# tri: A triangulation object In tripack: Triangulation of Irregularly Spaced Data

## Description

R object that represents the triangulation of a set of 2D points, generated by `tri.mesh` or `add.constraint`.

## Arguments

 `n` Number of nodes `x` x coordinates of the triangulation nodes `y` y coordinates of the triangulation nodes `tlist` Set of nodal indexes which, along with `tlptr`, `tlend`, and `tlnew`, define the triangulation as a set of n adjacency lists – counterclockwise-ordered sequences of neighboring nodes such that the first and last neighbors of a boundary node are boundary nodes (the first neighbor of an interior node is arbitrary). In order to distinguish between interior and boundary nodes, the last neighbor of each boundary node is represented by the negative of its index. `tlptr` Set of pointers in one-to-one correspondence with the elements of `tlist`. `tlist[tlptr[i]]` indexes the node which follows `tlist[i]` in cyclical counterclockwise order (the first neighbor follows the last neighbor). `tlend` Set of pointers to adjacency lists. `tlend[k]` points to the last neighbor of node k for k = 1,...,n. Thus, `tlist[tlend[k]]`<0 if and only if k is a boundary node. `tlnew` Pointer to the first empty location in `tlist` and `tlptr` (list length plus one). `nc` number of constraints `lc` starting indices of constraints in `x` and `y` `call` call, which generated this object

## Note

The elements `tlist`, `tlptr`, `tlend` and `tlnew` are mainly intended for internal use in the appropriate Fortran routines.

A. Gebhardt

## References

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

`tri.mesh`, `print.tri`, `plot.tri`, `summary.tri`