In Houdini, geometry is made up of primitives, with the most common primitive being a polygonal faces. Each corner of a polygonal face is a vertex. To keep individual faces together as part of a surface, vertices of separate faces can be fused together as a point. When a point moves, Houdini automatically moves each of the point’s vertices as well.

• You can use vertexpoint to get from a vertex to its point.

• You can use pointvertex to get from a point to its first vertex and vertexnext and vertexprev to iterate through the list of vertices sharing that point.

• To iterate through the vertices of a polygonal face, use primvertexcount to get the number of vertices, then you can use the primitive number and a counter from 0 to ‹primitive count› - 1 to refer to the vertices.

• A vertex number is the 0-based index of a certain vertex of a primitive. A linear vertex number is the 0-based index of a certain primitive across all the geometry. It is just a slightly more convenient way to refer to a vertex with one number instead of two (primitive number and vertex number). You can use vertexindex to get a linear vertex number from a primitive number and a vertex number. Use both vertexprim and vertexprimindex to convert the other way, from a linear vertex number to a primitive number and a vertex number.