fm_mesh_components: Compute connected mesh subsets

In fmesher: Triangle Meshes and Related Geometry Tools

Compute connected mesh subsets

Description

Compute subsets of vertices and triangles/tetrahedrons in an fm_mesh_2d or fm_mesh_3d object that are connected by edges/triangles.

Usage

fm_mesh_components(mesh)

## S3 method for class 'fm_mesh_2d'
fm_mesh_components(mesh)

## S3 method for class 'fm_mesh_3d'
fm_mesh_components(mesh)

Arguments

mesh	An fm_mesh_2d or fm_mesh_3d object

Value

A list with elements vertex and triangle/tetra, vectors of integer labels for which connected component they belong, and info, a data.frame with columns

component	Connected component integer label.
nV	The number of vertices in the component.
nT	The number of triangles/tetrahedrons in the component.
area/volume	The surface area or volume associated with the component. Component labels are not comparable across different meshes, but some ordering stability is guaranteed by initiating each component from the lowest numbered triangle whenever a new component is initiated.

Author(s)

Finn Lindgren [e-mail]

See Also

fm_mesh_2d(), fm_rcdt_2d(), fm_mesh_3d()

Examples

# Construct two simple meshes:
loc <- matrix(c(0, 1, 0, 1), 2, 2)
mesh1 <- fm_mesh_2d(loc = loc, max.edge = 0.1)
bnd <- fm_nonconvex_hull(loc, 0.3)
mesh2 <- fm_mesh_2d(boundary = bnd, max.edge = 0.1)

# Compute connectivity information:
conn1 <- fm_mesh_components(mesh1)
conn2 <- fm_mesh_components(mesh2)
# One component, simply connected mesh
conn1$info
# Two disconnected components
conn2$info

# Extract the subset mesh for each component:
# (Note: some information is lost, such as fixed segments,
# and boundary edge labels.)
mesh3_1 <- fm_rcdt_2d_inla(
  loc = mesh2$loc,
  tv = mesh2$graph$tv[conn2$triangle == 1, , drop = FALSE],
  delaunay = FALSE
)
mesh3_2 <- fm_rcdt_2d_inla(
  loc = mesh2$loc,
  tv = mesh2$graph$tv[conn2$triangle == 2, , drop = FALSE],
  delaunay = FALSE
)

if (require("ggplot2")) {
  ggplot() +
    geom_fm(data = mesh3_1, fill = "red", alpha = 0.5) +
    geom_fm(data = mesh3_2, fill = "blue", alpha = 0.5)
}

(m <- fm_mesh_3d(
  matrix(c(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0), 4, 3, byrow = TRUE),
  matrix(c(1, 2, 3, 4), 1, 4, byrow = TRUE)
))
# Compute connectivity information:
(conn <- fm_mesh_components(m))

fmesher documentation built on June 12, 2025, 5:09 p.m.