Adjusting from ellipsoidal to orthometric heights

General Help
#1

Hello,

For some maps I would like to fly without GCP’s, which means I will need to try and adjust from ellipsoidal to orthometric height.

Does everyone just do this after the photogrammetry stage with QGIS/GDAL? Are there any advantages to somehow adjusting the elevation data in the image tags prior to photogrammetry?

When adjusting, do most people just use a constant value? Does anyone use a geoid grid file for large projects?

For conventional surveying/mapping our survey software just lets us select the correct geoid file, which is HT2-2010. But I don’t actually understand what happens behind the scenes and how I might implement a consistent process with RTK drone mapping.

Thank you for any suggestions

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#2

The pointcloud can be adjusted pretty easily in CloudCompare, with DSM you could use the raster calculator in QGis.

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#3

I do both. When adjusting the photos I use this free tool which does an x/y lookup for each one and applies the offset:

https://www.seilergeodrones.com/geophoto-latest

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#4

Good tips, thank you.

I hadn’t checked out raster calculator yet and looks like that is a functionally of QGIS that I will needing to implement for various things.

I ignored GeoPhoto because for some reason I believed I would not be able to use it with my required geoid model. I will be testing this as soon as I can get it installed on my work machine.

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#5

In cloudcompare you can make DSM/dtm and “ortophoto” from a pointcloud.

So you could adjust the cloud and then extract what you need.

#6

Could the developers add an option/parameter to ODM which is equal to the correction offset from ellipsoid to orthometric height?

Let’s say the offset for Project Area XY is -50m. This value just needs to be added to the Z-data in point cloud/DSM/DTM. This way one would not need to post-process the elevation data.

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