In this example set extensions have been created in Photoshop and imported in AE as a new composition with a left and right side extension to our castle wall.
Open the original composition with the movie file and the composition containing the layers from Photoshop.
Nulls needs to be created on the master composition to give you the data required to attach the new layers to.
If you haven't already, add the 3D Camera Tracker to the .mov layer. This will give you the markers you need to create a Null.
If you don't see the markers, highlight the layer, select the Effect Controls panel and click on the 3D camera tracker effect.
Select a group of markers on each side of the castle wall, right click and select Create Null.
Go to the composition with the additional layers, highlight a layer, copy and paste it into the master composition and make sure to place it at the top of the layers.
Make sure that you make the new layer 3D.
You then need to copy the Position data from the Null which matches the side of the castle wall you are working on, and copy this data to the New Layer position data. Then rescale and reposition the new layer as needed.
You should end up with the additional wall extensions in place and attached to the original castle wall when the .mov file plays back.
Written by LA