[gdal-dev] Re: gdal2tiles: tiles in wrong hemisphere, and/or Openlayers problem

[geep999]

Even & Klokan,
1/ Thanks for your comments and link. The light has dawned, and I've now
understood the differences in tile naming between
TMS and XYZ tilsets.

I edited the overlays.html created by gdal2tiles.py to use both
OpenLayers.Layer.TMS and OpenLayers.Layer.XYZ.
Rather than create a 'proper' XYZ tileset, I created a function
xyz_getTileURL to allow OpenLayers.Layer.XYZ 
to read from a TMS tileset.

As it might be of interest for others struggling to understand this stuff, I
attach it below.
Or look at the source on:
http://pgg999.freehostingcloud.com/tiles4_srtm/openlayers.xyz.html

xyz_getTileURL is just a modification of the existing osm_getTileURL &
overlay_getTileURL, 
with Klokan's formula y = (2^z - 1) - y used to convert the TMS Y to the XYZ
Y

2/ I noted that overlays.html calls:
http://www.openlayers.org/api/2.7/OpenLayers.js
This doesn't seem to support Openlayers.Layer.XYZ
Maybe a future version of gdaltiles.py could instead reference a newer
version of Openlayers.
e.g. http://www.openlayers.org/api/2.11/OpenLayers.js


Cheers,
Peter

                    // create XYZ Overlay layer
                    // This is an exercise for me to use Openlayers.Layer.XYZ, 
and write
my own getURL function.
                    // (The TMS tileset was created by gdal2tiles.py. 
                    //  So need to convert from the TMS URL to XYZ URL with
xyz_getTileURL) 
                    // Using a ZXY tileset then "getURL: xyz_getTileURL" is not 
needed and
                    //  the URL would be simply
"http://pgg999.freehostingcloud.com/tiles4_srtm/${z}/${x}/${y}.png";
                    var tiles4_srtm = new 
OpenLayers.Layer.XYZ("OpenLayers.Layer.XYZ",
                        "http://pgg999.freehostingcloud.com/tiles4_srtm/";,
                        { type: 'png', getURL: xyz_getTileURL, alpha: true, 
isBaseLayer: false
});


                //This function allows a TMS tileset to be used with 
OpenLayers.Layer.XYZ
                function xyz_getTileURL(bounds) {
                    var res = this.map.getResolution();
                    var x = Math.round((bounds.left - this.maxExtent.left) / 
(res *
this.tileSize.w));
                    var y = Math.round((this.maxExtent.top - bounds.top) / (res 
*
this.tileSize.h));
                    var z = this.map.getZoom();
                    var limit = Math.pow(2, z);

                        if (mapBounds.intersectsBounds( bounds ) && z >= 
mapMinZoom && z
<= mapMaxZoom ) {
                          x = ((x % limit) + limit) % limit;
                          y = Math.pow(2,z) - y - 1;
                          return this.url + z + "/" + x + "/" + y + "." + 
this.type;
                        } else {
                          return "http://www.maptiler.org/img/none.png";;
                        }

                }


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