Cesium 镜头飞至地表下后会看到破损的地表，影响用户体验，github上有人给出了解决方法，记录如下：

• github 问题讨论地址
• 代码：

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

var minPitch = -Cesium.Math.PI_OVER_TWO;

var maxPitch = 0;

var minHeight = 200;

viewer.camera.changed.addEventListener(

    function() {

        if (viewer.camera._suspendTerrainAdjustment && viewer.scene.mode === Cesium.SceneMode.SCENE3D) {

            viewer.camera._suspendTerrainAdjustment = false;

            viewer.camera._adjustHeightForTerrain();

        }

        // Keep camera in a reasonable pitch range

        var pitch = viewer.camera.pitch;

        if (pitch > maxPitch || pitch < minPitch) {

            viewer.scene.screenSpaceCameraController.enableTilt = false;

            // clamp the pitch

            if(pitch > maxPitch ) {

                pitch = maxPitch;

            } else if(pitch < minPitch) {

                pitch = minPitch;

            }

            var destination = Cesium.Cartesian3.fromRadians(

                viewer.camera.positionCartographic.longitude,

                viewer.camera.positionCartographic.latitude,

                Math.max(viewer.camera.positionCartographic.height, minHeight));

            viewer.camera.setView({

                destination: destination,

                orientation: { pitch: pitch }

            });

            viewer.scene.screenSpaceCameraController.enableTilt = true;

        }

    }

);