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Author Topic: Defining vertical datum when exporting point clouds  (Read 184 times)

ivan-zd

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Defining vertical datum when exporting point clouds
« on: September 05, 2022, 05:24:16 PM »
Hi,

When exporting the point cloud using exportPoints() function I can define only the output CRS but not the vertical datum as well. Is there any possibility to define the vertical datum (using EPSG ideally) so that it's also written to the header of the LAS/LAZ file?


Paulo

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Re: Defining vertical datum when exporting point clouds
« Reply #1 on: September 05, 2022, 05:49:01 PM »
Hi Ivan-ZD,

you just need to define the CRS that includes your geoid. Supposing your chunk crs is already defined with geoid then you coud just do:

Code: [Select]
crs = chunk.crs
chunk.exportPoints(...,crs=crs,...)

Hope this gets you along the way....
Best Regards,

Paul Pelletier,
Surveyor

ivan-zd

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Re: Defining vertical datum when exporting point clouds
« Reply #2 on: September 06, 2022, 11:53:44 AM »
Hi Paulo,

Thank you for your reply. I will try once with geoid file but I'm afraid it won't be good approach for me on the long run as I was hoping for rather generic approach where I could just define EPSG code and that it's then written to the header of the LAZ file. The reason behind is that I need to have LAZ file with this vertical datum info when I pass it over to Cesium ION for tiling because otherwise Cesium assume that heights are relative to ellipsoid height and it's not fitting the globe.

I see PDAL can help with setting correctly vertical datum info but I was hoping I could do that directly in Agisoft to avoid additional steps.

Anyway, I'll look more in details there, thanks again for your answer.


Best regards,
Ivan

Alexey Pasumansky

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Re: Defining vertical datum when exporting point clouds
« Reply #3 on: September 06, 2022, 03:34:52 PM »
Hello Ivan,

If you need to export the dense cloud in the compound coordinate system that uses height above geoid, the corresponding coordinate system definition should be passed to the export task (can be loaded from external PRJ file or as a string variable) and also the corresponding geoid file should be initialized in the code using addGeoid function before any operations for the related coordinate systems are applied. Instead of geoid file, however, you can use fixed offset defined via crs.geoid_height method.
Best regards,
Alexey Pasumansky,
Agisoft LLC