【问题标题】:OpenLayers: Map doesn't render with a non 'standard' EPSG-codeOpenLayers:地图不使用非“标准”EPSG 代码渲染
【发布时间】:2019-07-25 12:07:51
【问题描述】:

我在使用 EPSG 3031 中的地图时遇到问题。

根据我的研究,我已经了解到投影的参数必须在 javascript 文件中定义,因此 epsg.io 在我的脚本中可以正常工作。

但是当我在新创建的视图和转换后的中心中使用实际的 EPSG:3031 时,地图不会呈现。 它工作的唯一方法是选择 EPSG:4326 或 3857 与中心 [0,0] 实际上没有任何意义。

我的 javascript 看起来像这样:

// register EPSG
proj4.defs("EPSG:3031","+proj=stere +lat_0=-90 +lat_ts=-71 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs");

//set projection
var proj3031=ol.proj.get('EPSG:3031');

//test if coordinate transformation is properly working

var center2 = ol.proj.transform([0, -80], 'EPSG:4326', 'EPSG:3031');
;

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

var esriArctic = new ol.layer.Tile({
	title : 'ESRI Imagery',
	type : 'base',
	zIndex: 0,				
	source : new ol.source.XYZ({
		attributions : [new ol.Attribution({
			html : 'Tiles &copy; <a href="http://services.arcgisonline.com/ArcGIS/rest/services/Polar/Antarctic_Imagery/MapServer">ArcGIS</a>'
		})],
		url : 'https://server.arcgisonline.com/ArcGIS/rest/services/Polar/Antarctic_Imagery/MapServer/tile/{z}/{y}/{x}',
		wrapX: false,
	})
});
var map = new ol.Map({
  target: 'map',
  layers: [ esriArctic],
  //layers: [ baseMapLayer],
  view: new ol.View({
	  //projection: "EPSG:4326",
	  projection: proj3031,
    //center: [0,0],
    center: center2, 
    zoom: 5 //Initial Zoom Level
        })
});

我的 html 看起来像这样:

<!DOCTYPE html> 
<style type="text/css">
  #map{
   width:100%;
   height:600px;
  }
 </style>
 <!--Basic styling for map div, 
 if height is not defined the div will show up with 0 px height  -->

</head>
<script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.4.3/proj4.js"></script>
<script src="http://epsg.io/3031.js"></script>

<body>
 <div id="map">
  <!-- Your map will be shown inside this div-->
 </div>
</body>
<script src="https://openlayers.org/en/v4.6.5/build/ol.js" type="text/javascript"></script>
 <script type="text/javascript" src="map.js" type="text/javascript"></script>
 <!-- Our map file -->

</html>>
 <!-- Openlayesr JS fIle -->

我怎样才能让它工作,为什么它现在不能工作?

【问题讨论】:

    标签: javascript openlayers projection epsg


    【解决方案1】:

    非全局投影中的 Arcgis 源具有非标准切片网格。如果可以添加正确的 tilegrid,@RalphL 的方法将起作用,但可以通过将其定义为 TileArcGISRest 源来自动完成。如果您想使用 OSM 作为基础层重投影,例如 EPSG:3857,它无法到达极坐标的两极,会导致 OpenLayers 无法处理并崩溃的错误。我通过定义转换函数来解决这个问题,这些转换函数通过中间投影让代码捕获任何错误。

    function reprojectionErrorHandler(projections, opt_intermediate) {
    
      var intermediate = opt_intermediate || 'EPSG:4269';
    
      function transform(projA, projB) {
    
        return function (input, opt_output, opt_dimension) {
            var length = input.length;
            var dimension = opt_dimension !== undefined ? opt_dimension : 2;
            var output = opt_output !== undefined ? opt_output : new Array(length);
            var ll, point, i, j;
            try {
                for (i = 0; i < length; i += dimension) {
                    ll = ol.proj.transform([input[i], input[i + 1]], projA, intermediate);
                    point = ol.proj.transform([ll[i], ll[i + 1]], intermediate, projB);
                    output[i] = point[0];
                    output[i + 1] = point[1];
                    for (j = dimension - 1; j >= 2; --j) {
                        output[i + j] = input[i + j];
                    }
                }
            } catch (e) {}
            return output;
        };
    
      }
    
      if (Array.isArray(projections)) {
        for (i = 0; i < projections.length-1; i++) {
            for (j = i+1; j < projections.length; j++) {
                if (ol.proj.get(projections[i]).getCode() != ol.proj.get(projections[j]).getCode() &&
                    ol.proj.get(projections[i]).getCode() != ol.proj.get(intermediate).getCode() &&
                    ol.proj.get(projections[j]).getCode() != ol.proj.get(intermediate).getCode() ) {
    
                    ol.proj.addCoordinateTransforms(
                        projections[i],
                        projections[j],
                        transform(projections[i], projections[j]),
                        transform(projections[j], projections[i])
                    );
    
                    ol.proj.addCoordinateTransforms(
                        projections[j],
                        projections[i],
                        transform(projections[j], projections[i]),
                        transform(projections[i], projections[j])
                    );
    
