javascript - 如何在铯地形上添加标记

Question

为了在铯中的地形上添加标记，我使用了 sampleTerrain获取高度的函数。

我可以在山顶上添加标记，但标记距离鼠标点击位置很远。如何在 Cesium 地形上添加标记，以便将标记准确添加到单击的位置？

为了引用，我会把我的代码放在这里:

async leftClickInputAction(event:{position: {x:number, y:number}}):Promise<any> {

let positionCartesian3 = this.cesium.viewer.camera.pickEllipsoid(event.position);
let positionCartographic = Cesium.Cartographic.fromCartesian(positionCartesian3);
await Cesium.sampleTerrain(this.cesium.viewer.terrainProvider, 9, [positionCartographic]);

let height = positionCartographic.height;
let cart3_with_height = Cesium.Cartesian3.fromRadians(positionCartographic.longitude, positionCartographic.latitude, positionCartographic.height );
let window_coordinates = this.cesium.calcService.toFixes7Obj(Cesium.SceneTransforms.wgs84ToWindowCoordinates(this.cesium.viewer.scene,cart3_with_height));
positionCartesian3 = this.cesium.viewer.camera.pickEllipsoid(event.position);
positionCartographic = Cesium.Cartographic.fromCartesian(positionCartesian3);
positionCartographic.height = height;*/

let lngDeg:number = Cesium.Math.toDegrees(positionCartographic.longitude);
let latDeg:number = Cesium.Math.toDegrees(positionCartographic.latitude);
let position: [number, number, number] = [lngDeg, latDeg, positionCartographic.height];
let color:string = this.cesium.positionFormService.getSelectedColor();
let marker_picker = {position};
if(color != "blue") marker_picker['color'] = color;
this.cesium.queryParamsHelperService.addMarker(marker_picker);

Answer 1

这一行是你的问题:

    let positionCartesian3 = this.cesium.viewer.camera.pickEllipsoid(event.position);

pickEllipsoid 函数从 WGS84 椭球体中选取值(认为“类似于海平面”，但不要将其与实际 MSL 混淆)。此函数永远不会从山顶返回一个点。

当然，您通过调用 sampleTerrain 增强了此功能，这很好，但没有解决问题。 “选择”错过了山顶，最终选择了远低于山后的椭圆体上的一个点，而不是用户认为他们点击的地方附近。

您可以使用另一个函数，viewer.scene.pickPosition ，这将通过从 WebGL 的深度缓冲区中读取它们来返回位置。这意味着该功能仅在近距离范围内可靠，例如当相机足够近以看到单个山脉时，而不是缩小到整个地球。但它确实可以让您选择山顶等。

Here's a Sandcastle demo .它使用从 Picking Demo 中提取的代码并修改为在珠穆朗玛峰工作。

var terrain = Cesium.createDefaultTerrainProviderViewModels();
var viewer = new Cesium.Viewer('cesiumContainer', {
    animation: false,
    timeline: false,
    geocoder : false,
    selectionIndicator : false,
    infoBox : false,
    terrainProviderViewModels: terrain,
    selectedTerrainProviderViewModel: terrain[1]
});

function lookAtMtEverest() {
    var target = new Cesium.Cartesian3(300770.50872389384, 5634912.131394585, 2978152.2865545116);
    var offset = new Cesium.Cartesian3(6344.974098678562, -793.3419798081741, 2499.9508860763162);
    viewer.camera.lookAt(target, offset);
    viewer.camera.lookAtTransform(Cesium.Matrix4.IDENTITY);
}

lookAtMtEverest();

var labelEntity = viewer.entities.add({
    label : {
        show : false,
        showBackground : true,
        font : '14px monospace',
        horizontalOrigin : Cesium.HorizontalOrigin.LEFT,
        verticalOrigin : Cesium.VerticalOrigin.TOP,
        pixelOffset : new Cesium.Cartesian2(15, 0)
    }
});

var sceneModeWarningPosted = false;

// Mouse over the globe to see the cartographic position
var handler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);
handler.setInputAction(function(movement) {
    var foundPosition = false;
    var scene = viewer.scene;
    var pickedObject = scene.pick(movement.endPosition);
    if (scene.pickPositionSupported) {
        if (scene.mode === Cesium.SceneMode.SCENE3D) {
            var cartesian = viewer.scene.pickPosition(movement.endPosition);

            if (Cesium.defined(cartesian)) {
                var cartographic = Cesium.Cartographic.fromCartesian(cartesian);
                var longitudeString = Cesium.Math.toDegrees(cartographic.longitude).toFixed(3);
                var latitudeString = Cesium.Math.toDegrees(cartographic.latitude).toFixed(3);
                var heightString = cartographic.height.toFixed(2);

                labelEntity.position = cartesian;
                labelEntity.label.show = true;
                labelEntity.label.text =
                    'Lon: ' + ('   ' + longitudeString).slice(-8) + '\u00B0' +
                    '\nLat: ' + ('   ' + latitudeString).slice(-8) + '\u00B0' +
                    '\nAlt: ' + ('   ' + heightString).slice(-7) + 'm';

                var camera = scene.camera;
                labelEntity.label.eyeOffset = new Cesium.Cartesian3(0.0, 0.0, camera.frustum.near * 1.5 - Cesium.Cartesian3.distance(cartesian, camera.position));

                foundPosition = true;
            }
        } else if (!sceneModeWarningPosted) {
            sceneModeWarningPosted = true;
            console.log("pickPosition is currently only supported in 3D mode.");
        }
    }

    if (!foundPosition) {
        labelEntity.label.show = false;
    }
}, Cesium.ScreenSpaceEventType.MOUSE_MOVE);