Greiner-Hormann

Greiner-Hormann clipping algorithm

The algorithm is a rough implementation of Gunther Greiner a Kai Hormann "Efficient Clipping of Arbitrary Polygons". You can use it in browser or node.

• Does AND, OR, XOR (intersection, union, difference, if you're human)
• Plays nicely with Leaflet, comes with an adaptor for it
• Handles non-convex polygons and multiple clipping areas
• ~3kb compressed, no dependencies

Examples

AND (Intersection)

OR (union)

XOR (diff)

There are 3 bundles in the dist dir:

• greiner-hormann(.min).js - algorithm, requires Array.isArray polyfill, you can find it in libs
• greiner-hormann.leaflet(.min).js - algorithm + adapter for Leaflet.

All minified versions are compiled with Google Closure Compiler in ADVANCED mode.

Usage

npm

$ npm install greiner-hormann

<script src="dist/greiner-hormann.leaflet.min.js"></script>
<script>
...
var intersection = greinerHormann.intersection(source, clip);
var union        = greinerHormann.union(source, clip);
var diff         = greinerHormann.diff(source, clip);

...

if(intersection){
    if(typeof intersection[0][0] === 'number'){ // single linear ring
        intersection = [intersection];
    }
    for(var i = 0, len = intersection.length; i < len; i++){
        L.polygon(intersection[i], {...}).addTo(map);
    }
}
</script>

Results

The output of the binary operation could be one or several linear rings, or null, you have to check.

Code

Although being adapted for use with leaflet, algorithm uses it's own polygon and vertex abstraction, mainly for the better understanding of the algorithm and flexibility. Maybe I'll provide a plain L.PolyUtils. ... implementation for that in the future.

Development

It's an early version, some implications may occur when trying to make operation with polygons that are crossing the date change line, for that we'll have to dissect the polygons and treat the parts separately. Also some adaptation is needed to handle holes(entry/exit points analysis).

Following will re-bundle and re-compile the code in the dist folder. Be careful, Google Closure compiler won't output any errors or warnings with current settings.

$ make

Authors and Contributors

Alexander Milevski @w8r

Thanks to @helderco

License

(The MIT License)

Copyright (c) 2014 Alexander Milevski [email protected]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.