[gdal-dev] geotransform rotation and gdal_merge

[David Hoese]

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.

-Dave
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20120720/db0e3414/attachment.html>