[Gdal-dev] Re: GDAL and Spot Vegetation

[Markus Neteler]

On Wed, Aug 18, 2004 at 01:07:10PM -0400, Frank Warmerdam wrote:
> 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

No doubts (I was aware of both the name - looking into the Evenden docs
as well as the url). 
But I wasn't aware of 'testepsg' - thanks for the hint. Exactly what
I was looking for.
 
> 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]]
> ...

[for other users a note:
   cd ogr/ ; make testepsg
compiles it 
]

> 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. :-)

..."use the PROJ.4 string to describe an SRS"... excellent!

So no more excuses to write the proper VRT file :-)

Thanks for all your helpful comments.


 Markus