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Split a Mesh into Connected Triangle Groups

Source: R/splitTrianglesInd.R
splitTrianglesInd.Rd

Groups the triangles of a 3D mesh into independent subsets according to connectivity, i.e., if they share an edge (two vertices). Each connected component is returned as a group of indices corresponding to triangles belonging to the same piece or mesh fragment.

Usage

splitTrianglesInd(mesh)

Arguments

mesh

A mesh3d object containing the mesh to analyze. It must include the it matrix, where each column represents a triangle defined by the indices of its vertices.

Value

A list where each element contains the indices of triangles forming a connected component of the mesh. If there are no connections between triangles, each list element corresponds to a single triangle.

Details

This procedure is useful when the mesh contains multiple disconnected parts (e.g., reinforcements, panels, or separate fragments) and they need to be handled separately for geometric analysis, visualization, or data cleaning.

The algorithm follows these steps:

  1. Checks that the mesh contains the it matrix with triangles.

  2. For each vertex, records the triangles in which it appears.

  3. Determines pairs of triangles that share an edge (two common vertices).

  4. Builds an undirected graph with triangles as nodes and shared-edge connections as edges.

  5. Identifies the connected components of the graph using igraph::components().

See also

igraph::graph(), igraph::components()

Examples

require(igraph)
#> Loading required package: igraph
#> 
#> Attaching package: 'igraph'
#> The following objects are masked from 'package:stats':
#> 
#>     decompose, spectrum
#> The following object is masked from 'package:base':
#> 
#>     union

# Create a mesh3d object with two disconnected triangles
vb <- t(rbind(
  c(0, 0, 0),
  c(1, 0, 0),
  c(0, 1, 0),
  c(2, 0, 0),
  c(3, 0, 0),
  c(2, 1, 0)
))
it <- t(rbind(
  c(1, 2, 3),
  c(4, 5, 6)
))
mesh <- rgl::tmesh3d(vertices = vb, indices = it)

# Split the mesh into connected triangle groups
groups <- splitTrianglesInd(mesh)
str(groups)
#> List of 2
#>  $ : int 1
#>  $ : int 2