javascript - 如何从openlayers中连续的数组点绘制线串

Question

我试图在 openlayers 中使用连续的 Points 绘制 LineString 以赋予它动画的感觉，就像它从头到尾绘制一样。

我试图通过关注 this example 来实现它. OL2 的所有引用都转换为 OpenLayers 5，但绘制仍然应该发生一个点，然后是整个数组的下一个点，而不是一次。

在此处查找具有当前输出的代码 - my code .

[供引用] 这是我正在努力实现的Snake animation for leaflet .

Answer 1

仅使用线串的顶点不会产生流畅的动画。您可以在 OpenLayers 示例中看到 https://openlayers.org/en/v4.6.5/examples/feature-move-animation.html标记在直线部分移动得更快。如果您需要像 OpenLayers 2 示例中那样沿着直线平滑移动，您需要使用 .getCoordinateAt() 随时计算您应该在直线上的位置。这是一个基于标记动画示例的演示，但也计算显示蛇示例中的线串的顶点之间的位置。您还可以绘制自己的直线并观看它们的动画效果。

var style = new ol.style.Style({
  stroke: new ol.style.Stroke({
width: 4,
color: 'red'
  })
});

var raster = new ol.layer.Tile({
  source:  new ol.source.OSM()
});

var vector = new ol.layer.Vector({
  source: new ol.source.Vector(),
  style: style
});

var map = new ol.Map({
  layers: [raster, vector],
  target: 'map',
  view: new ol.View()
});

var xhr = new XMLHttpRequest();
xhr.open('GET', 'https://raw.githubusercontent.com/IvanSanchez/Leaflet.Polyline.SnakeAnim/master/route.js');
xhr.onload = function() {
  // read the route coordinates
  eval(xhr.responseText);
  // reverse the route
  var geom = new ol.geom.LineString(route.reverse());
  // change Lat/Lon to Lon/Lat
  geom.applyTransform(function(c){ return c.reverse(); });
  geom.transform('EPSG:4326', map.getView().getProjection());
  map.getView().fit(geom.getExtent(), { size: map.getSize() });
  var snake = new ol.Feature();
  vector.getSource().addFeature(snake);
  animate_line(snake, geom, 30000);
}
xhr.send();

function animate_line(feature, linestring, duration) {

  var length = linestring.getLength();
  var length_shown = 0;

  var coords = linestring.getCoordinates();
  var coords_shown = [coords[0], coords[0]];
  var geom_shown = new ol.geom.LineString(coords_shown);
  feature.setGeometry(geom_shown);

  var coordcount = 1;
  var start = new Date().getTime();
  var listenerKey = map.on('postcompose', animate);

  function animate() {

var elapsed = new Date().getTime() - start;
var toAdd = length*elapsed/duration - length_shown;
var point = linestring.getCoordinateAt(Math.min(elapsed/duration, 1));

// restart from last intermediate point and remove it
var newPart = new ol.geom.LineString(coords_shown.slice(-1));
coords_shown.pop();

// add vertices until required length exceeded
while (coordcount < coords.length && newPart.getLength() <= toAdd) {
  newPart.appendCoordinate(coords[coordcount]);
  coords_shown.push(coords[coordcount]);
  coordcount++;
}

// replace overrun vertex with intermediate point
coords_shown.pop();
coordcount--;
coords_shown.push(point);

geom_shown.setCoordinates(coords_shown);
length_shown += toAdd;

if (elapsed > duration) {
  ol.Observable.unByKey(listenerKey);
}
map.render();

  }

}

draw = new ol.interaction.Draw({
  source: vector.getSource(),
  type: 'LineString'
});

draw.on('drawend',function(evt){
  geom = evt.feature.getGeometry();
  evt.feature.setGeometry(undefined);
  animate_line(evt.feature, geom, 6000);
});
map.addInteraction(draw);

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

<link href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" rel="stylesheet" />
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<div id="map" class="map"></div>