铯路径到地形:连接2点的线在地形下方 [英] Cesium path onto terrain: line connecting 2 points goes under the terrain

问题描述

我有一条随着时间的流逝的道路. 我使用Cesium.sampleTerrain获取位置高程并将其悬垂在地形上. 问题是，即使所有点都在地形上，连接2个点的线有时也会在地形下. 如何在地形上同时悬垂连接线?

I have a path moving over time. I use Cesium.sampleTerrain to get positions elevation and drape them on the terrain. The problem is that, even if all points are on the terrain, the line connecting 2 points sometimes goes under the terrain. How can I do to drape also connecting lines on the terrain?

这是我的代码:

var promise = Cesium.sampleTerrain(terrainProvider, 14, positions);
Cesium.when(promise, function(updatedPositions) {
    var cartesianPositions = Cesium.Ellipsoid.WGS84.cartographicArrayToCartesianArray(updatedPositions);
    var sample = new Cesium.SampledPositionProperty();
    sample.setInterpolationOptions({
        interpolationDegree : 3,
        interpolationAlgorithm : Cesium.HermitePolynomialApproximation
    });

    $(cartesianPositions).each(function(index, cartPosition) {
        var time = Cesium.JulianDate.addSeconds(start, index*10, new Cesium.JulianDate());
        sample.addSample(time, cartPosition);

    })

    var target = viewer.entities.add({
        position: sample,
          path: {
            resolution: 60,
            material:Cesium.Color.BLUE,
            width: 4,
            trailTime: 422*10,
            leadTime: 0
          }
    });

});

推荐答案

就像马修说的那样； Cesium当前不支持在地形上悬垂的折线"类型 entity .

So like Matthew says; Cesium doesn't currently support a 'polyline' type entity with draping over terrain.

如果您发现Entity API不能满足您的需求，则可能值得深入研究较低级别的Primitives API，以获得更好的控制权-更具体地说，是

If you find that the Entity API isn't giving you what you need, it might be worth digging into the lower-level Primitives API to gain finer control - more specifically the GroundPrimitive geometry.

在其他人中； GroundPrimitives当前支持 CorridorGeometry .

Among others; GroundPrimitives currently support the CorridorGeometry.

我没有在Cesium中进行时态数据绘图的经验，但是我建议您考虑使用这种方法，而不是异步承诺方法，该方法(IMO)似乎更多是由于缺乏GroundPrimitive类型的解决方案而引起的.时间.

I have no experience with temporal data plotting within Cesium, but I would suggest you consider this approach rather than the async promise approach, which (IMO) seems like more of a hack born from the absence of a GroundPrimitive-type solution at the time.

下面是一个实际的GroundPrimitive示例(请注意，我们不需要任何z值):

Here's a crude example of a GroundPrimitive in action (note we don't need any z values):

var viewer = new Cesium.Viewer('cesiumContainer');

var corridorInstance = new Cesium.GeometryInstance({
   geometry : new Cesium.CorridorGeometry({
      vertexFormat : Cesium.VertexFormat.POSITION_ONLY,
      positions : Cesium.Cartesian3.fromDegreesArray([
         -122.26, 46.15,  
         -122.12, 46.26, 
      ]),
      width : 100
   }),
   id : 'myCorridor',
   attributes : {
      color : new Cesium.ColorGeometryInstanceAttribute(0.0, 1.0, 1.0, 0.5)
   }
});

var corridorPrimitive = new Cesium.GroundPrimitive({
   geometryInstance : corridorInstance
});

viewer.scene.primitives.add(corridorPrimitive);
viewer.camera.setView({
   destination: Cesium.Cartesian3.fromDegrees(-122.19, 46.20, 10000.0)
});

哪个会给你这个:

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