[OSRS-PROJ] Datums supported by Proj.4

[Frank Warmerdam]

Jesus Angel del Pozo wrote:
> Hello.
> 
> Thanks for your answers about the comparation between Geotrans and
> Proj.4. I like the identifiers and comments of Geotrans, but I'll just
> use the API so the source code is not very important to me. Nevertheless
> I think its better to have a clear source code.
> 
> Now I have another question about datums shifts. I have seen that Proj.4
> works with lots of proyections and ellipsoids, but there are only a
> few datums:
> 
> __datum_id__ __ellipse___ __definition/comments______________________________
>        WGS84 WGS84        towgs84=0,0,0                 
>       GGRS87 GRS80        towgs84=-199.87,74.79,246.62  
>                           Greek_Geodetic_Reference_System_1987
>        NAD83 GRS80        towgs84=0,0,0                 
>                           North_American_Datum_1983
>        NAD27 clrk66       nadgrids=conus,ntv1_can.dat   
>                           North_American_Datum_1927

Jesus,

I like to this of these more as examples than anything just now.  Since I
don't have an obvious naming system to apply, and because for many datums
folks have different wgs84 shift parameters they like to use depending on
their area of work and so forth, I have avoided populating a large list
of datums.  You can provide you own datum definition in a definition by
supplying the +towgs84= parameter yourself (and the ellipsoid def).

There are some examples of this in the epsg file, though for EPSG datums
with more than one available transformation to WGS84 I did not produce any.

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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