Thanks Javier. Need to confess: math is not my strong side. I'm more the
"trial and error" guy. And - shame on me - Google.
Got the rotation AND the scaling correct meanwhile, calculating the
params as described here:
https://gis.stackexchange.com/questions/69715/rotating-rasters-using-gdal-geotransform-and-arcgis-desktop?noredirect=1&lq=1
Below a code snippet (I work in Python). However, with the exact calcs
from above website, my pics were rotated correctly but for some strange
reason mirrored vertically! Try and error: Making GT(4) negative got rid
of the mirroring. So almost happy now, just facing a weird shift of 2m
to west and 0.7m to south, working on it.
# ROTATION PART Start ================================================
rot_deg = 90
rotation = np.deg2rad(rot_deg)
GT0 = orig_x
GT1 = math.cos(rotation) * image_resolution
GT2 = -math.sin(rotation) * image_resolution
GT3 = orig_y
GT4 = -math.sin(rotation) * image_resolution
GT5 = math.cos(rotation) * image_resolution
geotrans = (GT0, GT1, GT2, GT3, GT4, GT5)
# ROTATION PART End ================================================
Thanks so far! Also Thomas and Jukka!
Gerhard
Javier Jimenez Shaw <mailto:[email protected]>
21 December 2020 10:55
Those transformation parameters can be seen as a 3x3 transformation
matrix like this
Xg GT1 GT2 GT0 Xp
Yg = GT4 GT5 GT3 * Yp
1 0 0 1 1
Where [Xp, Yp] is the coordinate in pixels, and [Xg, Yg] is the
"geographic" coordinate (whatever it means ;)
the 2x2 top left corner of the transformation matrix can be seen as a
2D rotation-scaling matrix:
https://en.wikipedia.org/wiki/Transformation_matrix#Examples_in_2_dimensions
[GT0, GT3]is the "geographic" coordinate of the pixel [0,
0](regardless rotation or scaling)
Cheers
.___ ._ ..._ .. . ._. .___ .. __ . _. . __.. ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.
G Seiffert <mailto:[email protected]>
21 December 2020 10:24
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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