Layer-Based Collision Detection.
Layer-Based collision detection is a way to make Game Objects collide with another specific Game Objects that are tied up to specific layers.
In the image above you can see 6 GameObjects, (3 planes, 3 cubes) and the “Collision Matrix” to the right that states which Objects can collide with which layer. In the example, we have set the Collision Matrix in a way that only GameObjects that belong to same layers can collide.
Setting GameObjects to detect Collisions Based on Layers.
Select a layer your Game Objects will belong to
Repeat 1 for each Game Object until you have finished assigning your Game Objects to the layers.
Open the Physics Preference Panel by clicking on Edit->Project Settings->Physics.
Select which layers on the Collision Matrix will interact with the other layers by checking them.
