Camera tracking

So I have watched numerous tutorials on the camera motion tracking
and I understand the whole concept but for the life of me I cannot figure out how to make an object behind my person.

for example:
I have footage of someone with back towards camera pointing to the sky saying it’s coming.
I want to place the spaceship behind the person but can only seem to understand
how to make objects on top of my footage.

i hope this makes sense!

You must use the compositor to layer 3 items together.

  1. background vision (tracked)
  2. Rendered element (tracking applied)
  3. mask shape (possibly with tracking applied) to cut out foreground part of the vision.

The mask is used to subtract either a part of the 3D element or you can cut out the part of the vision plate and apply it on top. This creates a sandwich of video-3D-video.

Do you know of any tutorials that could further explain this

There might be some on the Tears of Steel DVD. The technique 3pointEdit is mentioning is called ‘rotoscoping’, if that helps.

Does the camera have to be moving? This is a lot easier if the camera is locked down.

1)Take a vid of the background without anyone in the shot.
2)Shoot your guy with a greenscreen (i.e. bedsheet) behind him.
3)Do your compositing using the Keying node to remove the greenscreen.
4)Fake some camera movement in the VSE to give it a handheld feel. You’ll lose some of the image size, so shoot at the highest resolution you can.

Steve S