Does EdgeSplit modify geometry?

Question

I'm making robot models exported from SolidWorks look better by smoothing the shading of the faces, here is my work-flow:

• Import mesh
• Remove double vertices
• Smooth faces
• Apply EdgeSplit
• Export final model

This works great but I am not sure of one thing, from what I understand the EdgeSplit modifier only modifies the vertices normals on specific regions of the mesh (given the split angle).

When applying the work-flow above on some meshes (example), the poly count changes and I don't understand why:

• Original file: 230 vertices
• Removed doubles: 226 vertices
• Smooth faces: 226 vertices
• After EdgeSplit: 421 vertices

Why is the EdgeSplit affecting the poly-count in some cases and other not?

Answer 1

Yes, the Edge Split modifier does modify the geometry.

Edge Split works by actually splitting edges, i.e. making an edge two separate (overlapping) edges. This is why your vertex count goes up after applying edge split, each vertex which is on an edge that got split is turned into two vertices.

Note how the vertex became three separate vertices after Edge Split.

Answer 2

I would have added a comment if I had the reputation. As PGmath answered your question: Edge Split splits the mesh.

But here' more I think you'll find helpful: I have a similar need, exporting from a similar program. (Inventor)

Edgesplit is destructive and not very flexible. The newer bmesh abilities made it mostly obsolete.

Here's how I do it:

• Import the mesh (I have to use STL.)
• Spacebar, "Shade smooth" command.
• In the Object data menu, click "Auto Smooth" and lower the angle.
  I often use 30. just make sure it does not sharpen more than you need. (You can fix the ones that don't get sharpened later.)
• Now you have the effect of Edge Split but without changing the mesh. Perhaps you can stop here. But if there still some that need to be hard edged:
  • Go into editmode.
  • With the edge select mode, (next to "global" at the bottom of the pane.) Select the edges you want to be sharp.
  • "Mark sharp" from the spacebar menu or from the left menu: Shading tab, Edge sharp.

Edit: But you did say you export it later, depending on the exporter and your needs, it may not keep those edges hard. You can still export the split mesh and manually split more if needed.) ...and you can undo split mesh with "remove doubles".