Merge pull request #183 from Drangeer/measure

fix(measure):修改量测中间点计算方式和贴地多边形坐标获取错误

src/modules/math/midCartesian.js

 import { Cesium } from '../../namespace'
 
 export default function midCartesian(start, end) {
-  let c1 = Cesium.Ellipsoid.WGS84.cartesianToCartographic(start)
-  let c2 = Cesium.Ellipsoid.WGS84.cartesianToCartographic(end)
-  let cm = new Cesium.EllipsoidGeodesic(c1, c2).interpolateUsingFraction(0.5)
-  return Cesium.Ellipsoid.WGS84.cartographicToCartesian(cm)
+  return Cesium.Cartesian3.midpoint(start, end, new Cesium.Cartesian3())
 }

src/modules/measure/draw/DrawPolygon.js

         ...this._style,
         hierarchy: new Cesium.CallbackProperty(() => {
           if (this._positions.length > 2) {
-            return new Cesium.PolygonHierarchy(this._positions)
+            return new Cesium.PolygonHierarchy(
+              this._positions.map((item) => item.clone())
+            )
           } else {
             return null
           }

src/modules/measure/type/DistanceSurface.js

    */
   start(measure, options) {
     this._startHook(measure, options)
-    this._startLabel.label.heightReference =
-      Cesium.HeightReference.CLAMP_TO_GROUND
-    this._resultLabel.label.heightReference =
-      Cesium.HeightReference.CLAMP_TO_GROUND
     new DrawPolyline({
       material: options.material || Cesium.Color.YELLOW.withAlpha(0.6),
       depthFailMaterial: