R: Extract a list of triangles from a triangulation object

triangles {interp} | R Documentation

## Extract a list of triangles from a triangulation object

### Description

This function extracts a list of triangles from an triangulation object created by `tri.mesh`.

### Usage

    triangles(tri.obj)

### Arguments

`tri.obj` | object of class `triSht`

### Details

The vertices in the returned matrix (let's denote it with `retval`) are ordered counterclockwise. The columns `tr`x and `arc`x, x=1,2,3 index the triangle and arc, respectively, which are opposite (not shared by) node `node`x, with `tri`x=0 if `arc`x indexes a boundary arc. Vertex indexes range from 1 to n, the number of nodes, triangle indexes from 0 to nt, and arc indexes from 1 to na = nt+n-1.

### Value

A matrix with columns `node1`, `node2`, `node3`, representing the vertex nodal indexes, `tr1`, `tr2`, `tr3`, representing neighboring triangle indexes and `arc1`, `arc2`, `arc3` reresenting arc indexes.

Each row represents one triangle.

### Author(s)

Albrecht Gebhardt <albrecht.gebhardt@aau.at>, Roger Bivand <roger.bivand@nhh.no>

### See Also

`triSht`, `print.triSht`, `plot.triSht`, `summary.triSht`, `triangles`

### Examples

    # use the smallest Franke data set
    data(franke)
    fr3.tr<-tri.mesh(franke$ds3$x, franke$ds3$y)
    triangles(fr3.tr)

[Package interp version 1.0-33 Index]