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computational-geometrymeshmeshlab

What are the "Faux Edges" on Meshlab?

I have found the concept of Faux Edges in several Meshlab filter descriptions. For example, in the Stratified Triangle Sampling filter, where the description of one of the options is:

Sample NonFaux Edges: Only the non-faux edges of the mesh are uniformly sampled.

enter image description here

What are the Faux (and NonFaux) Edges for meshlab?

Solution

  • Faux (from French, fake) Edges are artificial hidden edges that decompose a polygonal face into triangles. They are automatically inserted by VCGLib when reading a non-triangular mesh to be stored as an internal triangle mesh and to be able to apply many algorithms that are only defined for triangle meshes.

    By definition, a pure-triangular mesh has no faux edges.

    For example, when the well-know Blender Suzanne Monkey model (formed by quad and triangle faces)

    Original Suzanne Monkey

    is loaded into meshlab as a quad mesh, but one faux edge per quad is added under the hood to store it as a triangle mesh. In the image below "Real" or "Nonfaux" edges are rendered in black, while Faux edges are rendered in red.

    Faux Edges in Suzanne

    Unless explicitly indicated, any algorithm that operates on edges (for example, Select crease edges) will only operate on "real edges" and not on faux edges, but many other algorithms (for example, Laplacian Smooth) will operate use faux edges to compute the smooth filters as if the mesh is formed only with triangles.

    Internally, the edges have one VCG flag to determine if they are faux or not, but normally this is not exposed to MeshLab users.

    Upon saving a mesh with faux edges, those will not be saved into the file. So internal triangles of the model that share a faux edge will be joined into a polygonal face.