## DESCRIPTION

This module is for miscellaneous PP-defined utility routines for the PDL::Graphics::TriD module. Currently, there are## FUNCTIONS

## combcoords

Signature: (x(); y(); z(); float [o]coords(tri=3);)

Combine three coordinates into a single piddle.

Combine x, y and z to a single piddle the first dimension of which is 3. This routine does dataflow automatically.

combcoords does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

## repulse

Signature: (coords(nc,np); [o]vecs(nc,np); int [t]links(np);; double boxsize; int dmult; double a; double b; double c; double d; )

Repulsive potential for molecule-like constructs.

`"repulse"` uses a hash table of cubes to quickly calculate
a repulsive force that vanishes at infinity for many
objects. For use by the module PDL::Graphics::TriD::MathGraph.
For definition of the potential, see the actual function.

repulse does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

## attract

Signature: (coords(nc,np); int from(nl); int to(nl); strength(nl); [o]vecs(nc,np);; double m; double ms; )

Attractive potential for molecule-like constructs.

`"attract"` is used to calculate
an attractive force for many
objects, of which some attract each other (in a way
like molecular bonds).
For use by the module PDL::Graphics::TriD::MathGraph.
For definition of the potential, see the actual function.

attract does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

## vrmlcoordsvert

Signature: (vertices(n=3); char* space; char* fd)

info not available

vrmlcoordsvert does not process bad values. It will set the bad-value flag of all output piddles if the flag is set for any of the input piddles.

## contour_segments

This is the interface for the pp routine contour_segments_internal - it takes 3 piddles as input
`$c` is a contour value (or a list of contour values)

`$data` is an [m,n] array of values at each point

`$points` is a list of [3,m,n] points, it should be a grid
monotonically increasing with m and n.

contour_segments returns a reference to a Perl array of
line segments associated with each value of `$c`. It does not (yet) handle
missing data values.

- Algorthym
- The data array represents samples of some field observed on the surface described by points. For each contour value we look for intersections on the line segments joining points of the data. When an intersection is found we look to the adjoining line segments for the other end(s) of the line segment(s). So suppose we find an intersection on an x-segment. We first look down to the left y-segment, then to the right y-segment and finally across to the next x-segment. Once we find one in a box (two on a point) we can quit because there can only be one. After we are done with a given x-segment, we look to the leftover possibilities for the adjoining y-segment. Thus the contours are built as a collection of line segments rather than a set of closed polygons.

## AUTHOR

Copyright (C) 2000 James P. Edwards Copyright (C) 1997 Tuomas J. Lukka. All rights reserved. There is no warranty. You are allowed to redistribute this software / documentation under certain conditions. For details, see the file COPYING in the PDL distribution. If this file is separated from the PDL distribution, the copyright notice should be included in the file.