deldir (version 2.0-4)

triMat: Produce matrix of triangle vertex indices.

Description

Lists the indices of the vertices of each Delaunay triangle in the triangulation of a planar point set. The indices are listed (in increasing numeric order) as the rows of an \(n \times 3\) matrix where \(n\) is the number of Delaunay triangles in the triangulation.

Usage

triMat(object)

Value

An \(n \times 3\) matrix where \(n\) is the number of Delaunay triangles in the triangulation specified by object. The \(i^{th}\) row consists of the indices (in the original list of points being triangulated) of vertices of the \(i^{th}\)

Delaunay triangle. The indices are listed in increasing numeric order in each row.

Arguments

object

An object of class deldir (as produced by the function deldir()) specifying the Delaunay triangulation and Dirichlet (Voronoi) tessellation of a planar point set.

Author

Rolf Turner

Details

This function was suggested by Robin Hankin of the School of Mathematical and Computing Sciences at Auckland University of Technology.

See Also

deldir() triang.list() plot.triang.list()

Examples

# These are the data used by Jay Call to illustrate the bug
# that appeared in a previous incarnation of triMat.
xy <- data.frame(
          x = c(0.048,0.412,0.174,0.472,0.607,0.565,0.005,0.237,0.810,0.023),
          y = c(0.512,0.928,0.955,0.739,0.946,0.134,0.468,0.965,0.631,0.782)
      )
dxy <- deldir(xy)
M   <- triMat(dxy)
plot(dxy,wlines="triang",num=TRUE,axes=FALSE,cmpnt_col=c(1,1,1,1,2,1))
# The triangle with vertices {4,5,8} was listed in the output of
# the previous (buggy) version of triMat().  It is NOT a Delaunay
# triangle and hence should NOT be listed.