2.5D Tracking

2.5D Tracking

You can even fake 3D parallax by offsetting layers in Z
space. Any layer that is equidistant from the camera with the
motion track points has a Z-depth value of 0. Offsetting layers
is tricky as there is no frame of reference for where they
should be placed in Z space—not even a grid .

This is what I call “2.5D tracking”: a 3D camera paired with
two-dimensional tracking points and layers. Any 3D offset
derived from a 2D track is only approximately accurate, so
this is a big cheat; if your scene has areas of frame closer or
further than the track points that you wish to match, you
can try to guess where in 3D space to place a layer and you
may just get lucky.
If your shot tracks (the camera moves), it probably requires
a real 3D camera track (see “Try It Out for Yourself” at the
end of this chapter).