maptalks 开发GIS地图（37）maptalks.three.30- custom-linetrail

1. 尾线效果，很适合做轨迹追踪或者路线动画。

2. 数据使用 ./data/lines.json 

3. 处理数据

var lineStrings = geojson.map(function (feature) {
                    var coordinates = feature.coordinates;
                    var [from, to] = coordinates;
                    var lnglats = [[parseFloat(from[0]), parseFloat(from[1])], [parseFloat(to[0]), parseFloat(to[1])]]
                    return new maptalks.LineString(lnglats);
                });

4. 将数据处理为 linetrail 并添加到 图层。

                var offset = 2000;
                lineTrails = list.slice(0, offset).map(d => {
                    var line = new LineTrail(d.lineString, {
                        chunkLength: d.len / 100,
                        trail: 5,
                        speed: 1,
                        altitude: 100,
                    }, material, threeLayer)
                    return line;
                });
                var lines = list.slice(0, offset).map(d => {
                    return threeLayer.toLine(d.lineString, {}, lineMaterial);
                });

5. lineTrail 的自定义扩展类

//default values
        var OPTIONS = {
            trail: 5,
            chunkLength: 50,
            speed: 1,
            altitude: 0,
            interactive: false
        };

        const MAX_POINTS = 1000;

        /**
         * custom component
         * */

        class LineTrail extends maptalks.BaseObject {
            constructor(lineString, options, material, layer) {
                options = maptalks.Util.extend({}, OPTIONS, options, { layer, lineString });
                super();
                //Initialize internal configuration
                // https://github.com/maptalks/maptalks.three/blob/1e45f5238f500225ada1deb09b8bab18c1b52cf2/src/BaseObject.js#L135
                this._initOptions(options);

                const { altitude, chunkLength, speed, trail } = options;
                const chunkLines = lineSlice(lineString, chunkLength);


                const centerPt = layer.coordinateToVector3(lineString.getCenter());
                //cache position for  faster computing,reduce double counting
                const positionMap = {};
                for (let i = 0, len = chunkLines.length; i < len; i++) {
                    const chunkLine = chunkLines[i];
                    for (let j = 0, len1 = chunkLine.length; j < len1; j++) {
                        const lnglat = chunkLine[j];
                        const key = lnglat.join(',').toString();
                        if (!positionMap[key]) {
                            positionMap[key] = layer.coordinateToVector3(lnglat).sub(centerPt);
                        }
                    }
                }

                const positions = getChunkLinesPosition([chunkLines[0]], layer, positionMap, centerPt).positions;
                const geometry = new THREE.BufferGeometry();
                const ps = new Float32Array(MAX_POINTS * 3); // 3 vertices per point
                geometry.addAttribute('position', new THREE.BufferAttribute(ps, 3).setDynamic(true));
                setLineGeometryAttribute(geometry, positions);
                this._createLine(geometry, material);

                //set object3d position
                const z = layer.distanceToVector3(altitude, altitude).x;

                const center = lineString.getCenter();
                const v = layer.coordinateToVector3(center, z);
                this.getObject3d().position.copy(v);

                this._params = {
                    trail: Math.max(1, trail),
                    index: 0,
                    len: chunkLines.length,
                    chunkLines,
                    layer,
                    speed: Math.min(1, speed),
                    idx: 0,
                    positions: [],
                    positionMap,
                    centerPt
                };
                // this._init();
            }


            _init() {
                const { len, chunkLines, layer, trail, positionMap, centerPt } = this._params;
                for (let i = 0; i < len; i++) {
                    const result = chunkLines.slice(i, i + trail);
                    const ps = getChunkLinesPosition(result, layer, positionMap, centerPt).positions;
                    this._params.positions[i] = ps;
                }
            }


            _animation() {
                const { index, positions, idx, speed, len, chunkLines, layer, trail, positionMap, centerPt } = this._params;
                const i = Math.round(index);
                if (i > idx) {
                    this._params.idx++;
                    let ps = positions[i];
                    if (!ps) {
                        const result = chunkLines.slice(i, i + trail);
                        ps = getChunkLinesPosition(result, layer, positionMap, centerPt).positions;
                        this._params.positions[i] = ps;
                    }
                    setLineGeometryAttribute(this.getObject3d().geometry, ps);
                    this.getObject3d().geometry.attributes.position.needsUpdate = true;
                }
                if (index >= len) {
                    this._params.index = -1;
                    this._params.idx = -1;
                }
                this._params.index += speed;
            }
        }

6. 页面效果

7. 源码地址

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