I want to convert TIGER data


to WGS84. How does ogr2ogr determine which transformation to use and how big would the introduced error be?

Study area is the county of Kauai in Hawaii, USA.


Actually, ogr2ogr does not decide, it is up to the user to choose a suitable proj string. For NAD1983, the datum shift to WGS84 is 0, that is both use the same ellipsoid in the same position. Proj string would be:

+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs

or s_srs EPSG:4269 t_srs EPSG:4326

Your data is in degrees, so no transformation is needed.

  • 1
    NAD 83 = WGS84 for the original realizations only. That's no longer true. The TIGER data's (in)accuracy may mean that treating them as equivalent is a valid solution. For more accurate data, or that's on later realizations/re-adjustments, you may need to look for a NAD83 Pacific Plate / ITRF (WGS84) transformation. Try ngs.noaa.gov/CORS/coords.shtml for more information. – mkennedy Feb 12 '13 at 18:32
  • OK, but as far as I know ogr2ogr does not take care of any time frames yet. This presentation gives some hints for NAD83 in Hawaii: higicc.camp8.org/Resources/Documents/… – AndreJ Feb 13 '13 at 11:10

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