SharpGIS博客翻译2006年9月：在local live地图上叠加自己的数据

Overlaying Local Live maps with your own map-data [原文] [翻译] [作者：心帆]

原文：

Recently the Virtual Earth team released a new version of their API . One of the new features allowed to overlay the maps with tiles from your own tile-server. The tile-server can be added using a few lines of javascript like this:

var tileSourceSpec = new VETileSourceSpecification();
tileSourceSpec.ID = "POPDENS" ;
tileSourceSpec.GetTilePath = GetTilePath;
tileSourceSpec.NumServers = 1;
tileSourceSpec.MinZoom = 1;
tileSourceSpec.MaxZoom = 16;
vemap.AddTileSource(tileSourceSpec);
var tileLayer = new VELayerSpecification(VELayerType.VETileSource,"POPDENS", "POPDENS");
tileLayer.Opacity=0.6;
vemap.AddLayer(tileLayer);

This will add a new tile layer named "POPDENS" to the virtual earth map, and make it slightly transparent. The GetTilePath parameter refers to the JavaScript method that creates the request-url to the server. Ex:

function GetTilePath (tileContext) {
if (tileContext != null && tileContext != "undefined" ) {
return "VEmap.ashx?WIDTH=256&HEIGHT=256&X=" + tileContext.XPos + "&Y=" + tileContext.YPos + "&ZoomLevel=" + tileContext.ZoomLevel;
}
}

The X, Y and ZoomLevel parameters in this querystring are unfortunately not simple coordinates, but are the row/column of the tile at the current zoom level. Rob Blackwell has earlier posted an article on how to convert these to longitude/latitude values.

The next step is to create the tile-server. I used SharpMap for this. SharpMap's on-the-fly transformation capability is needed to transform the data to the Mercator projection that Virtual Earth uses, but any map-renderer that can project data could be used. You could also create a javascript that makes the GetTilePath method return a WMS request instead and then use any of the many WMS servers available.

The basic trick is to use Rob Blackwell's methods for calculating the longitude/latitude of each tile's corners, transform these coordinates to the Mercator projection and render the resulting extent.

You can view a small demo of a Population Density map overlaying the Virtual Earth map here: http://showcase.sharpgis.net/ve/
...or you can download the full source: VirtualEarth.zip (389,09 KB)
You can easily add your own data by editing the CreateMap method in /App_Code/Map.cs







译文：

最近Virtual Earth项目组发布了新版本的API . 有一个新特性就是可以在你的tile-server上叠加地图。参照使用以下javascript代码：

var tileSourceSpec = new VETileSourceSpecification();
tileSourceSpec.ID = "POPDENS" ;
tileSourceSpec.GetTilePath = GetTilePath;
tileSourceSpec.NumServers = 1;
tileSourceSpec.MinZoom = 1;
tileSourceSpec.MaxZoom = 16;
vemap.AddTileSource(tileSourceSpec);
var tileLayer = new VELayerSpecification(VELayerType.VETileSource,"POPDENS", "POPDENS");
tileLayer.Opacity=0.6;
vemap.AddLayer(tileLayer);

以上将添加一个新的名称为"POPDENS"图层到virtual earth 地图，并使它有透明的效果。GetFilePath参数是JavaScript的方法，用来创建的服务器URL，例如：

function GetTilePath (tileContext) {
if (tileContext != null && tileContext != "undefined" ) {
return "VEmap.ashx?WIDTH=256&HEIGHT=256&X=" + tileContext.XPos + "&Y=" + tileContext.YPos + "&ZoomLevel=" + tileContext.ZoomLevel;
}
}

在这个请求中，X, Y 和 ZoomLevel参数不是简单的坐标，而是当然缩放比例下tile的行/列值。 Rob Blackwell 早些时候 有一篇文章 讲述如何将它们转换成经纬度值。

下一步是创建tile-server。我使用 SharpMap 。Virtual Earth使用的是 Mercator（麦卡托）投影， SharpMap可以使用任何投影的数据，但必须转化为Mercator投影才能够创建tile-server。你也可以写一个javascript的GetTilePath函数返回一个WMS请求，这样可以使用许多WMS服务器的数据。

The basic trick is to use Rob Blackwell's methods for calculating the longitude/latitude of each tile's corners, transform these coordinates to the Mercator projection and render the resulting extent.

最基本的技巧是需要使用Rob Blackwell的方法来计算每一个tile四个角上的经纬度，将这些坐标转化为Mercator坐标然后这个范围内的地图。

下面是一个简单的将人口密度图叠加到Virtual Earth 上的示例： http://showcase.sharpgis.net/ve/

源码: VirtualEarth.zip (389,09 KB)

修改/App_Code/Map.cs文件中的CreateMap函数，可以很容易的加入自己的数据。



译注：

tile：原意是瓦片, 瓷砖，此文中应该是指整个地图是由一块一块拼起来的，tile指其中的一块。

tile-sever：应该是指能提供由块状地图拼接地图的服务器，例如google maps等等。

不知道以上理解是否正确，更不知道如何翻译成中文。