Definition
In a CAD model, topology describes how geometric elements, faces, edges and vertices, are connected: which faces share an edge, which edges meet at a vertex. It is distinct from geometry, which describes exact shape, size and position. Two parts can have identical topology but different geometry (a block with a hole, at two different hole sizes), or the same nominal shape with different topology (one continuous fillet versus a fillet split into two faces).
Why topology matters for automated recognition
Feature recognition and manufacturability checks often work at the topology level first, identifying patterns of connected faces that correspond to a hole, pocket or slot, before reasoning about exact dimensions.
Where topology lives
Not shown directly; it is an internal property of the 3D CAD model (typically a B-rep) rather than something annotated on a drawing.
Common mistakes
Confusing topology with geometry: a change in topology (splitting one face into two, merging two holes into a slot) can be a much bigger deal for downstream software than a change in a single dimension.
Feature recognition and manufacturability checks often work at the topology level first, identifying patterns of connected faces that correspond to a hole, pocket or slot, before reasoning about exact dimensions.
See how Blake reviews a partFrequently asked questions
Is topology the same as geometry?
No, geometry is exact shape, size and position; topology is how the elements connect, independent of exact dimensions.
Why does topology matter for feature recognition?
Because recognising a manufacturing feature (a hole, pocket, slot) often starts by matching a topological pattern, before checking exact dimensions.
Can two parts have the same topology but look different?
Yes; a block with a small hole and a block with a large hole can have identical topology, differing only in geometry.