Question

我是OpenLayers的新手。我正在制作网络地图，但是我不知道为什么geojson图层没有显示，仅显示了基本地图。我的代码如下：

<!DOCTYPE html>
<html>
  <head>
    <title>Flood Plain Risks</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v5.3.0/css/ol.css" type="text/css">
    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<link rel="stylesheet" href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css">
  </head>
  <body>
    <div id="map" class="map"></div>
    <button> <a id="export-png" class="btn btn-default"><i class="fa fa-download"></i> Save Map</a></button>
    <script>
 var map = new ol.Map({
        target: 'map',
        layers: [
          new ol.layer.Tile({
            source: new ol.source.OSM()
          }),
        new ol.layer.Vector({
            title: 'added Layer',
            source: new ol.source.Vector({
            url: 'FLOOD_PLAIN.json',
            format: new ol.format.GeoJSON()
            })
        }),
        new ol.layer.Vector({
            title: 'added Layer',
            source: new ol.source.Vector({
            url: 'BUILDING_FOOTPRINT.json',
            format: new ol.format.GeoJSON()
            })
        })
        ],
        view: new ol.View({
          center: ol.proj.fromLonLat([-80.981948,43.370172]),
          zoom: 14
        })
      });
      document.getElementById('export-png').addEventListener('click', function() {
        map.once('rendercomplete', function(event) {
          var canvas = event.context.canvas;
          if (navigator.msSaveBlob) {
            navigator.msSaveBlob(canvas.msToBlob(), 'map.png');
          } else {
            canvas.toBlob(function(blob) {
              saveAs(blob, 'map.png');
            });
          }
        });
        map.renderSync();
      });
    </script>
  </body>
</html>

GeoJSON数据的投影为NAD83 / UTM区域17N（EPSG：26917）。

它们应该覆盖安大略省的斯特拉特福市。

完整的GeoJSON：

Answer 1

您需要包括自定义投影（NAD83 / UTM区域17N（EPSG：26917））

<script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.4.3/proj4.js"></script>
<script src="https://epsg.io/26917.js"></script>

<script>
ol.proj.proj4.register(proj4);

var dataProjection = ol.proj.get('EPSG:26917');
var map = new ol.Map({
  target: 'map',
  layers: [
    new ol.layer.Tile({
      source: new ol.source.OSM()
    }),
    new ol.layer.Vector({
      title: 'added Layer',
      source: new ol.source.Vector({
        url: 'FLOOD_PLAIN.json.txt',
        format: new ol.format.GeoJSON({
          dataProjection: dataProjection,
          featureProjection: 'EPSG:3857'
        })
      })
    }),
    new ol.layer.Vector({
      title: 'added Layer',
      source: new ol.source.Vector({
        url: 'BUILDING_FOOTPRINT.json.txt',
        format: new ol.format.GeoJSON({
          dataProjection: dataProjection,
          featureProjection: 'EPSG:3857'
        })
      })
    })],
  view: new ol.View({
      center: ol.proj.fromLonLat([-80.981948,43.370172]),
      zoom: 14
  })
});

proof of concept

geojson图层未显示在OpenLayers上

1 个答案: