Flattening the cloud

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proteus
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Flattening the cloud

Post by proteus »

Hi!

I am looking for a way to flatten (not normalize) the cloud generated in Metashape from UAV images.

I would like to run analyses on photogrammetry cloud but before that I checked it vs ALS cloud available from public sources. It turned out that areas closer to the edges of the cloud are slightly bent (quite common issue) and I'd like to straighten it in Z axis using CC. I ran C2C tool and generated scalar field which clearly shows which areas require attention, and which ones are ok.

Is it possible to fix the issue using cloud algebra and new scalar field which potentially can be used as a input with information which part of the cloud should be moved in Z axis? If it would be doable, can You provide me any tips how to approach this challenge?

Thanks in advance!
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Re: Flattening the cloud

Post by danielgm »

Hum, it looks challenging to me... You could use the 2.5D Volume calculation tool to compute the 'height difference' scalar field (but on a gridded cloud, so you would have then to interpolate this SF back to the original cloud). And then add or subtract it with the original Z coordinate converted to a SF (via the SF Arithmetic tool indeed).
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Re: Flattening the cloud

Post by smacl »

Any idea what is causing the error? Problems near edges are sometimes due to bad projection or incorrect scale factor. If you had enough known control to compare against, you could try a 7 parameter Helmert transformation to bring it back to your project grid. Alternatively, within your photogrammetric software, project from WGS84 to ECEF and the 7 parameter into your project grid.

Haven't used CC but guessing it links into PROJ which allows you to do all this kind of stuff.
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proteus
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Re: Flattening the cloud

Post by proteus »

Hello!

Thanks for your suggestions! Till now I was not able to fix the error but still working on it.

Lightly dome shaped PC is a typical feature of photogrammetry process with not compensated rolling shutter effect. I was not making the flight or even processing the data, only trying to squeeze as much as possible out of them.

Hoped that maybe 3D Forest INventory plugin in 2.13 will help me with normalizing the cloud, but I am not there yet... Still trying to figure out how to make the plugin work with the UAV Photogrammetry PC where I have only trees canopy, patches of ground but no stems...

I've got some ideas still, how to bite it!
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