – Jason Jun 30 '11 at 19:19
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I loved Corpscon when I did a lot of datum conversion because it was stand alone and I'm not a programmer.

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