Ai meshes are very easy to make. In fact, they are the only things I've
learned to create with 3dmax. I had to learn how to path out the tunnels in
Cedar Fall. I'm sure there are many wayt to do this. Here is the quick and easy
1) Import the standard mesh you want to create the aimesh for.
2) Turn on 2d snap, right click on the 2d snap button and click on clear all.
3) Select splines in the create toolbar and create a line.
What you are shooting for at this point is a surface that will intersect the standard mesh just above the ground for any area you want pathed. The tunnels in Cedar fall were very large, so I started out by outlining a portion of the tunnels from the top view, making sure there was a vertex for ever place the standard mesh that had a change in height. Ai meshes for simple objects, like a story buildings, can be created using planes, but the tunnels were complex, so the surface I created for them was composed of triangles. It this point I had created an flat outline of a portion of the tunnels. Now to add the rest.
4) Right click on the 2d snap and check the vertex checkbox.
5) In the modify toolbar, go down to the geometry pull down and click on the Create Line button.
When the cursor is over an existing vertex, it will turn blue. That's what you want. Click on an existing vertex and add lines so that you've finished outlining your standard mesh and the spline is entirely composed of triangles. Now it's time to convert it into a surface. The spline should still be flat at this point.
6) Select surface from the modifier list, set patch topology steps to 0 and flip the normals.
7) Right click in the active viewport and convert the surface to an editable mesh.
8) In the Modifier toolbar, click on the + sign in from of the Editable Mesh and select vertices.
9) Select and adjust the height of each vertice so that the surface intersects the standard mesh, just above ground level, for the entire standard mesh.
It's time to add the material to the surface. Since I'm not well versed in 3dmax, I stole the material from another aimesh. When I did this, I notieced that the submaterial from the import aimesh had been named after the standardmesh with '_Material0' tacked onto the end of the name. I changed that to match the name of the standardmesh I was creating the aimesh for, then added that materail to my surface.
10) Rename the surface to COL01
11) Clone the surface and rename it to LOD01
12) Delete everything accept those 2 surfaces
13) Export to a standard mesh, making sure that 'use object names for ?' is checked and 'create lods' is not checked.
The exported mesh should have the same name as the standard mesh, accept instead of ending in '_M1', it should end in '_A1'.
14) Finally, if the aiMeshes folder does not exist in your games root folder, create it and place your aimesh and rs files into that folder.
Now you can create your pathmaps. There are many ways to create aimeshes with 3dmax. The surface does not have to be contiguous. CajunWolf like to use planes, which work well when the standardmesh is fairly level. The tunnels in cedar fall were not, so I had to come up with another method. When multiple planes are used, you can combine them into on object by selecting one of them and attaching the others to it. This is done by select 'Attach' from the geometry pulldown in the modifier toolbar.
Much can be learned from openning an existing aimesh in 3dmax. Bridges, for example, tend to have vertical planes that account for guardrails.