The previous two modifications aimed at displaying a
single 3D model or a series of a single animated 3D model on
each AR marker. However, we can assume that there can also
be an application where each marker is shared by multiple
different 3D objects. Our third modification is for a
programmer who requires a function that switches 3D models
on each maker according to pressed keys. In this case, we are
required to modify the original sample code according to the
following points.