3D Scene
The “scene” (also called a 3D scene in other sections of the manual) is a large array of three-dimensional triangles that compose a larger environment that will be used in a simulation. The Objects exist within the scene.
Grouping
While scenes are initially composed of three-dimensional triangles, the scene has materials assigned to it in “groups”, that is, groups of triangles that are determined to be related to one another.
For instance, a wall in a room with some kind of hole for a door and window would look like one continuous flat surface in the real world, but digitally it would be composed of a lot of triangles. When importing a scene, Impulse analyses the 3D geometry and groups triangles together that have the same initial material, are touching one another, and have similar normals (i.e. are facing the same direction).
When assigning materials to the scene, as opposed to assigning individual triangles, the larger abstract groups are assigned instead. This is more convenient than having to do all triangles manually.
Assignment
At the lowest level of the scene, each triangle has a material ID assigned to it that can either be done automatically when imported, or manually.
If automatic assignment is specified when importing a 3D scene, Impulse will look at the material names assigned to the 3D geometry and perform textual analysis to determine which of the default materials would be the best fit for different parts of the geometry. The materials will then be created and assigned to the applicable geometry groups.
If no automatic assignment is done, then the user can assign geometry to the groups manually. When in the materials tab, the user can either select groups by clicking them individually, or adding them to a larger selection by shift clicking or dragging a box around the desired geometry. The selection positions can either be specified to be the center point of the groups, or having it so that clicking anywhere in the group will select it.