Camera Tracking - Getting Actor Feet to Match Floor

Hello all,

I’m using one of the free green screen plates from that site “Hollywood Camera Works” to practice camera tracking for matchmove. I’ve built a simple room to place the actor in. I’m able to get a solve error under 0.3, and the final composited scene (actor over 3D environment) looks relatively nice.

The only problem is that the floor seems to be moving slightly faster than the actor’s feet, and I can’t figure out why. I’ve tried a couple things to no avail: varying “set scale” settings, setting a scale for the mapping node just before image texture nodes.

The floor seems to go faster than the actor’s feet at the same rate no matter what.

Any suggestions? Typical “gotchas” I need to look out for?

Try calculating the FoV of the shot and match the Blender camera to that

Your floor object is not on the right height is the most probable cause if solved trackers themselves stick to plate.

Sorry, I’m a newbie. How do I calculate the FoV? Are you referring to the sensor size + lens focal length? I’ve found the sensor size for the test footage used, but was unable to find the exact focal length. Blender seems to have guessed the focal length as 5.61mm, which I feel is weird, but doesn’t look terribly odd in the final render.

Hmm good idea. I’ll look into that.

I just had a thought. Once I use the “set floor” function, am I no longer allowed at that point to change the camera’a Z position? I’ve been doing that and now wonder if that was the problem. Currently I’m re-rendering another test where I left the Z position alone, but did transform using X+Y, plus Z-Rotation to try and orient the tracked camera correctly in my scene.

Should I instead be rotating my scene or something?

The camera should end up roughly correct from the default scene. If not then you probably have a bad solve from your track

That 5.61mm is definitely wrong. From the camera view with your footage as a background, start scrolling that the lens size until things start to match up

I just wanted to come back and say thank you to everyone who gave advice. It ended up totally being the Z transform. Once I stayed away from altering the Z transform of the camera after using the “set floor” functionality, the floor began to line up perfectly (well… almost… but still only as bad as my actual track).

El Director - Yeah, I agree about the lens. Do you know how to ask blender to solve for what the focal length is? I don’t have that information, so just stopped trying to guess.

(but yeah, problem solved … yay)