我如何以编程方式调整 Cesium 承诺方法中元素的高度。

Question

我正在尝试移动从 cesium.js 中的 geojson 文件加载的实体的元素高度。我正在使用来自 Cesium Workshop /的示例 App.js 文件

我将如何修改下面的代码以调整数据实体的高度，以便将它们固定到地形的高程。我拥有的 geojson 文件的高度值为 0。此高度需要与该位置的地形相匹配。当我渲染这些数据时，许多点都在地形下。我假设我还需要查找地形高度，将数据转换为笛卡尔坐标来回协调到极坐标以将偏移量添加到实体中。

var geojsonOptions = {
        clampToGround : true
    };
 
 
 var testLinePromise = Cesium.GeoJsonDataSource.load('./Source/SampleData/testLines.geojson', geojsonOptions);

    // Save an new entity collection of neighborhood data
    var testLines;
    testLinePromise.then(function(dataSource) {
        // Add the new data as entities to the viewer
        viewer.dataSources.add(dataSource);
        testLines = dataSource.entities;

        // Get the array of entities
        var testLineEntities = dataSource.entities.values;
        for (var i = 0; i < testLineEntities.length; i++) {
            var entity = testLineEntities[i];

            if (Cesium.defined(entity.polygon)) {


                // Tells the polygon to color the terrain. ClassificationType.CESIUM_3D_TILE will color the 3D tileset, and ClassificationType.BOTH will color both the 3d tiles and terrain (BOTH is the default)
                entity.polygon.classificationType = Cesium.ClassificationType.TERRAIN;
                // Generate Polygon center
                var polyPositions = entity.polygon.hierarchy.getValue(Cesium.JulianDate.now()).positions;
                var polyCenter = Cesium.BoundingSphere.fromPoints(polyPositions).center;
                polyCenter = Cesium.Ellipsoid.WGS84.scaleToGeodeticSurface(polyCenter);
                entity.position = polyCenter;
                // Generate labels
                entity.label = {
                    text : entity.name,
                    showBackground : true,
                    scale : 0.6,
                    horizontalOrigin : Cesium.HorizontalOrigin.CENTER,
                    verticalOrigin : Cesium.VerticalOrigin.BOTTOM,
                    distanceDisplayCondition : new Cesium.DistanceDisplayCondition(10.0, 8000.0),
                    disableDepthTestDistance : 100.0
                };
            }
        }
    });

这是geojson文件

    {
      "type": "FeatureCollection",
      "features": [
        {
          "type": "Feature",
          "properties": {
            "name": "623dd9c1-26cb-4248-8e41-ebc8c3a16af5",
            "description": "descr A",
            "company": "ACME"
          },
          "geometry": {
            "type": "LineString",
            "coordinates": [
              [
                -114.5305072,
                20.61238237,
                0
              ],
              [
                -111.9486,
                10.46916111,
                0
              ]
            ]
          }
        },
        {
          "type": "Feature",
          "properties": {
            "name": "15966b86-26d0-4e0b-ba6e-7fa0c98bfe5e",
            "description": "descr C",
            "company": "ACME"
          },
          "geometry": {
            "type": "LineString",
            "coordinates": [
              [
                -135.9989702,
                45.7677603,
                0
              ],
              [
                -134.5305072,
                50.61238237,
                0
              ]
            ]
          }
        },
        {
          "type": "Feature",
          "properties": {
            "name": "00ca37f5-de78-4d5b-88b5-d39808ff8143",
            "description": "descr D",
            "company": "ACME"
          },
          "geometry": {
            "type": "LineString",
            "coordinates": [
              [
                -125.9989702,
                65.7677603,
                0
              ],
              [
                -129.0238961,
                67.96685,
                0
              ]
            ]
          }
        },
        {
          "type": "Feature",
          "properties": {
            "name": "22e5e02f-fa43-445e-a2eb-29ad760a964c",
            "description": "descr E",
            "company": "ACME"
          },
          "geometry": {
            "type": "LineString",
            "coordinates": [
              [
                -105.9989702,
                55.7677603,
                0
              ],
              [
                -100.7366501,
                55.67798889,
                0
              ]
            ]
          }
        },
        {
          "type": "Feature",
          "properties": {
            "name": "c4aefe46-a2a6-4a97-ac36-571c9e370d31",
            "description": "descr A",
            "company": "ACME"
          },
          "geometry": {
            "type": "LineString",
            "coordinates": [
              [
                -111.994653,
                78.84398434,
                0
              ],
              [
                -128.4816326,
                16.68839404,
                0
              ]
            ]
          }
        }
      ]
    }