This example uses OpenLayers v10.9.0. The latest is v.
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#### IGC Data

complex-geometry 1 closest-feature 1 igc 3 opencyclemap 1

#####

Example of tracks recorded from multiple paraglider flights on the same day, read from an IGC file.

The five tracks contain a total of 49,707 unique coordinates. Zoom in to see more detail. The background layer is from OpenCycleMap.

##### main.js

    import Feature from 'ol/Feature.js';
    import Map from 'ol/Map.js';
    import View from 'ol/View.js';
    import IGC from 'ol/format/IGC.js';
    import LineString from 'ol/geom/LineString.js';
    import Point from 'ol/geom/Point.js';
    import TileLayer from 'ol/layer/Tile.js';
    import VectorLayer from 'ol/layer/Vector.js';
    import {getVectorContext} from 'ol/render.js';
    import OSM, {ATTRIBUTION} from 'ol/source/OSM.js';
    import VectorSource from 'ol/source/Vector.js';
    import CircleStyle from 'ol/style/Circle.js';
    import Fill from 'ol/style/Fill.js';
    import Stroke from 'ol/style/Stroke.js';
    import Style from 'ol/style/Style.js';

    const colors = {
      'Clement Latour': 'rgba(0, 0, 255, 0.7)',
      'Damien de Baesnt': 'rgba(0, 215, 255, 0.7)',
      'Sylvain Dhonneur': 'rgba(0, 165, 255, 0.7)',
      'Tom Payne': 'rgba(0, 255, 255, 0.7)',
      'Ulrich Prinz': 'rgba(0, 215, 255, 0.7)',
    };

    const styleCache = {};
    const styleFunction = function (feature) {
      const color = colors[feature.get('PLT')];
      let style = styleCache[color];
      if (!style) {
        style = new Style({
          stroke: new Stroke({
            color: color,
            width: 3,
          }),
        });
        styleCache[color] = style;
      }
      return style;
    };

    const vectorSource = new VectorSource();

    const igcUrls = [
      'data/igc/Clement-Latour.igc',
      'data/igc/Damien-de-Baenst.igc',
      'data/igc/Sylvain-Dhonneur.igc',
      'data/igc/Tom-Payne.igc',
      'data/igc/Ulrich-Prinz.igc',
    ];

    function get(url, callback) {
      const client = new XMLHttpRequest();
      client.open('GET', url);
      client.onload = function () {
        callback(client.responseText);
      };
      client.send();
    }

    const igcFormat = new IGC();
    for (let i = 0; i < igcUrls.length; ++i) {
      get(igcUrls[i], function (data) {
        const features = igcFormat.readFeatures(data, {
          featureProjection: 'EPSG:3857',
        });
        vectorSource.addFeatures(features);
      });
    }

    const time = {
      start: Infinity,
      stop: -Infinity,
      duration: 0,
    };
    vectorSource.on('addfeature', function (event) {
      const geometry = event.feature.getGeometry();
      time.start = Math.min(time.start, geometry.getFirstCoordinate()[2]);
      time.stop = Math.max(time.stop, geometry.getLastCoordinate()[2]);
      time.duration = time.stop - time.start;
    });

    const vectorLayer = new VectorLayer({
      source: vectorSource,
      style: styleFunction,
    });

    const map = new Map({
      layers: [
        new TileLayer({
          source: new OSM({
            attributions: [
              'All maps © <a href="https://www.opencyclemap.org/">OpenCycleMap</a>',
              ATTRIBUTION,
            ],
            url:
              'https://{a-c}.tile.thunderforest.com/cycle/{z}/{x}/{y}.png' +
              '?apikey=Your API key from https://www.thunderforest.com/docs/apikeys/ here',
          }),
        }),
        vectorLayer,
      ],
      target: 'map',
      view: new View({
        center: [703365.7089403362, 5714629.865071137],
        zoom: 9,
      }),
    });

    let point = null;
    let line = null;
    const displaySnap = function (coordinate) {
      const closestFeature = vectorSource.getClosestFeatureToCoordinate(coordinate);
      const info = document.getElementById('info');
      if (closestFeature === null) {
        point = null;
        line = null;
        info.innerHTML = '&nbsp;';
      } else {
        const geometry = closestFeature.getGeometry();
        const closestPoint = geometry.getClosestPoint(coordinate);
        if (point === null) {
          point = new Point(closestPoint);
        } else {
          point.setCoordinates(closestPoint);
        }
        const date = new Date(closestPoint[2] * 1000);
        info.innerHTML =
          closestFeature.get('PLT') + ' (' + date.toUTCString() + ')';
        const coordinates = [coordinate, [closestPoint[0], closestPoint[1]]];
        if (line === null) {
          line = new LineString(coordinates);
        } else {
          line.setCoordinates(coordinates);
        }
      }
      map.render();
    };

    map.on('pointermove', function (evt) {
      if (evt.dragging) {
        return;
      }
      const coordinate = map.getEventCoordinate(evt.originalEvent);
      displaySnap(coordinate);
    });

    map.on('click', function (evt) {
      displaySnap(evt.coordinate);
    });

    const stroke = new Stroke({
      color: 'rgba(255,0,0,0.9)',
      width: 1,
    });
    const style = new Style({
      stroke: stroke,
      image: new CircleStyle({
        radius: 5,
        fill: null,
        stroke: stroke,
      }),
    });
    vectorLayer.on('postrender', function (evt) {
      const vectorContext = getVectorContext(evt);
      vectorContext.setStyle(style);
      if (point !== null) {
        vectorContext.drawGeometry(point);
      }
      if (line !== null) {
        vectorContext.drawGeometry(line);
      }
    });

    const featureOverlay = new VectorLayer({
      source: new VectorSource(),
      map: map,
      style: new Style({
        image: new CircleStyle({
          radius: 5,
          fill: new Fill({
            color: 'rgba(255,0,0,0.9)',
          }),
        }),
      }),
    });

    const control = document.getElementById('time');
    control.addEventListener('input', function () {
      const value = parseInt(control.value, 10) / 100;
      const m = time.start + time.duration * value;
      vectorSource.forEachFeature(function (feature) {
        const geometry = feature.getGeometry();
        const coordinate = geometry.getCoordinateAtM(m, true);
        let highlight = feature.get('highlight');
        if (highlight === undefined) {
          highlight = new Feature(new Point(coordinate));
          feature.set('highlight', highlight);
          featureOverlay.getSource().addFeature(highlight);
        } else {
          highlight.getGeometry().setCoordinates(coordinate);
        }
      });
      map.render();
    });

##### index.html

    <!DOCTYPE html>
    <html lang="en">
      <head>
        <meta charset="UTF-8">
        <title>IGC Data</title>
        <link rel="stylesheet" href="node_modules/ol/ol.css">
        <style>
          .map {
            width: 100%;
            height: 400px;
          }
        </style>
      </head>
      <body>
        <div id="map" class="map"></div>
        <input id="time" type="range" value="0" steps="1" />
        <div id="info">&nbsp;</div>

        <script type="module" src="main.js"></script>
      </body>
    </html>

##### package.json

    {
      "name": "igc",
      "dependencies": {
        "ol": "10.9.0"
      },
      "devDependencies": {
        "vite": "^3.2.3"
      },
      "scripts": {
        "start": "vite",
        "build": "vite build"
      }
    }