[gdal-dev] building geotransform with lower left and upper right coordinates

Brice Lambi lambi at ucar.edu
Mon Feb 13 13:39:02 EST 2012

Hi Brian,

Thanks for the help, you were correct that I just needed to inverse my 
dy value in the geotransform.


On 02/13/2012 10:44 AM, Brian Case wrote:
> Brice,
> After some thought your image might not be bottom up. if thats the case
> calc the origin the way you did before, but don't convert back to lat
> lon
> Brian
> On Mon, 2012-02-13 at 05:40 -0700, lambi at ucar.edu wrote:
>> Hello,
>> I have a raster where I know the projection and the lower left and upper
>> right coordinates and pixel size but I don't know the upper left
>> coordinate.  It is a lambert conformal conic projection:
>> "+proj=lcc +lon_0=95W +lat_0=25N +lat_1=25N"
>> where the lower left is -113.1333, 16.3691
>> upper right is -49.385, 57.289
>> dx/dy is 1015.875 (m)
>> width/height is 5120
>> I've tried transforming the lower left lat/lon to lcc projection, adding
>> dy*height and then converting back to lat/lon (and a few variations of
>> this) but I can't seem to get a proper answer for what the upper left
>> should be so I can build a proper geotransform for this dataset.  I've
>> tried adding two GCPs for these points but gdalwarp says it doesn't have
>> enough points to complete the warp.
>> How can I find the upper left with the given information so I can build
>> the geotransform?
>> Any help is greatly appreciated!
>> Brice
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