Question

我尝试了多种方式来显示功能标签，但未成功。

我定义了一个功能：

var pointFeature = new ol.Feature(wha, {label: "Airport"});

如何在功能的位置（纬度/经度）显示“机场”一词？

我是OpenLayers的新手，所以如果答案很简单，我深表歉意。这是完整的代码：

<!DOCTYPE html>
<html>
<head>
<title>IGC example</title>
<script src="https://code.jquery.com/jquery-1.11.2.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="http://openlayers.org/en/v3.10.1/css/ol.css" type="text/css">
<script src="http://openlayers.org/en/v3.10.1/build/ol.js"></script>

</head>
<body><div class="ALL">

<div class="container-fluid">

<div class="row-fluid">
  <div class="span12">
    <div id="map" class="map">
    </div>
    <input id="time" type="range" value="0" steps="1" />
    <div class="span4 offset4 pull-right">
      <div id="info" class="alert alert-success">
        &nbsp;
      </div>
    </div>
  </div>
</div>

</div></div>
<script>

            // Geometries
            var wha     = new ol.geom.Circle(ol.proj.transform([-96.1543889, 29.2542778], 'EPSG:4326', 'EPSG:3857'), 400);
            var circle  = new ol.geom.Circle(ol.proj.transform([-96.1543889, 29.2542778], 'EPSG:4326', 'EPSG:3857'), 6000 );
            var gloster = new ol.geom.Circle(ol.proj.transform([-96.0598000, 29.7285833], 'EPSG:4326', 'EPSG:3857'), 2000 );
            var eagle   = new ol.geom.Circle(ol.proj.transform([-96.3220667, 29.6004330], 'EPSG:4326', 'EPSG:3857'), 1000 );



            // Points for the lines
            var points = [[-96.1543889, 29.2542778],
                          [-96.0598000, 29.7285833],
                          [-96.3220667, 29.6004330],
                          [-96.1543889, 29.2542778]];


            for (var i = 0; i < points.length; i++) {
                points[i] = ol.proj.transform(points[i], 'EPSG:4326', 'EPSG:3857');
                }

                var featureLine = new ol.Feature({
                geometry: new ol.geom.LineString(points)
                });
            var vectorLine = new ol.source.Vector({});
            vectorLine.addFeature(featureLine);

            var vectorLineLayer = new ol.layer.Vector({
                source: vectorLine,
                style: new ol.style.Style({
                fill: new ol.style.Fill({ color: '#00FF00', weight: 4 }),
                stroke: new ol.style.Stroke({ color: '#00FF00', width: 2 })
                })
                });

            // Features
            var pointFeature = new ol.Feature(wha, {label: "Airport"});
            var circleFeature = new ol.Feature(circle);
            var glosterFeature = new ol.Feature(gloster);
            var eagleFeature = new ol.Feature(eagle);





            // Source and vector layer
            var vectorSource = new ol.source.Vector({
                projection: 'EPSG:4326',
                features: [pointFeature, circleFeature, glosterFeature, eagleFeature]
            });

            var style = new ol.style.Style({
                fill: new ol.style.Fill({
                    color: 'rgba(20, 100, 240, 0.3)'
                }),
                stroke: new ol.style.Stroke({
                    width: 3,
                    color: 'rgba(0, 100, 240, 0.8)'
                }),
                image: new ol.style.Circle({
                    fill: new ol.style.Fill({
                        color: 'rgba(55, 200, 150, 0.5)'
                    }),
                    stroke: new ol.style.Stroke({
                        width: 10,
                        color: 'rgba(55, 200, 150, 0.8)'
                    }),
                    radius: 7
                }),
                text: new ol.style.Text(),
            });

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


var colors = {
  'mh': 'rgba(0, 0, 255, 0.7)',
  'bw': 'rgba(0, 215, 255, 0.7)',

};

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

var vectorSource = new ol.source.Vector();

var igcUrls = [
  'bw.igc',
  'mh.igc',

];

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

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

var time = {
  start: Infinity,
  stop: -Infinity,
  duration: 0
};
vectorSource.on('addfeature', function(event) {
  var 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;
});


var wharton = [-96.1543889, 29.2542778]; // caution partner, read on...
// since we are using OSM, we have to transform the coordinates...
var whartonMercator = ol.proj.fromLonLat(wharton);




var map = new ol.Map({
  layers: [
    new ol.layer.Tile({
      source: new ol.source.OSM()
    }),
    new ol.layer.Vector({
      source: vectorSource,
      style: styleFunction
    }),
    vectorLayer,
    vectorLineLayer
  ],
  target: 'map',
  controls: ol.control.defaults({
    attributionOptions: /** @type {olx.control.AttributionOptions} */ ({
      collapsible: false
    })
  }),
  view: new ol.View({
    center: whartonMercator,
    zoom: 10
  })
});



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

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

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

var imageStyle = new ol.style.Circle({
  radius: 5,
  fill: null,
  stroke: new ol.style.Stroke({
    color: 'rgba(255,0,255,0.9)',
    width: 1
  })
});
var strokeStyle = new ol.style.Stroke({
  color: 'rgba(255,0,255,0.9)',
  width: 1
});
map.on('postcompose', function(evt) {
  var vectorContext = evt.vectorContext;
  if (point !== null) {
    vectorContext.setImageStyle(imageStyle);
    vectorContext.drawPointGeometry(point);
  }
  if (line !== null) {
    vectorContext.setFillStrokeStyle(null, strokeStyle);
    vectorContext.drawLineStringGeometry(line);
  }
});

var featureOverlay = new ol.layer.Vector({
  source: new ol.source.Vector(),
  map: map,
  style: new ol.style.Style({
    image: new ol.style.Circle({
      radius: 5,
      fill: new ol.style.Fill({
        color: 'rgba(255,0,0,0.9)'
      }),
      stroke: null
    })
  })
});

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

</script>
</body>
</html>

Answer 1

您应该更改

var pointFeature = new ol.Feature(wha, {label: "Airport"});

到

var pointFeature = new ol.Feature({geometry: wha, label: "Airport"});

请参见http://openlayers.org/en/latest/apidoc/module-ol_Feature-Feature.html，以了解您对ol.Feature的理解不佳

替换

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

使用

var vectorLayer = new ol.layer.Vector({
    source: vectorSource,
    style: function(feature) {
      console.log('Check you get the property', feature.get('label'));
      style.getText().setText(feature.get('label'));
      return [style];
    }
});

PS1：已通过推荐测试 PS2：我认为return style;就足够了，而我不得不return [style];，在这里我没有很好的解释。根据文档，它应该可以工作，而在其他情况下，它可以工作，例如http://openlayers.org/en/v4.6.5/examples/street-labels.html

OpenLayers-如何显示功能标签？

1 个答案: