[gdal-dev] Which Proj.4 transforms are available in GDAL?

[Even Rouault]

> The problem is that there is no EPSG code for the projection,

Ah, the -s_srs syntax is not limited to EPSG:XXXX. You can use a proj.4 string, inlined WKT, a 
filename that has WKT or proj.4 string in it, etc.
See http://gdal.org/gdal_utilities.html

> and NAD27
> datum is handled badly outside the US and Canada. The country in
> question is El Salvador, where they adopted NAD27, but it's not part of
> the NAD27 datum shift files. EPSG suggests a Ocotepeque datum, which is
> shifted to NAD27.


Isn'it the datum used by ?

$ gdalsrsinfo EPSG:5451

PROJ.4 : +proj=longlat +ellps=clrk66 +towgs84=205,96,-98,0,0,0,0 +no_defs 

OGC WKT :
GEOGCS["Ocotepeque 1935",
    DATUM["Ocotepeque_1935",
        SPHEROID["Clarke 1866",6378206.4,294.9786982138982,
            AUTHORITY["EPSG","7008"]],
        TOWGS84[205,96,-98,0,0,0,0],
        AUTHORITY["EPSG","1070"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","5451"]]

The TOWGS84 parameters are the ones of transformation http://epsg.io/6891 that is valid 
for El Savador (and neighbouring countries). There are other transformations from 
Octopeque 35 to WGS 84, but none have an area of use that include El Savador.
They are also transformations from Octopeque 35 to NAD 27.

Even

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