Cesium通視分析

tip:利用兩點(diǎn)間的插值計(jì)算，點(diǎn)A到點(diǎn)B之間，直線距離的高度是否大于地形高度為依據(jù)判斷是否通視。

• 1、3Dtiles 的通視

const startPoint = car3ToLatLon(points[0]); const endPoint = car3ToLatLon(points[1]); // const h_asc = (startPoint.height >= endPoint.height) ? false : true; //兩個(gè)點(diǎn) 哪個(gè)點(diǎn)高 const pointSum = this.pointsNum let cartesians = new Array(pointSum), offset; for (let i = 0; i < pointSum; ++i) {offset = i / (pointSum - 1)cartesians[i] = Cesium.Cartesian3.lerp(points[0], points[1], offset, new Cesium.Cartesian3()) } const cartesians_clone = cartesians.map(d => d.clone()) //啟動(dòng)異步 Scene＃clampToHeight查詢3Dtitle下的位置信息高度等。 this.viewer.scene.clampToHeightMostDetailed(cartesians).then((clampedCartesians: Cesium.Cartesian3[])=> { // 可視終點(diǎn)let line_s_index = 0, position_updated:any,p_update_degree, p_degree, heightArr = [], entityHeightArr = []const length = clampedCartesians.length-1for (let i = 1; i < length; i++) {const position_updated = clampedCartesians[i];p_update_degree = car3ToLatLon(position_updated)p_degree = car3ToLatLon(cartesians_clone[i])heightArr.push(p_degree.height)entityHeightArr.push(p_update_degree.height)}this.heightArr = heightArrthis.entityHeightArr = entityHeightArrfor (let i = 1; i < length; i++) {position_updated = clampedCartesians[i];// 會(huì)有找不到的情況if(!line_s_index && position_updated) {p_update_degree = car3ToLatLon(position_updated)p_degree = car3ToLatLon(cartesians_clone[i])if (p_update_degree.height > p_degree.height) {line_s_index = i;break;}}}let line_e_index = line_s_index;if (callback) {this.isTrue = !!line_s_indexconst labelText = `起點(diǎn)坐標(biāo)：${startPoint.lon.toFixed(2)} | ${startPoint.lat.toFixed(2)}| ${startPoint.height.toFixed()}\n終點(diǎn)坐標(biāo)：${endPoint.lon.toFixed(2)} | ${endPoint.lat.toFixed(2)}| ${endPoint.height.toFixed()}\n通視結(jié)果: ${line_s_index > 0 ? '否' : '是'}`callback({'line_s_end': cartesians_clone[line_s_index],'line_e_start': cartesians_clone[line_e_index],'labelResult': labelText})} })

可以看到直線上每一個(gè)點(diǎn)的高度都比3D tiles上的高度高，顧能夠看到。

2、基于DEM通視

tip:同理，比較地形上的高度，與線段上的高度。

// 獲取經(jīng)緯度const startPoint = car3ToLatLon(points[0]);const endPoint = car3ToLatLon(points[1]);// const h_asc = (startPoint.height >= endPoint.height) ? false : true; //兩個(gè)點(diǎn) 哪個(gè)點(diǎn)高const pointSum = this.pointsNumlet pts:[number,number,number][] = []let cartesians = new Array(pointSum);let offset, x, y, height;for (let i = 0; i< pointSum; ++i) {offset = i / (pointSum - 1)x = Cesium.Math.lerp(startPoint.lon, endPoint.lon, offset)y = Cesium.Math.lerp(startPoint.lat, endPoint.lat, offset)height = Cesium.Math.lerp(startPoint.height, endPoint.height, offset)pts.push([x, y, height])//使用提供的笛卡爾坐標(biāo)計(jì)算t處的線性插值或外推(開始點(diǎn)，結(jié)束點(diǎn)，插值多少，存儲(chǔ)在哪)cartesians[i] = Cesium.Cartesian3.lerp(points[0], points[1], offset, new Cesium.Cartesian3())}const cartesians_clone = cartesians.map(d => d.clone())const terrainProvider = Cesium.createWorldTerrain() //加載高程地址 可以是自定義的const positions = pts.map(d=> Cesium.Cartographic.fromDegrees(...d))//根據(jù)地形算某經(jīng)緯點(diǎn)的高度//查詢完成后，可解析為提供的位置列表的承諾。這個(gè) 如果地形提供商的`availability`屬性未定義，則promise將拒絕const promise:any = Cesium.sampleTerrainMostDetailed(terrainProvider, positions);(<any>Cesium).when(promise, (updatedPositions: any)=> {//可視終點(diǎn)let line_s_index = 0, position_updated = null, heightArr:number[] = [], entityHeightArr = [];const length = updatedPositions.length-1for (let i = 1; i < length; i++) {const position_updated = updatedPositions[i]entityHeightArr.push( position_updated.height)heightArr.push(pts[i][2])}this.heightArr = heightArrthis.entityHeightArr = entityHeightArrfor (let i = 1; i < length; i++) {position_updated = updatedPositions[i]if(!line_s_index && position_updated && position_updated.height > pts[i][2]) {line_s_index = ibreak;}}let line_e_index = line_s_index;if (callback) {this.isTrue = !!line_s_indexconst labelText = `起點(diǎn)坐標(biāo)：${startPoint.lon.toFixed(2)} | ${startPoint.lat.toFixed(2)}| ${startPoint.height.toFixed()}\n終點(diǎn)坐標(biāo)：${endPoint.lon.toFixed(2)} | ${endPoint.lat.toFixed(2)}| ${endPoint.height.toFixed()}\n通視結(jié)果: ${line_s_index > 0 ? '否' : '是'}`callback({'line_s_end': cartesians_clone[line_s_index],'line_e_start': cartesians_clone[line_e_index],'labelResult': labelText})}})

• 當(dāng)然插值越多，計(jì)算出來的結(jié)果就越接近準(zhǔn)確值。

總結(jié)

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