[gdal-dev] geotransform rotation and gdal_merge
dhoese at gmail.com
Fri Jul 20 08:14:21 PDT 2012
I'm attempting to put aircraft scan data into geotiffs (1-3 scanlines
each) and then use gdal_merge.py to combine them into one large geotiff
that has the entire aircraft's path. The scan lines are 15 pixels wide
and taken every 10 seconds, the geotiffs are wgs84 lat/lon, and I have
lat/lon values for each pixel. To handle the case when the aircraft
isn't flying straight north I think I have to use the 2 rotation
parameters in the affine geotransform, is that right? I don't have any
test cases, but I think if I don't use rotation anything that reads the
geotiff will think that the image is square(aligned) in lat/lon space.
Whether or not I need to use this, can someone explain to me how to use
the rotation coefficients? What are the actual values of the
coefficients supposed to be? I couldn't find a good example and I
couldn't get any basic situations to make sense, like a 2x3 array turned
45 degrees. I used these equations:
Xgeo = GT(0) + Xpixel*GT(1) + Yline*GT(2)
Ygeo = GT(3) + Xpixel*GT(4) + Yline*GT(5)
And lastly, does gdal_merge.py handle rotation? I checked the source
and it doesn't ever seem to use elements 2 and 4 in its calculations.
Thanks for any help.
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