maptalks 开发GIS地图（43）maptalks.three.36- custom-rgbimage-terrain-landscape

1.  这个最终效果有点像地形图的热力图了，高的地方颜色深，矮的地方颜色浅，用到合适的地方效果也不错吧。AR VR 三维地图以后使用的场景应该会越来越多吧。

2.  地形图数据使用的是 ./data/west-lake-area.geojson

　  RGBImage 使用的是 mapbox 的数据，

                const url = `https://a.tiles.mapbox.com/v4/mapbox.terrain-rgb/${z}/${x}/${y}.pngraw?access_token=${accesstoken}`;

 Texture 使用的也是mapbox 的数据

                const url = `https://api.mapbox.com/v4/mapbox.satellite/${z}/${x}/${y}.webp?sku=101XzrMiclXn4&access_token=${accesstoken}`;

3. 使用 Terrain 扩展类来计算对应的高度。

 class Terrain extends maptalks.BaseObject {
            constructor(extent, options, material, layer) {
                options = maptalks.Util.extend({}, OPTIONS, options, { layer, extent });
                const { texture, image, altitude, imageHeight, imageWidth, factor, filterIndex } = options;
                if (!image) {
                    console.error('not find image');
                }
                if (!(extent instanceof maptalks.Extent)) {
                    extent = new maptalks.Extent(extent);
                }
                const { xmin, ymin, xmax, ymax } = extent;
                const coords = [
                    [xmin, ymin],
                    [xmin, ymax],
                    [xmax, ymax],
                    [xmax, ymin]
                ];
                let vxmin = Infinity, vymin = Infinity, vxmax = -Infinity, vymax = -Infinity;
                coords.forEach(coord => {
                    const v = layer.coordinateToVector3(coord);
                    const { x, y } = v;
                    vxmin = Math.min(x, vxmin);
                    vymin = Math.min(y, vymin);
                    vxmax = Math.max(x, vxmax);
                    vymax = Math.max(y, vymax);
                });
                const w = Math.abs(vxmax - vxmin), h = Math.abs(vymax - vymin);
                const rgbImg = generateImage(image), img = generateImage(texture);
                const geometry = new THREE.PlaneBufferGeometry(w, h, imageWidth - 1, imageHeight - 1);
                super();
                this._initOptions(options);
                this._createMesh(geometry, material);
                const z = layer.distanceToVector3(altitude, altitude).x;
                const v = layer.coordinateToVector3(extent.getCenter(), z);
                this.getObject3d().position.copy(v);
                material.transparent = true;
                if (rgbImg) {
                    material.opacity = 0;
                    rgbImg.onload = () => {
                        const width = imageWidth, height = imageHeight;
                        const imgdata = getRGBData(rgbImg, width, height);
                        let idx = 0;
                        let maxZ = -Infinity;
                        //rgb to height  https://docs.mapbox.com/help/troubleshooting/access-elevation-data/
                        for (let i = 0, len = imgdata.length; i < len; i += 4) {
                            const R = imgdata[i], G = imgdata[i + 1], B = imgdata[i + 2];
                            const height = -10000 + ((R * 256 * 256 + G * 256 + B) * 0.1);
                            const z = layer.distanceToVector3(height, height).x * factor;
                            geometry.attributes.position.array[idx * 3 + 2] = z;
                            maxZ = Math.max(z, maxZ);
                            idx++;
                        }
                        this.getOptions().maxZ = maxZ;
                        geometry.attributes.position.needsUpdate = true;
                        if (filterIndex) {
                            const _filterIndex = [];
                            const index = geometry.getIndex().array;
                            const position = geometry.attributes.position.array;
                            const z = maxZ / 15;
                            for (let i = 0, len = index.length; i < len; i += 3) {
                                const a = index[i];
                                const b = index[i + 1];
                                const c = index[i + 2];
                                const z1 = position[a * 3 + 2];
                                const z2 = position[b * 3 + 2];
                                const z3 = position[c * 3 + 2];
                                if (z1 > z || z2 > z || z3 > z) {
                                    _filterIndex.push(a, b, c);
                                }
                            }
                            geometry.setIndex(new THREE.Uint32BufferAttribute(_filterIndex, 1));
                        }
                        if (img) {
                            textureLoader.load(img.src, (texture) => {
                                material.map = texture;
                                material.opacity = 1;
                                material.needsUpdate = true;
                                this.fire('load');
                            });
                        } else {
                            material.opacity = 1;
                        }
                    };
                    rgbImg.onerror = function () {
                        console.error(`not load ${rgbImg.src}`);
                    };
                }
            }
        }

4. 页面显示

5. 源码地址

https://github.com/WhatGIS/maptalkMap/tree/main/threelayer/demo