Maps, Infovis, Code
Published
Edited
May 17, 2018
4 forks
Importers
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Cartographic Experiments
/*
Generate points at random locations inside polygon.
polygon: polygon (Array of points [x,y])
numPoints: number of points to generate
Returns an Array of points [x,y].
The returned Array will have a property complete, which is set to false if the
desired number of points could not be generated within `options.numIterations` attempts
*/
function makeDots(polygon, numPoints, options) {
options = Object.assign({
// DEFAULT OPTIONS:
maxIterations: numPoints * 50,
distance: null, // by default: MIN(width, height) / numPoints / 4,
edgeDistance: options.distance
},options);
numPoints = Math.floor(numPoints)
// calculate bounding box
let xMin = Infinity,
yMin = Infinity,
xMax = -Infinity,
yMax = -Infinity
polygon.forEach(p => {
if (p[0]<xMin) xMin = p[0]
if (p[0]>xMax) xMax = p[0]
if (p[1]<yMin) yMin = p[1]
if (p[1]>yMax) yMax = p[1]
});
let width = xMax - xMin
let height = yMax - yMin
// default options depending on bounds
options.distance = options.distance || Math.min(width, height) / numPoints / 4
options.edgeDistance = options.edgeDistance || options.distance
// generate points
let points = [];
outer:
for (let i=0; i<options.maxIterations; i++) {
let p = [xMin + Math.random() * width, yMin + Math.random() * height]
if (d3.polygonContains(polygon, p)) {
// check distance to other points
for (let j=0; j<points.length; j++) {
let dx = p[0]-points[j][0],
dy = p[1]-points[j][1]
if (Math.sqrt(dx*dx+dy*dy) < options.distance) continue outer;
}
// check distance to polygon edge
for (let j=0; j<polygon.length-1; j++) {
if (distPointEdge(p, polygon[j], polygon[j+1]) < options.edgeDistance) continue outer;
}
points.push(p);
if (points.length == numPoints) break;
}
}
points.complete = (points.length >= numPoints)
return points
}
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