[OpenLayers-Users] OpenLayers Question: Google Physical Projections and epsg:26915

Fri Jun 27 08:43:31 EDT 2008

You can't change the projection of the Google layer - it comes in one  
projection, spherical mercator.  If you want to overlay your data on  
the Google base data, you have to serve it up in a spherical mercator  
projection.  There is an ad-hoc EPSG code for this, EPSG:900913 and  
you can find the actual projection parameters at:

http://spatialreference.org/ref/user/google-mapsmicrosoft-live/

I believe that there is now a real EPSG code for this projection in  
the latest EPSG release but I am not sure how widely supported it is  
yet.

I would suggest starting with the spherical mercator examples.

Cheers

Paul

On 27-Jun-08, at 1:16 AM, Matthew Pettis wrote:

> Hi List,
>
> I'm trying to put 2 baselayers in my OpenLayers web object.  One  
> layer is my political map of Minnesota, which has data in epsg: 
> 26915.  The other object I want to use is a Google Maps street view  
> layer.  What I am having trouble doing is making them agree on the  
> projection and having Google Maps use that projection to render it's  
> layer.  I thought the code below (at end of email) should work, but  
> I am obviously missing something.
>
> If I use the ol_ms layer with the map object without the gmap layer,  
> it renders fine.  If I use the gmap layer by itself, and define map  
> like:
>
>             map = new OpenLayers.Map('map');
>
> that is, same as the first one but with no configuration  
> information, that too works fine.
>
> However, putting them as base layers on the same map as laid out  
> below doesn't work.  When I switch to the google map, I get some  
> gray rectangle and the standard google branding stuff at the bottom,  
> but no real map.  I would like it so the same bounds that were being  
> used for the mapserver map were used.
>
> I suspect it is a projection thing that I am not understanding that  
> is in the way.  I note that the Bounds object I use for the  
> mapserver map has bounds like:
>
> new OpenLayers.Bounds(184056.505,4809728.25,767381.245,5478975.75)
>
> which is obviously in meters.  But when I dump out the bounds for  
> the working google map by itself, the 4 numbers are in latlon  
> (-180,-90,180,90).  I suspect it is trying to read the epsg:26915  
> bounds, which are in meters, as latlon bounds, and making the  
> display with the map as some orders of magnitude large scale map  
> that has the entire world mapped to a pixel on my screen.
>
> Question: how do I make Google realize that the map is in epsg:26915  
> and give me its map in commensurate units?  I thought that by  
> defining the projection of the map with epsg:26915, that when I  
> added the google layer to the map that it would know to project  
> itself correctly.  Do I have to somehow manually coerce these  
> things, and if so, how?
>
> Thanks for your time and help,
> Matt
>
>
> = 
> = 
> ======================================================================
> <html xmlns="http://www.w3.org/1999/xhtml">
>   <head>
>     <title>OpenLayers Example</title>
> <!--    <script src="http://www.openlayers.org/api/OpenLayers.js"></ 
> script> -->
>     <script src="http://localhost/_common//OpenLayers-2.6/OpenLayers.js 
> "></script>
>     <script src="http://maps.google.com/maps?file=api&amp;v=2&amp;key=ABQIAAAAytPEybOjkPfSINF9aqMnSRRV_Z48x51l4m6KiJWs2Yue7BruuxS9q420SXqAbRhYk8GzmgwCugf2Fw 
> "
>       type="text/javascript"></script>
>     <script type="text/javascript">
>         var map = null;
>         function init(){
>
>             map = new OpenLayers.Map(
>                 'map',
>                 {
>                       maxResolution: 'auto'
>                     , maxExtent: new  
> OpenLayers.Bounds(184056.505,4809728.25,767381.245,5478975.75)
>                     , units: 'm'
>                     , projection: "EPSG:26915"
>                 }
>             );
>
>             var ol_ms = new OpenLayers.Layer.MapServer(
>                 "Mapserver Untiled"
>                 , "http://localhost/cgi-bin/mapserv.exe?map=C:\\ms4w\ 
> \Apache\\htdocs\\ol\\map.map"
>                 , {layers: 'state'}
>                 , {singleTile: true}
>             );
>             map.addLayer(ol_ms);
>
>             var gmap = new OpenLayers.Layer.Google("Google Streets");
>             map.addLayer(gmap);
>
>             map.zoomToMaxExtent();
>             map.addControl(new OpenLayers.Control.LayerSwitcher());
>
>         }
>     </script>
>   </head>
>
>   <body onload="init()">
>     <div id="map" class="smallmap" style="width:400;height:300"></div>
>   </body>
>
> </html>
> = 
> = 
> ======================================================================
>
> -- 
> It is from the wellspring of our despair and the places that we are  
> broken that we come to repair the world.
> -- Murray Waas _______________________________________________
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