[Gdal-dev] OGR's importFromEPSG depends on libgeotiff?

[Ben Discoe]

> From: Frank Warmerdam
> Sent: Thursday, October 06, 2005 5:08 PM
> 
> > what method provides the inverse of importFromEPSG().  
> > That is, given a common CRS in an OGRSpatialReference, can 
> > it return an EPSG coordinate system code
> 
> Unfortunately this direction does not exist currently as a 
> method on the OGRSpatialReference.

Interesting, that is surprising.  I don't know the internals of GeoTIFF, but
i always assumed it used an EPSG code to store projection, so the GeoTIFF
code would need to have such a function somewhere.  I tried to study the
code to learn how it is done, but the GeoTIFF code is quite complex.

> In libgeotiff there is a function
> GTIFMapSysToPCS() that does that a bit for some simple cases.
> But it only works for a few common hardcoded cases (ie. UTM WGS84).

Indeed simple, and it doesn't work on a OGRSpatialReference. I found it in
geo_extra.c, and it doesn't appear to be called.

> It has been an ambition of mine to some day build such a thing.

I would be very curious to know what GeoTIFF _does_ store for CRS, if it's
not as simple as a single integer EPSG code.

Thanks,
Ben