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

Question

I want to convert TIGER data

GEOGCS["GCS_North_American_1983",
    DATUM["North_American_Datum_1983",
        SPHEROID["GRS_1980",6378137,298.257222101]],
    PRIMEM["Greenwich",0],
    UNIT["Degree",0.017453292519943295]]

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.

Answer 1

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.