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Added algorithm customizations

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This commit is contained in:
Fabian Wunsch 2022-04-12 17:29:40 +02:00
parent 53a92f29c3
commit 1e52cdaa95
2 changed files with 28 additions and 16 deletions
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2
web/_js/draw.js
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@ -229,7 +229,7 @@ window.initDraw = function(){
function calculateCenter(path){
let result = polylabel(path)
let result = polylabel(path, 0.5, true)
return [Math.floor(result[0]) + 0.5, Math.floor(result[1]) + 0.5]
}

40
web/_js/polylabel.js
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@ -5,7 +5,7 @@ import TinyQueue from 'https://cdn.jsdelivr.net/npm/tinyqueue@2.0.3/index.min.js
if (TinyQueue.default) TinyQueue = TinyQueue.default; // temporary webpack fix
export default function polylabel(polygon, precision, debug) {
precision = precision || 1.0;
precision = precision || 0.5;
// find the bounding box of the outer ring
var minX, minY, maxX, maxY;
@ -31,28 +31,34 @@ export default function polylabel(polygon, precision, debug) {
// a priority queue of cells in order of their "potential" (max distance to polygon)
var cellQueue = new TinyQueue(undefined, compareMax);
let centroid = getCentroid(polygon);
// cover polygon with initial cells
for (var x = minX; x < maxX; x += cellSize) {
for (var y = minY; y < maxY; y += cellSize) {
cellQueue.push(new Cell(x + h, y + h, h, polygon));
cellQueue.push(new Cell(x + h, y + h, h, polygon, centroid));
}
}
// take centroid as the first best guess
var bestCell = getCentroidCell(polygon);
var bestCell = getCentroidCell(centroid, polygon);
// second guess: bounding box centroid
var bboxCell = new Cell(minX + width / 2, minY + height / 2, 0, polygon);
var bboxCell = new Cell(minX + width / 2, minY + height / 2, 0, polygon, centroid);
if (bboxCell.d > bestCell.d) bestCell = bboxCell;
var numProbes = cellQueue.length;
let threshold = Math.log10(cellSize) / 3.0
while (cellQueue.length) {
// pick the most promising cell from the queue
var cell = cellQueue.pop();
// update the best cell if we found a better one
if (cell.d > bestCell.d) {
if (cell.d > bestCell.d || (
cell.centerDist < bestCell.centerDist &&
cell.d > bestCell.d - threshold
)) {
bestCell = cell;
if (debug) console.log('found best %f after %d probes', Math.round(1e4 * cell.d) / 1e4, numProbes);
}
@ -62,10 +68,10 @@ export default function polylabel(polygon, precision, debug) {
// split the cell into four cells
h = cell.h / 2;
cellQueue.push(new Cell(cell.x - h, cell.y - h, h, polygon));
cellQueue.push(new Cell(cell.x + h, cell.y - h, h, polygon));
cellQueue.push(new Cell(cell.x - h, cell.y + h, h, polygon));
cellQueue.push(new Cell(cell.x + h, cell.y + h, h, polygon));
cellQueue.push(new Cell(cell.x - h, cell.y - h, h, polygon, centroid));
cellQueue.push(new Cell(cell.x + h, cell.y - h, h, polygon, centroid));
cellQueue.push(new Cell(cell.x - h, cell.y + h, h, polygon, centroid));
cellQueue.push(new Cell(cell.x + h, cell.y + h, h, polygon, centroid));
numProbes += 4;
}
@ -80,15 +86,17 @@ export default function polylabel(polygon, precision, debug) {
}
function compareMax(a, b) {
return b.max - a.max;
return b.weight - a.weight;
}
function Cell(x, y, h, polygon) {
function Cell(x, y, h, polygon, centroid) {
this.x = x; // cell center x
this.y = y; // cell center y
this.h = h; // half the cell size
this.d = pointToPolygonDist(x, y, polygon); // distance from cell center to polygon
this.centerDist = (centroid[0] - x) ** 2 + (centroid[1] - y) ** 2
this.max = this.d + this.h * Math.SQRT2; // max distance to polygon within a cell
this.weight = -this.centerDist - this.max
}
// signed distance from point to polygon outline (negative if point is outside)
@ -110,7 +118,7 @@ function pointToPolygonDist(x, y, polygon) {
}
// get polygon centroid
function getCentroidCell(polygon) {
function getCentroid(polygon) {
var area = 0;
var x = 0;
var y = 0;
@ -123,8 +131,12 @@ function getCentroidCell(polygon) {
y += (a[1] + b[1]) * f;
area += f * 3;
}
if (area === 0) return new Cell(polygon[0][0], polygon[0][1], 0, polygon);
return new Cell(x / area, y / area, 0, polygon);
if (area === 0) return [polygon[0][0], polygon[0][1]];
return [x / area, y / area];
}
function getCentroidCell(centroid, polygon) {
return new Cell(centroid[0], centroid[1], 0, polygon, centroid);
}
// get squared distance from a point to a segment