# triangles

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##### Extract a list of triangle from a triangulation object

This function extracts a triangulation data structure from an triangulation object created by tri.mesh.

The vertices in the returned matrix (let's denote it with retval) are ordered counterclockwise with the first vertex taken to be the one with smallest index. Thus, retval[i,"node2"] and retval[i,"node3"] are larger than retval[i,"node3"] and index adjacent neighbors of node retval[i,"node1"]. The columns trx and arcx, x=1,2,3 index the triangle and arc, respectively, which are opposite (not shared by) node nodex, with trix= 0 if arcx indexes a boundary arc. Vertex indexes range from 1 to N, triangle indexes from 0 to NT, and, if included, arc indexes from 1 to NA = NT+N-1. The triangles are ordered on first (smallest) vertex indexes, except that the sets of constraint triangles (triangles contained in the closure of a constraint region) follow the non-constraint triangles.

##### Usage
triangles(tri.obj)
##### Arguments
tri.obj
object of class "tri"
##### 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.

##### References

R. J. Renka (1996). Algorithm 751: TRIPACK: a constrained two-dimensional {Delaunay} triangulation package. ACM Transactions on Mathematical Software. 22, 1-8.

tri, print.tri, plot.tri, summary.tri, triangles

• triangles
##### Examples
# we will use the test data from library(akima):
library(akima)
data(akima)
akima.tr<-tri.mesh(akima$x,akima$y)
triangles(akima.tr)
Documentation reproduced from package tripack, version 1.0-1, License: R functions: GPL, Fortran code: available at netlib

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