[gdal-dev] Geotransform for non-North-up images?

[jratike80]

Hi,

The geotransform parameters are the same than in the ESRI wordfile. I tried
once to understand how the parameters behave when the image is rotated and
wrote an OpenOffice spreadsheet about that. You can have a try and play with
the parameters. I hope I have understood it right. I was not so sure myself
and therefore there are some unnecessary cells with forward and backward
formulas just to verify the results. 

http://latuviitta.org/documents/rotated_worldfile.ods

-Jukka Rahkonen-


G Seiffert wrote
> Hi all from GDLA.
> 
> Thanks for the opportunity to as a question. It's regarding the 
> Geotransform 
> Tutorial(https://gdal.org/tutorials/geotransforms_tut.html). Tried to 
> get info in the web but since this seems a tricky one, my searches failed.
> 
> The tutorial only deals with the ideal case of 'North up' images, for 
> which GT(2) and GT(4) are zero. However, my images are 'East up' and 
> potentially 'any direction up' (underwater photomosaic surveys by ROV). 
> The rotation works with '90' for GT(2, 4). But the scaling seems 
> completely ignored. Any hint? If it would be easy, I assume your 
> tutorial would give an example for how to deal with "non-N-up' images, 
> but ...
> 
> My pics are 1920x1080, with pixel resolution of 0.0015 (yes, 0.15cm per 
> pixel, we're flying just 3m above the bottom).
> 
> In case I rotate the images prior to geotransform (in Photoshop), 
> geotransform works perfect, with GT(2, 4) = 0. Scaling spot on. I can 
> live with that for our last survey but I'm also looking for a solution 
> in case our survey heading cannot be 0, 90, 180, or 270, but has to be 
> something like 35° (due to bottom currents etc.).
> 
> Best regards, any hint qappreciated,
> Gerhard
> 
> 
> 
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