//计算三角形面积 function triangleArea(p0, p1, p2) { let v0 = Cesium.Cartesian3.subtract(p0, p1, new Cesium.Cartesian3()) let v1 = Cesium.Cartesian3.subtract(p2, p1, new Cesium.Cartesian3()) let cross = Cesium.Cartesian3.cross(v0, v1,v0); return Cesium.Cartesian3.magnitude(cross) * 0.5 } //计算多边形面积 function area(positions) { let result = 0 if (!Array.isArray(positions)) { console.log('不是数组'); return result } if (!(positions[0] instanceof Cesium.Cartesian3)) { console.log('不是Cartesian3'); //转换为Cartesian3数组 positions = Transform.transformWGS84ArrayToCartesianArray(positions); } //创建一个geometry let geometry = Cesium.CoplanarPolygonGeometry.createGeometry( Cesium.CoplanarPolygonGeometry.fromPositions({ positions: positions, vertexFormat: Cesium.VertexFormat.POSITION_ONLY }) ) if (!geometry) { console.log('不是geometry'); return result } //顶点坐标数组p; let flatPositions = geometry.attributes.position.values console.log(flatPositions); //确定geometry的基本体的索引,也就是组成其的三角形的索引,每三个为一组,组成一个三角形 let indices = geometry.indices console.log(indices); //计算三角形面积,最后加在一起 for (let i = 0; i < indices.length; i += 3) { let p0 = Cesium.Cartesian3.unpack( flatPositions, indices[i] * 3, new Cesium.Cartesian3() ) console.log(p0); let p1 = Cesium.Cartesian3.unpack( flatPositions, indices[i + 1] * 3, new Cesium.Cartesian3() ) console.log(p1); let p2 = Cesium.Cartesian3.unpack( flatPositions, indices[i + 2] * 3, new Cesium.Cartesian3() ) console.log(p2); result += triangleArea(p0, p1, p2) } return result } //一个正方形的四个端点 var p0 = new Cesium.Cartesian3(0,0,0); var p1 = new Cesium.Cartesian3(1,0,0); var p2 = new Cesium.Cartesian3(1,1,0); var p3 = new Cesium.Cartesian3(0,1,0); var input = [p0,p1,p2,p3]; var output = area(input); console.log(output);
顶点坐标数组flatPositions:
确定geometry的基本体的索引,也就是组成其的三角形的索引,每三个为一组,组成一个三角形indices:
也就是顶点2、3、0组成一个三角形,0,1,2组成一个三角形
至于代码中为了要乘3,是为了保证每次取的数组是连续的,比如2、3、0乘3是6、9、0,从6开始取三个6,7,8,从9开始取三个9,10,11,从0开始取三个0,1,2,这样取到的三个点才是正确的三角形
用到的一些方法:
Cesium.CoplanarPolygonGeometry.createGeometry 创建geometry Cesium.Cartesian3.unpack 从数组中生成Cartesian3 Cesium.Cartesian3.subtract 相减,用于生成向量 Cesium.Cartesian3.cross 求叉积 Cesium.Cartesian3.magnitude 求向量的长度 Array.isArray 判断是否是数组
标签:十一,多边形,Cartesian3,geometry,let,new,Cesium,console From: https://www.cnblogs.com/LJXXXX/p/17067917.html