Nothing stops you from scaling your footage until it's only a tiny speck surrounded by sand. Otherwise if you really want to have it ultra realistic you have to re-create the whole shot as CG animation like they do on movies. There simply is only so much you can do with a drone and some static footage. You could of course try to find matching shots of a desert or create them yourself. Just as much as this is a compositing problem, this is also a problem of planning your shots and gathering the necessary footage.
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Thank you so much Millenium, I just received the footage from the director.
Let me be clear now with what i see with the footage.
what I meant is that a drone is flying out of the stadium into the sky revealing the stadium's exterior as the shot gets wider in a 45 degree angle.
All they need is to remove the exterior which is mostly trees and highways and replace them with a packed city.
I need to place the city around this stadium without jeopardizing their original camera movement.
So Szalam, this is what I am exactly looking for
You will want to use a 3d camera tracker of some kind and place 3d models of a city into the scene. If you are mostly just familiar with After Effects, great! There's a 3d camera tracker built into it. I'd probably recommend Video Copilot's Element 3d plugin and their Metropolitan pack for building the city.
I would probably use stabilize motion and then select scale and rotation. This should keep the stadium the same size throughout the composition and allow you to create a track matte. Then it's just a matter of removing the stabilize motion and adding that movement to the track matte layer. I have an animation preset did I created for that exact task that I will happily share with you if you want to try that approach.
This all depends on the footage. Camera tracker may work better, but the only way for me to pick the most efficient solution is to see the footage.
The most important part of any solution is to only work on the frames were you actually have to remove the background. There is no advantage at all to tracking something and creating a mathe for frames you will never use.