三章-24-按限定范围加载图层

作者: 彩云飘过 | 来源:发表于2020-04-20 17:51 被阅读0次

三章-24-按限定范围加载图层
openlayers6加载geojson图层的方法
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本文基于腾讯课堂老胡的课《跟我学Openlayers--基础实例详解》做的学习笔记，使用的openlayers 5.3.x api。

源码见 1024.html ，对应的官网示例 https://openlayers.org/en/latest/examples/layer-extent.html?q=setExtent

image.png

<!DOCTYPE html>
<html>

<head>
  <title>按限定范围加载图层
  </title>
  <link rel="stylesheet" href="../include/ol.css" type="text/css">
  <script src="../include/ol.js"></script>
  <script src="../include/jquery-3.1.1.min.js"></script>
</head>
<style>

</style>

<body>
  <div>
    <button type="button" class="btn btn-default" id="India">印度</button>
    <button type="button" class="btn btn-default" id="Argentina">阿根廷</button>
    <button type="button" class="btn btn-default" id="Nigeria">尼日利亚</button>
    <button type="button" class="btn btn-default" id="Sweden">瑞典</button>
    <div id="map" class="map"></div>


    <script>
     
      function transform(extent) {
        return ol.proj.transformExtent(extent, 'EPSG:4326', 'EPSG:3857');
      }

      var extents = {
        India: transform([68.17665, 7.96553, 97.40256, 35.49401]),
        Argentina: transform([-73.41544, -55.25, -53.62835, -21.83231]),
        Nigeria: transform([2.6917, 4.24059, 14.57718, 13.86592]),
        Sweden: transform([11.02737, 55.36174, 23.90338, 69.10625])
      };

      var base = new ol.layer.Tile({
        source: new ol.source.TileJSON({
          url: 'https://api.tiles.mapbox.com/v4/mapbox.world-light.json?secure&access_token=pk.eyJ1IjoiYWhvY2V2YXIiLCJhIjoiY2pzbmg0Nmk5MGF5NzQzbzRnbDNoeHJrbiJ9.7_-_gL8ur7ZtEiNwRfCy7Q',
          crossOrigin: 'anonymous'
        })
      });

      //覆盖图
      var overlay = new ol.layer.Tile({
        extent: extents.India,
        source: new ol.source.TileJSON({
          url: 'https://api.tiles.mapbox.com/v4/mapbox.world-black.json?secure&access_token=pk.eyJ1IjoiYWhvY2V2YXIiLCJhIjoiY2pzbmg0Nmk5MGF5NzQzbzRnbDNoeHJrbiJ9.7_-_gL8ur7ZtEiNwRfCy7Q',
          crossOrigin: 'anonymous'
        })
      });

      var map = new ol.Map({
        layers: [base, overlay],
        target: 'map',
        view: new ol.View({
          center: [0, 0],
          zoom: 1
        })
      });

      //遍历显示限制地图数组，当按钮单击的时候，设置图层TileJSON的边界
      for (var key in extents) {
        document.getElementById(key).onclick = function (event) {
          overlay.setExtent(extents[event.target.id]);
        };
      }
    </script>
</body>

</html>