                }
            }
        }
      }
    
    }
    
    proj4.defs("EPSG:3031", "+proj=stere +lat_0=-90 +lat_ts=-71 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs");
    ol.proj.proj4.register(proj4);
    var proj3031 = ol.proj.get('EPSG:3031');
    
    reprojectionErrorHandler(['EPSG:3031', 'EPSG:3857'])
    
    var baseMapLayer = new ol.layer.Tile({
      source: new ol.source.OSM()
    });
    
    var esriArctic = new ol.layer.Tile({
      title: 'ESRI Imagery',
      type: 'base',
      zIndex: 0,
      opacity: 0.5,
      source: new ol.source.TileArcGISRest({
        url: 'https://services.arcgisonline.com/arcgis/rest/services/Polar/Antarctic_Imagery/MapServer'
      })
    });
    
    var map = new ol.Map({
      target: 'map',
      layers: [baseMapLayer, esriArctic],
      view: new ol.View({
        projection: proj3031,
        center: ol.proj.fromLonLat([0, -80], proj3031),
        zoom: 3
      })
    })
       html,
       body,
       #map {
         width: 100%;
         height: 100%;
         overflow: hidden;
       }
    <script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.5.0/proj4.js"></script>
    <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>
    <body>
      <div id="map" class="map"></div>
    </body>

    这是@RalphL 的方法以正确的位置为中心,使用基于此处列出的完整范围和最大分辨率的 tilegrid https://services.arcgisonline.com/arcgis/rest/services/Polar/Antarctic_Imagery/MapServer 与普通 EPSG:3857 tilegrid 不同的是,tile 不完全适合范围

    proj4.defs("EPSG:3031", "+proj=stere +lat_0=-90 +lat_ts=-71 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs");
    ol.proj.proj4.register(proj4);
    var proj3031 = ol.proj.get('EPSG:3031');
    
    var extent = [-3.369955099203E7, -3.369955099203E7, 3.369955099203E7, 3.369955099203E7];
    var maxResolution = 238810.81335399998;
    
    var resolutions = [];
    for (var i = 0; i < 24; i++) {
      resolutions[i] = maxResolution / Math.pow(2, i);
    }
    
    var esriArctic = new ol.layer.Tile({
      title: 'ESRI Imagery',
      type: 'base',
      zIndex: 0,
      source: new ol.source.XYZ({
        url: 'https://services.arcgisonline.com/arcgis/rest/services/Polar/Antarctic_Imagery/MapServer/tile/{z}/{y}/{x}',
        projection: proj3031,
        tileGrid: new ol.tilegrid.TileGrid({ extent: extent, resolutions: resolutions }),
      })
    });
    
    var map = new ol.Map({
      target: 'map',
      layers: [esriArctic],
      view: new ol.View({
        projection: proj3031,
        center: ol.proj.fromLonLat([0, -80], proj3031),
        zoom: 3
      })
    })
       html,
       body,
       #map {
         width: 100%;
         height: 100%;
         overflow: hidden;
       }
    <script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.5.0/proj4.js"></script>
    <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>
    <body>
      <div id="map" class="map"></div>
    </body>

    重投影中极点处的白洞主要是透明的,快速解决方法是在 css 中设置地图 div 背景以匹配冰,例如

       .map {
         background-color: #e7e9f6;
       }
    

    但是,仍然可以看到薄薄的白色边缘。

    基于层 spy 示例https://openlayers.org/en/v4.6.5/examples/layer-spy.html 的更好解决方案可能是从南极层中裁剪出真正的非透明白色环绕

    function reprojectionErrorHandler(projections, opt_intermediate) {
    
      var intermediate = opt_intermediate || 'EPSG:4269';
    
      function transform(projA, projB) {
    
        return function (input, opt_output, opt_dimension) {
            var length = input.length;
            var dimension = opt_dimension !== undefined ? opt_dimension : 2;
            var output = opt_output !== undefined ? opt_output : new Array(length);
            var ll, point, i, j;
            try {
                for (i = 0; i < length; i += dimension) {
                    ll = ol.proj.transform([input[i], input[i + 1]], projA, intermediate);
                    point = ol.proj.transform([ll[i], ll[i + 1]], intermediate, projB);
                    output[i] = point[0];
                    output[i + 1] = point[1];
                    for (j = dimension - 1; j >= 2; --j) {
                        output[i + j] = input[i + j];
                    }
                }
            } catch (e) {}
            return output;
        };
    
      }
    
      if (Array.isArray(projections)) {
        for (i = 0; i < projections.length-1; i++) {
            for (j = i+1; j < projections.length; j++) {
                if (ol.proj.get(projections[i]).getCode() != ol.proj.get(projections[j]).getCode() &&
                    ol.proj.get(projections[i]).getCode() != ol.proj.get(intermediate).getCode() &&
                    ol.proj.get(projections[j]).getCode() != ol.proj.get(intermediate).getCode() ) {
    
                    ol.proj.addCoordinateTransforms(
                        projections[i],
                        projections[j],
                        transform(projections[i], projections[j]),
                        transform(projections[j], projections[i])
                    );
    
                    ol.proj.addCoordinateTransforms(
                        projections[j],
                        projections[i],
                        transform(projections[j], projections[i]),
                        transform(projections[i], projections[j])
                    );
    
