[Proj] Unknown Datum

Jean-Claude Repetto jrepetto at free.fr
Thu Nov 25 09:42:17 EST 2010

Le 25/11/2010 14:25, Kassiane Mentz a écrit :
> We are in a city in southern Brazil (Porto Alegre - Rio Grande do Sul),
> and have a lot of maps that have a
> unknown local Datum.
> We are using an application that uses Mapserver webmapping but is having
> trouble with our maps becouse
> they were using an unknown datum, even our forecast and our ellipsoid
> are known.
> Trying to makem with the mapserver automatically convert our maps to
> WGS84, which is what most
> approached our features, we decided to insert a new proj4 Datum.
> In file PJ_Datums.c we inserted a new reference vector in pj_datums []
> for our datum, passing the parameters
> conversion. Also insert an entry in the archive world for our specific
> case.
> Compiled the library with our modifications and uses MapServer to
> perform a test. Using the command Shp2img, we realized that this stopped
> working, which indicates that something happened in Proj4.
> We would like to know if there really is a way to include a unknown
> Datum to the proj4 perform the conversion.


You don't need to change the PROJ.4 source code. Just use the +towgs84 
parameter to perform the datum transformation.


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