[Gdal-dev] use of .prj file

[Frank Warmerdam]

Doug_Newcomb at fws.gov wrote:
> Hi folks,
>       Using FWtools1.0.0b2  on windows  - gdal_translate with the -a_srs
> option with the following .prj file to define the projection in converting
> a tiff to an ecw file:
> 
> PROJCS["NAD_1983_UTM_Zone_18N",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-75.0],PARAMETER["Scale_Factor",0.9996],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]


Doug,

The problem is that the ECW writer has a bunch of rules on how to
recognise NAD83, and unfortunately D_North_American_1983 doesn't match
any of them.  One solution is to use a form with a more recognisable
nad83 datum like:

  -a_srs '+proj=utm +zone=18 +datum=NAD83'

or you can file a bug against the ECW driver and I can improve it's rules.
I really need a more centralized method on the OGRSpatialReference that
drivers can use to recognise common datums, such as this.  Having bits
of logic in many drivers that tries to recognise stuff like NAD83 is crazy.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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