                }
            }
        }
      }
    
    }
    
    proj4.defs("EPSG:3031", "+proj=stere +lat_0=-90 +lat_ts=-71 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs");
    ol.proj.proj4.register(proj4);
    var proj3031 = ol.proj.get('EPSG:3031');
    
    reprojectionErrorHandler(['EPSG:3031', 'EPSG:3857'])
    
    var baseMapLayer = new ol.layer.Tile({
      source: new ol.source.XYZ({
        url: 'https://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}',
        maxZoom: 23
      })
    });
    
    var extent = [-3.369955099203E7, -3.369955099203E7, 3.369955099203E7, 3.369955099203E7];
    var maxResolution = 238810.81335399998;
    
    var resolutions = [];
    for (var i = 0; i < 24; i++) {
      resolutions[i] = maxResolution / Math.pow(2, i);
    }
    
    var esriArctic = new ol.layer.Tile({
      title: 'ESRI Imagery',
      type: 'base',
      zIndex: 0,
      source: new ol.source.XYZ({
        url: 'https://services.arcgisonline.com/arcgis/rest/services/Polar/Antarctic_Imagery/MapServer/tile/{z}/{y}/{x}',
        projection: proj3031,
        tileGrid: new ol.tilegrid.TileGrid({ extent: extent, resolutions: resolutions }),
      })
    });
    
    esriArctic.on('precompose', function(event) {
      radius = 4000000 / event.frameState.viewState.resolution;
      var ctx = event.context;
      var pixelRatio = event.frameState.pixelRatio;
      ctx.save();
      ctx.beginPath();
      position = map.getPixelFromCoordinate(ol.proj.transform([0, -90], 'EPSG:4326', 'EPSG:3031'));
      // only show a circle around the position
      ctx.arc(position[0] * pixelRatio, position[1] * pixelRatio, radius * pixelRatio, 0, 2 * Math.PI);
      ctx.clip();
    });
    
    // after rendering the layer, restore the canvas context
    esriArctic.on('postcompose', function(event) {
      var ctx = event.context;
      ctx.restore();
    });
    
    var map = new ol.Map({
      target: 'map',
      layers: [baseMapLayer, esriArctic],
      view: new ol.View({
        projection: proj3031,
        center: ol.proj.fromLonLat([0, -80], proj3031),
        zoom: 3
      })
    })
       html,
       body,
       #map {
         width: 100%;
         height: 100%;
         overflow: hidden;
       }
    <script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.5.0/proj4.js"></script>
    <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>
    <body>
      <div id="map" class="map"></div>
    </body>

    【讨论】:

    • 非常感谢,sn-ps 分别解决了我的问题!但是我有一个关于覆盖基础层的第一个解决方案的问题:我用完全适合南极地图的 ArcGIS World Imagery 替换了 OSM。不幸的是,就像在 OSM 中一样,极点周围的最后一个度数显示为白色,因为我猜那里没有定义投影。有什么办法不显示白色圆圈?
    • 最好的方法是从南极地图上剪下白色的环绕。我添加了另一个 sn-p。
    • 效果很好!非常感谢:)
    【解决方案2】:

    请看下面的sn-p:

    proj4.defs("EPSG:3031", "+proj=stere +lat_0=-90 +lat_ts=-71 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs");
    ol.proj.proj4.register(proj4);
    var proj3031 = ol.proj.get('EPSG:3031');
    
    var esriArctic = new ol.layer.Tile({
      title: 'ESRI Imagery',
      type: 'base',
      zIndex: 0,
      source: new ol.source.XYZ({
        url: 'https://services.arcgisonline.com/arcgis/rest/services/Polar/Antarctic_Imagery/MapServer/tile/{z}/{y}/{x}'
      })
    });
    
    var map = new ol.Map({
      target: 'map',
      layers: [esriArctic],
      view: new ol.View({
        center: ol.proj.fromLonLat([0, -80], proj3031),
        zoom: 3
      })
    })
       html,
       body,
       #map {
         width: 100%;
         height: 100%;
         overflow: hidden;
       }
    <script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.5.0/proj4.js"></script>
    <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>
    <body>
      <div id="map" class="map"></div>
    </body>

    【讨论】:

    • [0, -80] 位于南极大陆上,地图设置为以该位置为中心,但非 3857 来源不使用标准瓦片网格,因此瓦片在地图上放错了位置中心出现偏离目标
    • 感谢您帮助卡片使用此选项进行渲染,但正如 Mike 已经建议的那样,坐标仍然放错了位置。我试图用中心标记南极点:ol.proj.fromLonLat([0, -90], proj3031),它显然不合适
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