Collision between a 3D object and ViewingPlatform

Hello anyone,
I make a first person shooting game,I use “PlatformGeometry object” to make a Gif picture
on the ViewingPlatform side.
How can I detect the collision between the Gif
and other 3D objects in the scene,or detect
the collision between ViewingPlatform and 3D object.
anyone can help me?
thank you very much!!!

Here is a good resource …
http://j3d.org/tutorials/collision/index.html

Thank you very much!!
I can get some idea from the tutorials,
I will try to solve my problem.