fm_components: Compute connected mesh subsets

In finnlindgren/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, and split fm_segm objects into connected components.

Usage

fm_components(x, ...)

fm_mesh_components(...)

## S3 method for class 'fm_mesh_2d'
fm_components(x, ...)

## S3 method for class 'fm_mesh_3d'
fm_components(x, ...)

## S3 method for class 'fm_segm'
fm_components(x, ...)

## S3 method for class 'fm_segm_list'
fm_components(x, ...)

Arguments

x	An object to extract components from
...	Additional arguments passed to methods

Value

For fm_mesh_2d and fm_mesh_3d, returns 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.

For fm_segm, returns a list of segments, each with component either a single closed loop of segments, or an open segment chain.

Functions

• fm_mesh_components(): Backwards compatibility for version ⁠0.4.0⁠

Author(s)

Finn Lindgren [e-mail]

See Also

fm_mesh_2d(), fm_rcdt_2d(), fm_mesh_3d(), fm_segm()

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_components(mesh1)
conn2 <- fm_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_components(m))

(segm <- c(
  fm_segm(
    matrix(c(0, 0, 1, 0, 1, 1, 0, 1), 4, 2, byrow = TRUE),
    matrix(c(1, 2, 2, 3, 3, 4, 4, 1), 4, 2, byrow = TRUE)
  ),
  fm_segm(
    matrix(c(0, 0, 1, 0, 1, 1, 0, 1), 4, 2, byrow = TRUE),
    matrix(c(3, 4, 1, 2, 2, 3), 3, 2, byrow = TRUE),
    is.bnd = FALSE
  )
))
# Compute connectivity information:
(conn <- lapply(segm, fm_components))
(conn2 <- fm_components(segm))

finnlindgren/fmesher documentation built on July 17, 2025, 1:04 a.m.