javascript OpenLayers：自动将 EPSG 4326 -Coordinates 从文本图层转换为地图投影 (EPSG:900913)
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OpenLayers: Automatically transform EPSG 4326 -Coordinates from Text Layer into map`s projection (EPSG:900913)
提问by Ronny
currently, I`m implementing a map App with Mono4Droid and there I`m using a WebView to present a map which is provided by my own tileserver. I`m using OpenLayers to show this map and now I want to use a Text Layer to show some custom POI`s. Unfortunately, the map uses 90013 projection:
目前，我正在使用 Mono4Droid 实现地图应用程序，并在那里使用 WebView 来呈现由我自己的 tileserver 提供的地图。我正在使用 OpenLayers 来显示此地图，现在我想使用文本层来显示一些自定义 POI。不幸的是，地图使用了 90013 投影：
map = new OpenLayers.Map ("map", {
controls:[
new OpenLayers.Control.Navigation(),
new OpenLayers.Control.PanZoomBar(),
new OpenLayers.Control.Permalink(),
new OpenLayers.Control.ScaleLine({geodesic: true}),
new OpenLayers.Control.Permalink('permalink'),
new OpenLayers.Control.MousePosition(),
new OpenLayers.Control.Attribution()],
//maxExtent: new OpenLayers.Bounds(-20037508.34,-20037508.34,20037508.34,20037508.34),
maxResolution: 156543.0339,
numZoomLevels: 19,
units: 'm',
projection: new OpenLayers.Projection("EPSG:900913"),
displayProjection: new OpenLayers.Projection("EPSG:900913")
} );
So when I want to display the Markes provided by the TextLayer, I have to use coordinates in the right format. To center the map is easy:
所以当我想显示 TextLayer 提供的 Markes 时，我必须使用正确格式的坐标。使地图居中很容易：
var lonLat = new OpenLayers.LonLat(lon, lat).transform(new OpenLayers.Projection("EPSG:4326"), map.getProjectionObject());
map.setCenter (lonLat, zoom);
But how can I do this transformation automatically for the TextLayer? I want to have the lat lon values according to the well-known EPSG4326 into the Text Layer data file (columns lat long) and not the values according to 900913 (what I`m doing at the moment to have it work).
但是如何为 TextLayer 自动执行此转换？我想将根据众所周知的 EPSG4326 的经纬度值放入文本层数据文件（经纬度列）中，而不是根据 900913 的值（我目前正在做的工作）。
Is there a way to let OpenLayers transform the Text Layer`s coordinates automatically to the format used in the map? Maybe a callback function to override like onShow?
有没有办法让 OpenLayers 将文本图层的坐标自动转换为地图中使用的格式？也许是一个回调函数来覆盖像 onShow？
Thanks for your help! Otherwise I would have to translate the lat lon values myself and put the calculated value in the text file which will make performance to suffer...
谢谢你的帮助！否则我将不得不自己翻译经纬度值并将计算出的值放在文本文件中，这会使性能受到影响......
回答by Ronny
Finally, I found the answer myself and I must say I`m very impressed! OpenLayers is quite powerful! Here is my solution: In the options of the map-object you have to set displayOptions to the projection of your layer, in my case it`s the following to support EPSG:4326:
最后，我自己找到了答案，我必须说我印象非常深刻！OpenLayers 非常强大！这是我的解决方案：在地图对象的选项中，您必须将 displayOptions 设置为图层的投影，在我的情况下，以下内容支持 EPSG:4326：
displayProjection: new OpenLayers.Projection("EPSG:4326")
Then you only have to take care that the layer uses this projection (if it`s not the default value already). In my case, Text Layer didn`t work correctly on Android (in a WebView): I couldn`t open a popup when clicking on the image of a marker from the textfile. Instead, I`m using a Vector-Layer according to the sundials-Example:
然后你只需要注意图层使用这个投影（如果它不是默认值）。就我而言，文本层在 Android 上无法正常工作（在 WebView 中）：单击文本文件中的标记图像时，我无法打开弹出窗口。相反，我根据日晷示例使用矢量层：
new OpenLayers.Layer.Vector("TextLayer", {
projection: map.displayProjection,
strategies: [new OpenLayers.Strategy.Fixed()],
protocol: new OpenLayers.Protocol.HTTP({
url: "layerdata/chargingstationsmaptxtlayer.txt",
format: new OpenLayers.Format.Text({
extractStyles: true,
extractAttributes: true
})
})
});
In the text-file I can now use the LatLon-values of the EPSG-4326 format. It`s so easy ;-)
在文本文件中，我现在可以使用 EPSG-4326 格式的 LatLon 值。太简单了 ;-)
