[OSRS-PROJ] Conversion between Geographic CS's

Frank Warmerdam warmerdam at pobox.com
Wed Oct 2 23:56:47 EDT 2002

Luis Mota wrote:
> Hi.
> First of all, I must say I have never used PROJ.4 before. I am posting 
> to this list because I am a user of PostGIS, which uses PROJ.4 to 
> perform transformations between Coordinate Systems (CS).
> In PostGis, there is a transform function that is supposed to transform 
> between any kind of CS. As far as I have understood, the conversion 
> between projected CS's works fine, but now I am trying to convert 
> between geodetic CS's and everything is going wrong...
> So, my questions to you would be:
> - is it possible to convert between geodetic CS's?
> - is this very different from converting between projected CS's?
> I am sorry to post such a simple question, but I don't seem to 
> understand much from the online documentation...
> Bye and thanks in advance


By geodetic, I gather you mean lat/long coordinate system normally in degrees
based on an ellipsoid and a datum?

These would normally be described in PROJ.4 with a "known" datum like:

  +proj=latlong +datum=WGS84

or with a user defined datum (3 or 7 parameter transform) based on an
ellipsoid defined something like:

  +proj=latlong +ellps=GRS80 +towgs84=2,5,-15

I hope this helps.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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