73 lines
1.7 KiB
JavaScript
73 lines
1.7 KiB
JavaScript
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/**
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* Created by bingqixuan on 2018/5/3.
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*/
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const {Cartesian3, Cartographic} = require('cesium');
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/**
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* 计算Polygon的质心
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* @param positions [Array]
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* @returns {Cartographic}
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*/
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const computeCentroidOfPolygon = function (positions) {
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let x = [];
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let y = [];
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for (let i = 0; i < positions.length; i++) {
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let cartographic = Cartographic.fromCartesian(positions[i]);
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x.push(cartographic.longitude);
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y.push(cartographic.latitude);
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}
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let x0 = 0.0, y0 = 0.0, x1 = 0.0, y1 = 0.0;
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let signedArea = 0.0;
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let a = 0.0;
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let centroidx = 0.0, centroidy = 0.0;
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for (i = 0; i < positions.length; i++) {
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x0 = x[i];
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y0 = y[i];
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if (i === positions.length - 1) {
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x1 = x[0];
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y1 = y[0];
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} else {
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x1 = x[i + 1];
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y1 = y[i + 1];
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}
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a = x0 * y1 - x1 * y0;
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signedArea += a;
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centroidx += (x0 + x1) * a;
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centroidy += (y0 + y1) * a;
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}
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signedArea *= 0.5;
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centroidx /= (6.0 * signedArea);
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centroidy /= (6.0 * signedArea);
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return new Cartographic(centroidx, centroidy);
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};
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/**
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* 计算三角形面积
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* @param pos1 {Cartesian3} 第一点
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* @param pos2 {Cartesian3} 第二点
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* @param pos3 {Cartesian3} 第三点
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* @returns {number}
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*/
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const computeAreaOfTriangle = function (pos1, pos2, pos3) {
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let a = Cartesian3.distance(pos1, pos2);
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let b = Cartesian3.distance(pos2, pos3);
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let c = Cartesian3.distance(pos3, pos1);
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let S = (a + b + c) / 2;
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return Math.sqrt(S * (S - a) * (S - b) * (S - c));
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};
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module.exports = {
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computeAreaOfTriangle: computeAreaOfTriangle,
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computeCentroidOfPolygon: computeCentroidOfPolygon
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};
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