[Gdal-dev] Warping Plate Carree images to Mercator

[Joaquim Luis]

Robert,
I don't know what you got, but I know that you cannot project the poles 
using a Mercator projection
(+/- 90 degrees are infinitely  deformed  in  Mercator)

Joaquim Luis
 
> Howdy folks!  I'm super-new to GDAL and the whole GIS space.  I've got
> a question that I think is pretty simple...
>
> I'm trying to warp the NASA BlueMarble images into Mercator WGS84
> projected images.  The documentation on BlueMarble says that they come
> in the Plate Carree WGS84 projection system.
>
> For starters I'm trying to take the lowest-resolution 8km whole-world
> image and convert it into a 512x512 GeoTIFF in Mercator.  Below is my
> best guess so far as to how to do this with the gdal command line
> utilities:
>
>> gdal_translate -a_srs EPSG:32662 -gcp 0 0 -180 90 -gcp 5400 0 180 90 
>> -gcp 5400 2700 180 -90 world.jpg world.tif
> Input file size is 5400, 2700
> 0...10...20...30...40...50...60...70...80...90...100 - done.
>
>> gdalinfo world.tif
> Driver: GTiff/GeoTIFF
> Size is 5400, 2700
> Coordinate System is `'
> GCP Projection = PROJCS["WGS 84 / Plate Carree",GEOGCS["WGS 
> 84",DATUM["WGS_1984"
> ,SPHEROID["WGS 
> 84",6378137,298.2572235630016,AUTHORITY["EPSG","7030"]],AUTHORITY
> ["EPSG","6326"]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORI 
>
> TY["EPSG","4326"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","32 
>
> 662"]]
> GCP[  0]: Id=1, Info=
>          (0,0) -> (-180,90,0)
> GCP[  1]: Id=2, Info=
>          (5400,0) -> (180,90,0)
> GCP[  2]: Id=3, Info=
>          (5400,2700) -> (180,-90,0)
> Metadata:
>  AREA_OR_POINT=Area
> Corner Coordinates:
> Upper Left  (    0.0,    0.0)
> Lower Left  (    0.0, 2700.0)
> Upper Right ( 5400.0,    0.0)
> Lower Right ( 5400.0, 2700.0)
> Center      ( 2700.0, 1350.0)
> Band 1 Block=5400x1 Type=Byte, ColorInterp=Red
> Band 2 Block=5400x1 Type=Byte, ColorInterp=Green
> Band 3 Block=5400x1 Type=Byte, ColorInterp=Blue
>
>> gdalwarp -s_srs EPSG:32662 -t_srs "+proj=merc +datum=WGS84" -ts 512
> 512 world.tif worldm.tif
> Processing input file world.tif.
> :0...10...20...30...40...50...60...70...80...90...100 - done.
>
> The end result is definitely a 512x512 file that's been warped, but it
> doesn't look at all like a Mercator projection of the Earth.
>
> Any help would be greatly appreciated!  Thanks!
>
> -robert
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