# [gdal-dev] geotransform rotation and gdal_merge

Chaitanya kumar CH chaitanya.ch at gmail.com
Sat Jul 21 07:46:06 PDT 2012

```Dave,

You said that you have lat/lon values for each pixel. Can you explain?

On Fri, Jul 20, 2012 at 8:44 PM, David Hoese <dhoese at gmail.com> wrote:

>  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
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>

--
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20120721/c1915585/attachment.html>
```