[gdal-dev] gdalwarp and the geos projection

[Bas Retsios]

Hi!

We use the geos projection in gdalwarp, but only as a source (not as a 
target).
The images we receive in geos projection are from the meteorological 
satellites Meteosat-8 and Meteosat-9 (MSG).
And the size of most bands is 3712x3712 pixels.

I noticed your 3700x3700 images, therefore I got curious: are you trying 
to convert back to the projection of the MSG images?

Anyway, the only suspicious part I noticed in your gdalwarp command is 
the +h=745331460 parameter.
+h is the satellite height, in meters. This "height" is the distance 
from the ellipsoid (thus not from the centre of the earth). For MSG 
(which is a geostationary satellite), the correct value is +h=35785831.
Your value is about 20 times higher, which is two times the earth-moon 
distance. Are you sure you have an image taken from that far away?
See also:
http://www.remotesensing.org/geotiff/proj_list/geos.html

Cheers,

Bas.

-- 
Ir. V. (Bas) Retsios
Software Developer
Geo-information Processing Department
International Institute for Geo-information Science and Earth Observation (ITC)
P.O. Box 6,  7500 AA Enschede, The Netherlands
Phone +31 (0)53 4874 573, telefax +31 (0)53 4874 335
E-mail retsios at itc.nl, Internet http://www.itc.nl



Andrew Chamberlain wrote:

> Hi All,
>
> Just wondering if anyone can help.  Apologies if this is the wrong 
> mailing list, but I couldn't find any other for GDAL users.
>
> I'm using gdalwarp to project an image from Plate Carree (proj=eqc) to 
> Geostationary Satellite projection (proj=geos), and I'm finding that 
> the east and west edges of the resulting Earth-disk are being cut off 
> (at the sides of the containing image).  I would estimate the clipping 
> to be ~100 pixels on each side (the overall width is 3700).
>
> The source image has the projection details given below, and the 
> command I'm using is:
>
>  gdalwarp -t_srs '+proj=geos +lon_0=0.0 +h=745331460 +x_0=0.0 
> +y_0=0.0' -ts 3700 3700 source_eqc.tif dest_geos.tif
>
> Has anyone seen this problem before with the geos projection?  When I 
> try with the ortho projection, the full Earth disk is rendered.
>
> Andy
>
> -----------------------------------------------------
>
> Size is 16384, 8192
> Coordinate System is:
> PROJCS["unnamed",
>    GEOGCS["unnamed",
>        DATUM["unknown",
>            SPHEROID["unretrievable - using 
> WGS84",6378137,298.257223563]],
>        PRIMEM["Greenwich",0],
>        UNIT["degree",0.0174532925199433]],
>    PROJECTION["Equirectangular"],
>    PARAMETER["latitude_of_origin",0],
>    PARAMETER["central_meridian",0],
>    PARAMETER["false_easting",0],
>    PARAMETER["false_northing",0],
>    UNIT["metre",1,
>        AUTHORITY["EPSG","9001"]]]
> Origin = (-20036285.350299999117851,10018754.171399999409914)
> Pixel Size = (2445.835614050000004,-2445.835614050000004)
> Metadata:
>  AREA_OR_POINT=Area
> Corner Coordinates:
> Upper Left  (-20036285.350,10018754.171) (  0d 0'0.01"E, 90d 0'0.00"N)
> Lower Left  (-20036285.350,-10017531.179) (179d59'20.45"W, 89d59'20.71"S)
> Upper Right (20036285.350,10018754.171) (  0d 0'0.01"E, 90d 0'0.00"N)
> Lower Right (20036285.350,-10017531.179) (179d59'20.45"E, 89d59'20.71"S)
> Center      (      -0.000,     611.496) (  0d 0'0.00"W,  0d 0'19.91"N)
>
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