Once you have the two surfaces, how do you figure out which vertices correspond to each other? Do the two meshes need to have the exact same polygon structure?
@HelloWorld Typically they're just modeled this way. The artist makes some initial mesh (as in Scotty3D/A2) and then tweaks the vertex positions a bit for each blend shape (…as in Scotty3D/A2!). This way, you don't have to figure out the correspondence (which is quite challenging in general).