130 lines
4.1 KiB
JavaScript
130 lines
4.1 KiB
JavaScript
var point = require('@turf/helpers').point;
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var polygon = require('@turf/helpers').polygon;
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var distance = require('@turf/distance');
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var featurecollection = require('@turf/helpers').featureCollection;
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//Precompute cosines and sines of angles used in hexagon creation
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// for performance gain
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var cosines = [];
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var sines = [];
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for (var i = 0; i < 6; i++) {
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var angle = 2 * Math.PI / 6 * i;
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cosines.push(Math.cos(angle));
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sines.push(Math.sin(angle));
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}
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/**
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* Takes a bounding box and a cell size in degrees and returns a {@link FeatureCollection} of flat-topped
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* hexagons ({@link Polygon} features) aligned in an "odd-q" vertical grid as
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* described in [Hexagonal Grids](http://www.redblobgames.com/grids/hexagons/).
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*
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* @name hexGrid
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* @param {Array<number>} bbox extent in [minX, minY, maxX, maxY] order
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* @param {number} cellSize dimension of cell in specified units
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* @param {string} [units=kilometers] used in calculating cellSize, can be degrees, radians, miles, or kilometers
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* @param {boolean} [triangles=false] whether to return as triangles instead of hexagons
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* @returns {FeatureCollection<Polygon>} a hexagonal grid
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* @example
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* var bbox = [-96,31,-84,40];
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* var cellSize = 50;
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* var units = 'miles';
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*
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* var hexgrid = turf.hexGrid(bbox, cellSize, units);
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*
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* //=hexgrid
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*/
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module.exports = function hexGrid(bbox, cellSize, units, triangles) {
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var xFraction = cellSize / (distance(point([bbox[0], bbox[1]]), point([bbox[2], bbox[1]]), units));
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var cellWidth = xFraction * (bbox[2] - bbox[0]);
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var yFraction = cellSize / (distance(point([bbox[0], bbox[1]]), point([bbox[0], bbox[3]]), units));
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var cellHeight = yFraction * (bbox[3] - bbox[1]);
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var radius = cellWidth / 2;
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var hex_width = radius * 2;
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var hex_height = Math.sqrt(3) / 2 * cellHeight;
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var box_width = bbox[2] - bbox[0];
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var box_height = bbox[3] - bbox[1];
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var x_interval = 3 / 4 * hex_width;
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var y_interval = hex_height;
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var x_span = box_width / (hex_width - radius / 2);
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var x_count = Math.ceil(x_span);
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if (Math.round(x_span) === x_count) {
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x_count++;
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}
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var x_adjust = ((x_count * x_interval - radius / 2) - box_width) / 2 - radius / 2;
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var y_count = Math.ceil(box_height / hex_height);
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var y_adjust = (box_height - y_count * hex_height) / 2;
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var hasOffsetY = y_count * hex_height - box_height > hex_height / 2;
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if (hasOffsetY) {
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y_adjust -= hex_height / 4;
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}
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var fc = featurecollection([]);
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for (var x = 0; x < x_count; x++) {
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for (var y = 0; y <= y_count; y++) {
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var isOdd = x % 2 === 1;
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if (y === 0 && isOdd) {
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continue;
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}
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if (y === 0 && hasOffsetY) {
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continue;
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}
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var center_x = x * x_interval + bbox[0] - x_adjust;
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var center_y = y * y_interval + bbox[1] + y_adjust;
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if (isOdd) {
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center_y -= hex_height / 2;
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}
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if (triangles) {
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fc.features.push.apply(fc.features, hexTriangles([center_x, center_y], cellWidth / 2, cellHeight / 2));
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} else {
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fc.features.push(hexagon([center_x, center_y], cellWidth / 2, cellHeight / 2));
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}
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}
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}
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return fc;
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};
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//Center should be [x, y]
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function hexagon(center, rx, ry) {
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var vertices = [];
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for (var i = 0; i < 6; i++) {
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var x = center[0] + rx * cosines[i];
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var y = center[1] + ry * sines[i];
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vertices.push([x, y]);
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}
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//first and last vertex must be the same
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vertices.push(vertices[0]);
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return polygon([vertices]);
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}
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//Center should be [x, y]
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function hexTriangles(center, rx, ry) {
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var triangles = [];
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for (var i = 0; i < 6; i++) {
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var vertices = [];
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vertices.push(center);
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vertices.push([
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center[0] + rx * cosines[i],
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center[1] + ry * sines[i]
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]);
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vertices.push([
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center[0] + rx * cosines[(i + 1) % 6],
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center[1] + ry * sines[(i + 1) % 6]
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]);
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vertices.push(center);
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triangles.push(polygon([vertices]));
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}
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return triangles;
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}
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