Analyzing the Character Mesh Using STL Check

I'm doing this chapter by example because I don't know exactly what errors your mesh might have or what adjustments might be required. I'm constantly creating new subobjects (vertices, edges, faces, and polygons), moving things around, knocking out polygons, and attaching and detaching elements. All these operations inevitably lead to some type of simple geometrical error that you can quickly expose with an STL Check modifier. You can discover other errors such as crossed edges by adding a checkerboard texture map to the character, after you've created the UV map, and observing any weird distortions on the texture. (See the next chapter for information on adding a checkerboard map.) You can fix all these errors fairly easily, usually by capping holes, creating new polygons, and moving or welding vertices.


STL stands for Stereo Lithography, which is a file format that enables a computer to drive a laser that will build a 3D model from scratch, based on an STL file. If the STL Check modifier in 3ds Max finds errors, the computer-laser system can't properly build a 3D model. If your mesh's geometry passes this check, most likely a game engine can render the mesh without crashing.

To quickly check all the errors in your mesh, first save your scene to a MAX file because you have to reload it after this step. Select one mesh object in your scene, such as the torso, and in the Modifier panel, click the Attach List button to the right of Attach. Select all objects in the list that represent the entire character, and click Attach. You should now have a single mesh entity.

Then right-click the mesh, and at the bottom of the quad menu, select

Convert To Editable Mesh. In the Modifier panel, add an STL Check modifier. In this modifier's options, make sure the option Everything is selected, and click Check at the bottom (see Figure 4.1). Press F3 to toggle between solid and wire frame modes. In wire frame mode, note the errors highlighted in red around the mesh. (My mesh had just over 600 errors.) Don't be frightened by this; fixing one problem area, like a single bad polygon, usually corrects a multitude of errors at once.

Figure 4.1 With all elements of the mesh attached, add an STL Check modifier to the stack to view errors in your mesh. (Mine are highlighted in red.)

You can view the errors by category by selecting the following in the STL Check modifier's options:

■ Open Edge. Indicates an object—either an element or a polygon—that is not closed. For instance, if you created a simple Sphere primitive and then deleted a face or polygon, the STL Check highlights all edges around the open area. You typically resolve this by creating a new polygon or adding a Cap Holes modifier.

■ Double Face. Indicates that the vertices defining the triangle that constitutes the face actually consist of multiple vertices per vertex position. If you enter Vertex Edit mode and click+drag on what appears to be a single vertex, the Modify panel shows more than one vertex selected. Many times you can resolve this by selecting these vertices and clicking on Weld, which welds them into a single vertex. If Weld does not resolve the problem, you must delete and re-create the faces or edges in that area.

■ Multiple Edge. Indicates two or more edges occupying the same space. This is similar to the Double Face error. You resolve it by welding vertices or deleting edges and creating new polygons.

Clicking on Selected Edges in the STL Check modifier shows only the edges of polygons that have the problem. This helps clarify the areas on which you need to focus.

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