如何在銫地形上添加標記

Question

為了在 cesium 中的地形上添加標記，我使用了sampleTerrain函數來獲取高度。

我可以在山頂上添加一個標記，但該標記離鼠標點擊很遠。 如何在 Cesium 地形上添加標記，以便將標記准確添加到單擊位置？

作為參考，我將把我的代碼放在這里：

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

這一行是你的問題：

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

pickEllipsoid函數從 WGS84 橢球pickEllipsoid取值（認為“類似於海平面”，但不要將其與實際 MSL 混淆）。 這個函數永遠不會從山頂返回一個點。

當然，您通過調用sampleTerrain增強了此功能，這很好，但並沒有解決問題。 “pick”沒有到達山頂，最終在遠離山峰下方和后方的橢圓體上挑選一個點，而不是用戶認為他們點擊的位置附近。

您可以使用另一個函數viewer.scene.pickPosition ，它將通過從 WebGL 的深度緩沖區中讀取位置來返回位置。 這意味着該功能僅在近距離時可靠，例如當相機足夠近以看到單個山脈時，而不是縮小到整個地球。 但它確實讓你選擇山頂之類的。

這是一個 Sandcastle 演示。 它使用從Picking Demo 中提取並經過修改以在珠穆朗瑪峰上工作的代碼。

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);

Answer 2

我用過：

     let ray = this.cesium.viewer.camera.getPickRay(event.position);
      let positionCartesian3 = this.cesium.viewer.scene.globe.pick(ray, this.cesium.viewer.scene);
      let positionCartographic = Cesium.Cartographic.fromCartesian(positionCartesian3);
      let lngDeg: number = Cesium.Math.toDegrees(positionCartographic.longitude);
      let latDeg: number = Cesium.Math.toDegrees(positionCartographic.latitude);
       position = [lngDeg, latDeg, positionCartographic.height];