Weld the vertices of a mesh and remove degenerate faces.

Meshes returned by the marching cubes implementations are usually not clean: Rvcg::vcgIsosurface() returns duplicated vertices along with a large number of degenerate (zero area) faces which overlap the real faces, and misc3d::contour3d() returns completely unwelded meshes, i.e., one vertex per triangle corner. Both waste memory and render badly when lighting is enabled: the degenerate faces get invalid normals and fight for the same depth values as the real faces, which makes the surface look patched, grooved and partly black instead of smoothly shaded. This function welds vertices which are at (numerically) identical positions, removes the faces which use the same vertex more than once, and recomputes the normals.

Usage

mesh.weld(mesh, drop_degenerate = TRUE, add_normals = TRUE, tolerance = 1e-06)

Arguments

mesh

a mesh3d instance, e.g., as returned by Rvcg::vcgIsosurface(), misc3d::contour3d() or shell.extract.mesh.

drop_degenerate

logical, whether to remove the degenerate faces, i.e., the faces which have at least two coincident corners and thus zero area. Defaults to TRUE.

add_normals

logical, whether to compute per-vertex normals for the result. Defaults to TRUE.

tolerance

numerical scalar, the distance (in the units of the mesh coordinates, typically mm) below which two vertices are considered identical. Defaults to 1e-6.

Value

a mesh3d instance with welded vertices, without degenerate faces, and with normals if requested. Vertices which are not used by any face are dropped, so per-vertex data like colors has to be assigned after welding (see the note).

Note

Welding changes the vertex array, so per-vertex data which is not part of the mesh (e.g., a color vector) cannot be preserved. Assign such data to the welded mesh, which is what the visualization functions do internally.