cesium压平实现代码

以下是Cesium压平实现代码的示例：

// 获取模型的顶点
var positions = model.geometry.attributes.position.values;

// 计算模型的中心点
var center = Cesium.BoundingSphere.fromVertices(positions).center;

// 将顶点转换为笛卡尔坐标
for (var i = 0; i < positions.length; i += 3) {
  var position = Cesium.Cartesian3.fromArray(positions, i);
  positions[i] = position.x - center.x;
  positions[i + 1] = position.y - center.y;
  positions[i + 2] = position.z - center.z;
}

// 压平模型
Cesium.Matrix4.multiplyByTranslation(
  model.modelMatrix,
  center,
  model.modelMatrix
);
model.readyPromise.then(function (model) {
  var boundingSphere = model.boundingSphere;
  var height = boundingSphere.radius;
  var plane = new Cesium.Plane(
    new Cesium.Cartesian3(0, 0, 1),
    -height
  );
  var translation = Cesium.Transforms.eastNorthUpToFixedFrame(
    boundingSphere.center
  );
  var rotation = Cesium.Quaternion.fromRotationMatrix(translation);
  var transform = Cesium.Matrix4.fromRotationTranslation(
    rotation,
    Cesium.Cartesian3.ZERO
  );
  var inverseTransform = Cesium.Matrix4.inverse(transform, new Cesium.Matrix4());
  var planeProjection = new Cesium.Matrix4();
  Cesium.Matrix4.multiply(
    inverseTransform,
    translation,
    planeProjection
  );
  Cesium.Matrix4.multiply(
    planeProjection,
    transform,
    planeProjection
  );
  Cesium.Matrix4.multiply(
    model.modelMatrix,
    planeProjection,
    model.modelMatrix
  );
});

这段代码首先获取了3D模型的顶点，然后计算模型的中心点，并将顶点转换为笛卡尔坐标。接下来，通过Cesium的Matrix4.multiplyByTranslation方法将模型转换为以中心点为原点的坐标系。

最后，通过Cesium.Plane对象创建一个平面，将模型投影到该平面上，并将投影后的模型与原始模型进行合并，从而实现压平效果。