[gdal-dev] gdalinfo: Corner Coordinates

Frank Warmerdam warmerdam at pobox.com
Tue Feb 15 13:20:24 EST 2011


On 11-02-15 07:50 AM, Emilio de Torres Fernández wrote:
> If I use the equations of the azimuthal equidistant projection <http://> to
> transform long=6d32'32.13"W and lat=36d42'16.93"N) I get x = -0.65688 and y =
> 0.78961, not (-4195457.112, 5006607.739). Why??? I guess I misunderstood some
> concept of the "Corner Coordinates" of gdalinfo.

Emilio,

Well, I don't know what equations you are using, but I can't imagine getting
x and y values in meters that small unless you were *right at* the origin
which is not the case.  Perhaps you don't understand the units required by,
and/or produced by the equations you are applying?  When I use PROJ.4 to
do the reprojection (as GDAL does underneath) I get:

cs2cs -I +proj=aeqd +lat_0=-6.2500000000005 +lon_0=36.5166666666677
   +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
   +to +proj=latlong +datum=WGS84
6d32'32.13"W 36d42'16.93"N
-4196092.49	5007369.96 0.00

Make sure you aren't mixing up longitude and latitude.  GDAL and PROJ.4
default to long/lat order while the location seems coincidentally near
the origin of the projection *if* you reversed the ordinates.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent



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