I mapped an area with WebODM (default options) based on images taken from a phantom 3 pro 2.0. The dsm shows elevations that are about 80m lower than correct values according to survey maps/google maps.
Based on searching the forum for similar problems, there is consensus that standard GPS altitude values are not accurate. However, that doesn’t seem to be the issue. I checked the exif data of the images and the drone’s recorded GPS altitude has near perfect accuracy. Also the drone took the photos from 80m above ground. It is as if the drone records the elevation at ground level while webodm assumes the drone records the camera’s elevation. This is my first use of both the drone and the software so my understanding of this issue is probably lacking. Hoping to hear from those with better knowledge.
I tried adding GCPs and ODM choked on them. But the problem for me is I get excellent RTK data, almost perfect on all axes, and the resulting map is accurate except the elevation that seems to be a quite simple misinterpretation by ODM. I was hoping that this is something that can be easily fixed.