Cesium屏幕中心坐标和相机位置坐标计算

1.获取当前屏幕中心点的位置

    getCenterPosition() {
        let centerResult = viewer.camera.pickEllipsoid(
            new Cesium.Cartesian2(
                viewer.canvas.clientWidth / 2,
                viewer.canvas.clientHeight / 2,
            ),
        )
        centerPoint = centerResult;
        let curPosition = Cesium.Ellipsoid.WGS84.cartesianToCartographic(centerResult);
        let curLongitude = (curPosition.longitude * 180) / Math.PI;
        let curLatitude = (curPosition.latitude * 180) / Math.PI;
        return {
            lon: curLongitude,
            lat: curLatitude,
        }
        // }
    }

2.获取当前相机的位置

 getCameraPosition() {
        var position = viewer.scene.camera.positionCartographic;
        // 弧度转经纬度
        var longitude = Cesium.Math.toDegrees(position.longitude);
        var latitude = Cesium.Math.toDegrees(position.latitude);
        var height = position.height;
        return { lng: longitude, lat: latitude, h: height }
    }

3.绕非固定屏幕中心点旋转

moveRotation方法参数中第一个参数step是移动步长，第二个参数i是判断是否是俯仰角还是航向角进行绕中心点进行翻滚，entity可以另外分离出来做一个方法，这样避免每次调用moveRotation方法都生成一个entity覆盖物。

  moveRotation(step, i = 0) {
        // 添加实体
        let a = this.getCenterPosition();
        let b = this.getCameraPosition();
        entity = viewer.entities.add({
            position: new Cesium.Cartesian3.fromDegrees(a.lon, a.lat, 0),
            point: {
                pixelSize: 0,
                // show: false
            }
        });
        let clickPosition1 = Cesium.Cartesian3.fromDegrees(a.lon, a.lat, 0);
        let clickPosition2 = Cesium.Cartesian3.fromDegrees(b.lng, b.lat, b.h);
        // 计算两个点之间的距离
        let distancetemp = Cesium.Cartesian3.distance(clickPosition1, clickPosition2);
        // 距离远一些就将移动角度调整大一些
        if (i && distancetemp > 20000) {
            heading += 3 * step;
        } else if (i) {
            heading += step;
        } else if (!i && distancetemp > 20000) {
            pitch += 3 * step;
        } else if (!i) {
            pitch += step;
        }
       let offset = new Cesium.HeadingPitchRange(
            heading,
            pitch,
            distancetemp  // 相机距离地球球心的距离
        );
        viewer.zoomTo(entity, offset);
    }

4.相机位置在原地据法向量升起和下降 

该方法的参数distance接受正负数，对应上升和下降

   moveForward(distance) {
        var camera = viewer.camera;
        var direction = camera.direction;
        //获得此位置默认的向上方向
        var up = Cesium.Cartesian3.normalize(camera.position, new Cesium.Cartesian3());
        var right = Cesium.Cartesian3.cross(direction, up, new Cesium.Cartesian3());
        direction = Cesium.Cartesian3.cross(up, right, new Cesium.Cartesian3());
        direction = Cesium.Cartesian3.normalize(direction, direction);
        direction = Cesium.Cartesian3.multiplyByScalar(direction, distance, direction);
        camera.position = Cesium.Cartesian3.add(camera.position, direction, camera.position);
    }