I am using ORB-SLAM3 with a monocular camera on a drone for Augmented Reality application. I need to know the absolute scale of the map formed by the SLAM.

I cannot use a stereo or RBG-D setup. Tthe scale of the monocular SLAM is defined every time the SLAM is started. Can someone please suggest any ideas how can I get the scale factor/ absolute scale of the map?

Can GPS be used to do this? To measure the distance between points in GPS co-ordinates and the corresponding distance in SLAM map and just divide those to get the scale factor?


GPS is a good idea. Draw a trajectory using the GPS and align/scale it to your slam trajectory. But if your drone movement is small (few meters) it is not a solution.

Or you can just put a scale known object in the scene around the initial position. By comparing the reconstructed size of the object and the actual object size, you will find the scale factor.


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