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Unmanned Spaceflight.com _ Image Processing Techniques _ Chandrayaan 2 TMC 3D modelling

Posted by: threadworm Jan 8 2023, 08:55 AM

I have a question about constructing 3D models using the latest TMC data. I've tried using QGIS (and also Blender) to generate them using the DTM-OTH pairs available, and it seems that the only way a sensible looking model can be geneated is by reducing the Z axuis exaggeration by something like 0.00025. I'm using the QGIS2threejs plugin, and that multiplication value is pure guesswork based on "what looks right".

Does anyone have an explanation as to why the original geotiffs have such a huge vertical displacement, or a way of working out what the exact value should be? Attached are images showig the original and adjusted values for a pass covering the Descartes region.

Posted by: John Moore Jan 10 2023, 11:02 PM

There is some information concerning this 2012 paper https://www.researchgate.net/publication/234698337_DEM_Generation_for_Lunar_Surface_using_Chandrayaan-1_TMC_Triplet_Data , however, it is old research so don't be disappointed if the answer isn't there.

I've never used QGIS, but have generated many 3D DEMs of the lunar surface using simple 3D graphical softwares (don't ask, as there's a medley of to confuse) that can tackle PNG DEMs etc.

John Moore

Posted by: JohnVV Jan 11 2023, 03:38 PM

i do not use qgis all that much , but use Blender 3.4 all the time to make a mesh from a DEM
the exaggeration for a 16 bit unsigned tiff ( 32 bit floats seam to be broken ) is set to about 0.05 to 0.07

"Does anyone have an explanation as to why the original geotiffs have such a huge vertical displacement, "

most geo tif's are in radian / meters and are in 16 bit signed image format and for use in blender they need to be in 16 bit unsigned .

with blender it uses " blender units" the grid you see so for a good looking mesh you need to reduce the height to a rather low value - like 0.05