When I want to calculate the volume of a building polygon (in my case), do I use the GSD that I received in a WebODM report or the pixel size of the elevation raster? What is the difference between the two (why is pixel size lower than GSD?)?
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1 Answer
The ground sampling distance (GSD) is the measure of the land units per pixel and is a function of the sensor size, the camera focal length, the image size, and the height of the drone above the land surface. You might expect the GSD to vary per pixel on any drone flight image because the drone is probably flying at a fixed altitude but the underlying terrain is fluctuating in elevation.
The spatial resolution of the resulting surface model would refer to the dimension of the cell size representing the area covered on the ground regardless of the GSD of the input images.
To measure the volume of the building you would use the spatial resolution of the resulting surface model produced by WebODM not the GSD.
FYI, you can alter the default surface model spatial resolution in WebODM. See this link for more help.
