[gdal-dev] Re: EPSG value

[Even Rouault]

Selon Bill Teluk <Bill.Teluk at team.telstra.com>:

> If I understand correctly from above, would it be correct to say that if
> ogrinfo/ogr2ogr doesn't see an "EPSG" value specified in the WKT, it cannot
> derive the EPSG code? eg. the ogr utilities won't translate a WKT to an EPSG
> code?

Exactly. OGR will not try to guess the EPSG code if it's missing in the WKT. I
assume that the below WKT come from shapefiles ? ESRI WKT doesn't include EPSG
codes... And I'm afraid that even if we tried, it wouldn't be possible to guess
the EPSG code because the WKT definition could possibly come from other
authorities than EPSG, or due to the loss of info in ESRI WKT, you could also
perhaps find several EPSG SRS that translate the same...

>
> I ask because I have a dataset that is in GDA94, but uses an unusual WKT for
> the CRS spec (and there are no EPSG's specifed) - when we used ogr2ogr to
> load it into Postgis, it created it's own SRID (900914) instead of using
> 4283.

You can workaround this by adding -a_srs EPSG:4283.

>
> Below are two GDA94 WKT's, neither of which translated to the "expected"
> EPSG/SRID.
>
> Thanks in advance!
>
> Layer SRS WKT:
> GEOGCS["Unknown",
>     DATUM["GDA94",
>         SPHEROID["GRS_80",6378137,298.257222101]],
>     PRIMEM["Greenwich",0],
>     UNIT["Degree",0.017453292519943295]]
>
>
> Layer SRS WKT:
> GEOGCS["GCS_GDA_1994",
>     DATUM["Geocentric_Datum_of_Australia_1994",
>         SPHEROID["GRS_1980",6378137.0,298.257222101]],
>     PRIMEM["Greenwich",0.0],
>     UNIT["Degree",0.0174532925199433]]
>
>
> --
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