Open Layer remove passed line when marker moves

Question

I'm working with open layer I have stumbled on a problem.

Here is what am I trying to achieve is to remove passed line, when the marker moves.

To explain a bit more, check bellow example:

https://openlayers.org/en/latest/examples/feature-move-animation.html

When clicking start animation, the marker moves, but the yellow line that marker passed by, is stayed, I would like to remove that line behind the marker when the marker moves.

How can that be done with OpenLayers?

Answer 1

Starting from the example referenced, one option would be to add a new line Feature, then update its coordinates to remove those which have already been traversed

• add a new Polyline:

  // new line feature (polyline) 
  var lineCoords = route.getCoordinates();
  var lineFeature = new ol.Feature({
    type: 'line',
    geometry: route.clone()
  });
  

• add the new feature to the vector layer:

  var vectorLayer = new ol.layer.Vector({ // VectorLayer({
    source: new ol.source.Vector({ // VectorSource({
      features: [geoMarker, startMarker, endMarker, lineFeature],
  

• inside the moveFeature function, update the line's coordinates to remove those already traversed:

  var moveFeature = function (event) {
      // ...
      var currentPoint = new ol.geom.Point(routeCoords[index]);
      coords=routeCoords.slice(index);
      lineFeature.getGeometry().setCoordinates(coords);
  

working example

code snippet:

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// It is usually loaded with AJAX.
var polyline = [
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  'Ngn@{PmhEwaA{SeF_u@kQuyAw]wQeEgtAsZ}LiCarAkVwI}D??_}RcjEinPspDwSqCgs@',
  'sPua@_OkXaMeT_Nwk@ob@gV}TiYs[uTwXoNmT{Uyb@wNg]{Nqa@oDgNeJu_@_G}YsFw]k',
  'DuZyDmm@i_@uyIJe~@jCg|@nGiv@zUi_BfNqaAvIow@dEed@dCcf@r@qz@Egs@{Acu@mC',
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var route = /** @type {import("../src/ol/geom/LineString.js").default} */ (new ol.format.Polyline({
  factor: 1e6,
}).readGeometry(polyline, {
  dataProjection: 'EPSG:4326',
  featureProjection: 'EPSG:3857',
}));

var routeCoords = route.getCoordinates();
var routeLength = routeCoords.length;

var routeFeature = new ol.Feature({
  type: 'route',
  geometry: route,
});
var lineCoords = route.getCoordinates();
var lineFeature = new ol.Feature({
  type: 'line',
  geometry: route.clone()
});
var geoMarker = /** @type Feature<import("../src/ol/geom/Point").default> */ (new ol.Feature({
  type: 'geoMarker',
  geometry: new ol.geom.Point(routeCoords[0]),
}));
var startMarker = new ol.Feature({
  type: 'icon',
  geometry: new ol.geom.Point(routeCoords[0]),
});
var endMarker = new ol.Feature({
  type: 'icon',
  geometry: new ol.geom.Point(routeCoords[routeLength - 1]),
});

var styles = {
  'line': new ol.style.Style({
    stroke: new ol.style.Stroke({
      width: 6,
      color: "blue",
    }),
  }),
  'route': new ol.style.Style({
    stroke: new ol.style.Stroke({
      width: 6,
      color: [237, 212, 0, 0.8],
    }),
  }),
  'icon': new ol.style.Style({
    image: new ol.style.Icon({
      anchor: [0.5, 1],
      src: 'https://openlayers.org/en/v4.6.5/examples/data/icon.png',
    }),
  }),
  'geoMarker': new ol.style.Style({
    image: new ol.style.Circle({ // CircleStyle({
      radius: 7,
      fill: new ol.style.Fill({
        color: 'black'
      }),
      stroke: new ol.style.Stroke({
        color: 'white',
        width: 2,
      }),
    }),
  }),
};

var animating = false;
var speed, now;
var speedInput = document.getElementById('speed');
var startButton = document.getElementById('start-animation');

var vectorLayer = new ol.layer.Vector({ // VectorLayer({
  source: new ol.source.Vector({ // VectorSource({
    features: [ /* routeFeature, */ geoMarker, startMarker, endMarker, lineFeature],
  }),
  style: function(feature) {
    // hide geoMarker if animation is active
    if (animating && feature.get('type') === 'geoMarker') {
      return null;
    }
    return styles[feature.get('type')];
  },
});

var key = 'otwSpfI7kCJve6AMTcr0';
var attributions =
  '<a href="https://www.maptiler.com/copyright/" target="_blank">&copy; MapTiler</a> ' +
  '<a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap contributors</a>';

var center = [-5639523.95, -3501274.52];
var map = new ol.Map({
  target: document.getElementById('map'),
  view: new ol.View({
    center: center,
    zoom: 10,
    minZoom: 2,
    maxZoom: 19,
  }),
  layers: [
    new ol.layer.Tile({ // TileLayer({
      source: new ol.source.XYZ({
        attributions: attributions,
        url: 'https://api.maptiler.com/maps/hybrid/{z}/{x}/{y}.jpg?key=' + key,
        tileSize: 512,
      }),
    }),
    vectorLayer
  ],
});

var moveFeature = function(event) {
  var vectorContext = ol.render.getVectorContext(event);
  var frameState = event.frameState;

  if (animating) {
    var elapsedTime = frameState.time - now;
    // here the trick to increase speed is to jump some indexes
    // on lineString coordinates
    var index = Math.round((speed * elapsedTime) / 1000);

    if (index >= routeLength) {
      stopAnimation(true);
      return;
    }

    var currentPoint = new ol.geom.Point(routeCoords[index]);
    coords = routeCoords.slice(index);
    lineFeature.getGeometry().setCoordinates(coords);
    var feature = new ol.Feature(currentPoint);
    vectorContext.drawFeature(feature, styles.geoMarker);
  }
  // tell OpenLayers to continue the postrender animation
  map.render();
};

function startAnimation() {
  if (animating) {
    stopAnimation(false);
  } else {
    animating = true;
    now = new Date().getTime();
    speed = speedInput.value;
    startButton.textContent = 'Cancel Animation';
    // hide geoMarker
    geoMarker.setStyle(null);
    // just in case you pan somewhere else
    map.getView().setCenter(center);
    vectorLayer.on('postrender', moveFeature);
    map.render();
  }
}

/**
 * @param {boolean} ended end of animation.
 */
function stopAnimation(ended) {
  animating = false;
  startButton.textContent = 'Start Animation';

  // if animation cancelled set the marker at the beginning
  var coord = ended ? routeCoords[routeLength - 1] : routeCoords[0];
  var geometry = geoMarker.getGeometry();
  geometry.setCoordinates(coord);
  //remove listener
  vectorLayer.un('postrender', moveFeature);
}

startButton.addEventListener('click', startAnimation, false);

html,
body {
  height: 100%;
  width: 100%;
  padding: 0px;
  margin: 0px;
}

.map {
  height: 90%;
  width: 100%;
}

<link rel="stylesheet" href="https://openlayers.org/en/v6.4.3/css/ol.css" type="text/css">
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://openlayers.org/en/v6.4.3/build/ol.js" type="text/javascript"></script>
<div id="map" class="map"></div>
<label for="speed">
      speed:&nbsp;
      <input id="speed" type="range" min="10" max="999" step="10" value="60">
    </label>
<button id="start-animation">Start Animation</button>