[gdal-dev] Reading the data 'backwards'

tasmith3 at rockwellcollins.com tasmith3 at rockwellcollins.com
Fri Nov 20 11:10:54 EST 2009

I work with code that handles data in a particular way.  Instead of using 
the top-left corner as the origin, it uses the bottom left.  It treats the 
data as if it's sitting in quadrant 1 on an X-Y plane with the bottom left 
corner sitting on the origin.  The code expects me to read in the data 
from the file starting with the 'first' row (the bottom row) to the top 
row (the 'last' row) from left to right.  If my image has n rows and m 
columns, could I do something like this...?

RasterIO( GF_Read, 0, n, m, n, ...)

and would GDAL be smart enough to know that since I'm placing my origin at 
the bottom left corner, it needs to read backwards or 'up' the image?  If 
it can't, that's ok - I'll just have to do some post processing on the 
output buffer after the read.  Changing the code around so it treats the 
top left corner as the origin isn't an option.  I don't have that kind of 
authority and it'd be a massive change.


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