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Contents, Programmers Guide, World Representation, 2D Content Processing, Non Manifold Resolution

Non Manifold Resolution

PathEngine's internal mesh format supports configurations such as in the following image:

Here a terrain surface is broken by a single edge with two vertices, with a ramp connecting to the same two vertices.

This configuration is useful, for example, for connecting the internal parts of buildings to a terrain, requiring only a minimal 'portal' edge to be cut into the terrain.

In the internal mesh format there is no problem with this kind of configuration, because connections between faces are specified explicitly.
When processing content in the form of face/vertex meshes, however, connections are implied by the fact that pairs of vertices are shared across a connection.
When exporting the mesh shown, the content processing would therefore normally complain about a 'non-manifold' edge, i.e. an edge that connects to more than one other edge.

An explicit connection resolution step is performed, therefore, in order to resolve the connections at these kinds of portal features.
Specifically, connections that would not encircle a vertex are preferred over connections that would.
So the connection shown by the blue arrow in the above image will be chosen in preference to connection across the surface under the ramp.
In practice the result is that agents will be able to move up the ramp from the terrain surface, as desired. Movement in the direction shown by the red arrow will be blocked by the back edge of the portal.

Documentation for PathEngine release 6.03 - Copyright © 2002-2021 PathEnginenext: 2D Content Processing Options