Question

我想在地图上画一个伦敦的十字架。如果我在地理或web mercator中指定点的坐标，则代码可以工作。但是，如果我在ED50 / UTM区域31N中指定坐标，则它不起作用。根据文档，Point构造函数将空间参考作为最后一个参数。我认为这意味着该点将被转换为地图的坐标系（web mercator）？然而，这一点现在出现在法国中部的某个地方。不确定这里发生了什么？

<!DOCTYPE html>

<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no" />
    <title>London Map</title>
    <link rel="stylesheet" href="https://js.arcgis.com/3.17/esri/css/esri.css">
    <style>
        html, body, #map {
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
    <script src="https://js.arcgis.com/3.17/"></script>
    <script>
      var map;

      require(["esri/map", "esri/geometry/Point", "esri/SpatialReference", "esri/graphic", "dojo/domReady!"], function (Map, Point, SpatialReference, Graphic) {
        map = new Map("map", {
          basemap: "topo",  //For full list of pre-defined basemaps, navigate to http://arcg.is/1JVo6Wd
          center: [0.1, 51.5], // longitude, latitude
          zoom: 8
        });
        map.on("load", function () {
            //var P = new Point({ "x": 0.1, "y": 51.5, "spatialReference": { "wkid": 4326 } });       // geographic: works!
            //var P = new Point({ "x": -10978, "y": 6708911, "spatialReference": { "wkid": 102100 } }); // web mercator: works! 
            //var P = new Point({ "x": 284879, "y": 5711864, "spatialReference": { "wkid": 23031 } }); // somewhere in the middle of France !!??
            var P = new Point([284879, 5711864], new SpatialReference({ wkid: 23031 }));             // somewhere in the middle of France !!??
            var pointSymbol = new esri.symbol.SimpleMarkerSymbol(esri.symbol.SimpleMarkerSymbol.STYLE_X, 10, new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_SOLID, new dojo.Color([0, 0, 0]), 2), new dojo.Color([0, 255, 0, 0.25]));
            var mapPointGraphic = new Graphic(P, pointSymbol);
            map.graphics.add(mapPointGraphic);
        });
      });
    </script>
</head>

<body>
    <div id="map"></div>
</body>
</html>

Answer 1

ESRI JavaScript API，除了WebMercator（102100,102113,3875）和WGS84（4326）之外没有任何客户端投影API。对于这些，它使用esri/geometry/webMercatorUtils模块来转换空间参考。对于所有其他投影系统，您需要使用GeometryService进行投影。下面是相同的示例代码。

require(["dojo/_base/array", "esri/tasks/GeometryService", "esri/tasks/ProjectParameters", "esri/SpatialReference"], function(GeometryService, ProjectParameters, array) {

    var gsvc = new GeometryService("https://utility.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer");

    var P = new Point([284879, 5711864], new SpatialReference({ wkid: 23031 }));
    var outSR = new SpatialReference({wkid:102110});

    var params = new ProjectParameters();
    params.geometries = [P];
    params.outSR = outSR;
    params.transformation = transformation;
    gsvc.project(params, function(projectedGeometries){
        P = projectedGeometries[0];
    });

});

如何在除Web Mercator之外的投影坐标系中向Map添加图形？

1 个答案: