pathtrim-pslg
v1.1.0
Published
Trims a set of lines based on a planar graph
Downloads
4
Maintainers
Readme
pathtrim-pslg
This module trims the edges in a planar straight line graph (pslg) based on another planar straight line graph.
This code is a modified version of Mikola Lysenko's overlay-pslg code. It is correct to the best of my knowledge, but I suspect there are simpler correct algorithms in the literature.
Example
Here is a simple example showing how to use this module to compute the intersection of two PSLGs:
//Load the module
var pathtrim = require('pathtrim-pslg')
//Red PSLG - Define a triangle
var pathPoints = [
[0.5, 0.25],
[0.25, 0.5],
[0.75, 0.75]
]
var pathEdges = [ [0,1], [1,2], [2,0] ]
//Blue PSLG - Define a square
var polyPoints = [
[0.25, 0.25],
[0.25, 0.6],
[0.6, 0.6],
[0.6, 0.25]
]
var polyEdges = [ [0,1], [1,2], [2,3], [3,0] ]
//Construct intersection
console.log(pathtrim(pathPoints, pathEdges, polyPoints, polyEdges, false))
Output
The result of this module is the following JSON:
{ points:
[ [ 0.75, 0.75 ],
[ 0.44999999999999996, 0.6 ],
[ 0.6, 0.44999999999999996 ] ],
edges: [ [ 0, 1 ], [ 0, 2 ] ] }
We can visualize this result as follows:
Install
To install this module, you can use npm. The command is as follows:
npm i pathtrim-pslg
It works in any reasonable CommonJS environment like node.js. If you want to use it in a browser, you should use browserify.
API
require('pathtrim-pslg')(linePoints, lineEdges, bluePoints, blueEdges[, intersectMode])
Computes a Boolean operation between two planar straight line graphs.
linePoints, lineEdges
are the points and edges of the paths that will be cut upbluePoints, blueEdges
are the points and edges of the polygonsintersectMode
specifies if we're in intersect mode (true
) or subtract mode (false
)
Returns An object encoding a planar straight line graph with the remaining line segments
points
are the points of the resultedges
are the edges we have kept, indexing into thepoints
array.
Note The interiors of the polygon are computed using cdt2d
. It counts the parity of the path with the fewest number of boundary crossings for each point. Even parity points are in the exterior, odd parity in the interior.
License
(c) 2017 Joseph Gentle, Mikola Lysenko. MIT License