cesium限制相机高度，避免穿地

const minimumHeight = 120;//单位米

  /**
       * 限制相机高度
       * todo https://blog.csdn.net/gnibuoz/article/details/102505433
       */
      limitCameraHeight(){
        // 在渲染阶段前添加事件监听器
        viewer.scene.preRender.addEventListener(function () {
          var eye = viewer.camera.positionCartographic;
          console.log('当前高度--->：',eye.height)
          // 判断相机坐标是否小于阈值，若小于阈值，则保持视点方位，修改相机高度
          // if (eye.height < minimumHeight) {
          if (eye.height < minimumHeight) {
            // console.log('限制相机高度:当前高度：',eye.height)
            viewer.camera.setView({
              destination: Cesium.Cartesian3.fromRadians(eye.longitude, eye.latitude, minimumHeight),
              // destination: Cesium.Cartesian3.fromRadians(eye.longitude, eye.latitude, 6500),
              orientation: {
                direction: viewer.camera.direction,
                up: viewer.camera.up
              }
            });
          }
        });
      },