[OpenLayers-Dev] Difficulties while using TileCache with exotic projection (EPSG:32188) with a WMS layer.

Mon Jun 18 13:03:12 EDT 2007

Hello everybody !

I'm trying to use OpenLayers on my own WMS Server. At the beginning, I
was using OpenLayers without any TileCache.
Everything was works quite well. Here you can see what was the result:

http://demo3.kheops-tech.com:8080/site_jmap/montreal.html

and here is a sample of source code:

    <script type="text/javascript">
        <!--
        function init(){
			var minx = 264875.53709076217;
			var miny = 5028255.887191531;;
			var maxx = 311635.1585273513;
			var maxy = 5065756.947977615;

			var map = new OpenLayers.Map( $('map'),
			{maxExtent: new OpenLayers.Bounds(minx,miny,maxx,maxy),
			maxResolution: "auto", projection: "EPSG:32188"});

			map.addLayers(
			[new OpenLayers.Layer.WMS(
				"Montreal","../mtlwms/wms?",
				{layers: "", format: "image/gif"},
				{isBaseLayer: "true", maxResolution: 'auto'})
			]);

			map.addControl(new OpenLayers.Control.LayerSwitcher());

			map.zoomToMaxExtent();
        }
        // -->
    </script>

As you can see, I was using a different projection than default, I was
with EPSG:32188.

Then we decided to use TileCache for improving the first version.
Because we were using a TomCat server; we started by using
TileCacheAsJavaServlet.
This is a Servlet implementation of TileCache 1.4 with jython.
TileCache is unchanged.

With is downloadable here:
http://www.resc.rdg.ac.uk/twiki/bin/view/Resc/TileCacheAsJavaServlet

We first installed it and tried with a WMS showing world map from our
WMS server. After a few fixes of our WMS implementation on our server,
this works well. So our WMS server is compatible with TileCache.

Next, I tried to use TileCache with the first layer that I used
before, here I had my first problems.

My first mistake was to not specify bbox on my tilecache.cfg and also
to not specify maxExtend and maxResolution for my Openlayers html file
'index.html'

	[montreal]
	type=WMSLayer
	url=http://demo3.kheops-tech.com:8080/mtlwms/wms?
	extension=png
	srs=EPSG:32188
	layers=Topographie

  <script defer="defer" type="text/javascript">
	var map = new OpenLayers.Map( $('map'),
	{projection: "EPSG:32188"});
    var wms = new OpenLayers.Layer.WMS( "JMAP WMS",
        "http://localhost:8080/TileCache", {layers: 'montreal',
format: "image/png"});
    map.addLayer(wms);
    map.zoomToMaxExtent();
  </script>

Here TileCache worked well, it loads Tiles from my WMS Server, but
they were white because they were not on place were we can see datas.
You can try this code, the WMS server is online ;)

So my next try is about specifing bbs on tilecache.cfg and
maxResolution and maxExtend on index.html

Now I have

[montreal]
type=WMSLayer
url=http://demo3.kheops-tech.com:8080/mtlwms/wms?
extension=png
bbox=264875.54,5028255.89,311635.16,5065756.95
srs=EPSG:32188
layers=Topographie

Here I have questions, are the bbox values in the same unit as my
projection ? That is to say EPSG:32188 ?

And I have as index.html ->

	<html>
	<head>
	    <script src="OpenLayers-2.3.js"></script>
	</head>
	<body>
	  <div style="width:100%; height:100%" id="map"></div>
	  <script defer="defer" type="text/javascript">

		var min_x = 264875.54;
		var min_y = 5028255.89;
		var max_x = 311635.16;
		var max_y = 5065756.95;

		var map = new OpenLayers.Map( $('map'),
		{maxExtent: new OpenLayers.Bounds(min_x,min_y,max_x,max_y),
maxResolution: 91.327 ,projection: "EPSG:32188"});
	    var wms = new OpenLayers.Layer.WMS( "wms",
	        "http://localhost:8080/TileCache", {layers: 'montreal',
format: "image/png"});
	    map.addLayer(wms);
		if (!map.getCenter()) map.zoomToMaxExtent();
	  </script>
	</body>
	</html>

 When I'm tring to see a Tile i've got error at:
 http://localhost:8080/TileCache/?LAYERS=montreal&FORMAT=image%2Fpng&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&SRS=EPSG%3A32188&BBOX=276565.396%2C5051635.602%2C288255.252%2C5063325.458&WIDTH=256&HEIGHT=256

 Exception: couldn't calculate tile index for layer montreal from
([276565.396, 5051635.602, 288255.252, 5063325.458])

 I don't understand there are not the values that I specified :(

 I have got also a question about the maxResolution we told me on IRC
that it is in map unit/pixel. So I calculate my maxResolution like
this:

 (max_x - min_x) / ( 2 * each_tile_size) =
 (311635.16 - 264875.54) / (2 * 256)

 This means, I think, map is shown in two tiles. The bounds where
found from the BoundingBox element from the GetCapabilities XML File.

You can check this XML file from:
http://demo3.kheops-tech.com:8080/mtlwms/wms?SERVICE=WMS&VERSION=1.3.0&request=GetCapabilities

My aim is just to use our WMS Layer with TileCache.

Thanks a lot for your help,

Kevin Emamirad