[Gdal-dev] Re: GDAL and Spot Vegetation

[Frank Warmerdam]

Markus Neteler wrote:
> On Wed, Aug 18, 2004 at 12:28:35PM -0400, Norman Vine wrote:
> 
>>Vincent Schut writes:
>>
>>>About Plate Caree, I'm not sure either. I used a simple lat/long wgs84 
>>>configuration which looked OK. It is however possible that better projection 
>>>parameters exist... 
>>
>>"Plate Caree" is just another name for "Equidistant Cylindrical"  Projection
>>i.e. linear scaling of latitudes and longitudes
>>
>>In other words, all meridians and parallels are straight lines. 
> 
> 
> How should I write that as SRS OGC WKT? 
> While I have addressed the wgs84 things, the projection info is somewhat
> missing. So far I didn't find any example.

Markus,

Norman is right about Plate Caree.  It is also known as Equirectangular in
some circles.  The page I maintain about it is at:

   http://www.remotesensing.org/geotiff/proj_list/equirectangular.html

The "testepsg" program from gdal/ogr says:

warmerda at gdal2200[25]% testepsg '+proj=eqc +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0'
...
PROJCS["unnamed",
     GEOGCS["WGS 84",
         DATUM["D_unknown",
             SPHEROID["WGS84",6378137,298.257223563]],
         PRIMEM["Greenwich",0],
         UNIT["Degree",0.017453292519943295]],
     PROJECTION["Equidistant_Cylindrical"],
     PARAMETER["latitude_of_origin",0],
     PARAMETER["central_meridian",0],
     PARAMETER["false_easting",0],
     PARAMETER["false_northing",0]]
...

A recent update (just last week) in the VRT format driver allows use of any
"user input" for describing coordinates systems.  That means you should (with
recent CVS builds) be able to just use the PROJ.4 string to describe an SRS
if you want.  If not, just embed the WKT with all the yucky XML escaping.
Actually, come to think of it, there likely aren't any XML escapes actually
required for WKT in VRT XML though by default VRTs produced by GDAL will apply
all possible XML escape sequences .. not just the required minimum.  Now I am
getting off topic. :-)

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