[OpenLayers-Users] Can't restrict Openlayers.Layer.OSM to use specific zoom levels

[Adrian Popa]

Hello,

I have a map that uses just 12 zoom levels by defining numZoomLevels: 12 
and an array of allowed resolutions. All base layers (Google, Yahoo and 
Mapserver) have a similar configuration (e.g. for Google: 
MIN_ZOOM_LEVEL: 7, MAX_ZOOM_LEVEL:19, RESOLUTIONS: res) and work as 
expected.

However, the OSM layer allows me to zoom beyond these resolutions if I 
define it like this:

var osm = new OpenLayers.Layer.OSM.Osmarender('OpenStreetMaps', 
{numZoomLevels: 12, minZoomLevel: 7, maxZoomLevel: 19});

If I add the resolutions parameter something interesting happens: the 
zoom is restricted, but I loose the tiles, because they can no longer be 
found (404 errors):
var osm = new OpenLayers.Layer.OSM.Osmarender('OpenStreetMaps', 
{numZoomLevels: 12, minZoomLevel: 7, maxZoomLevel: 19, resolutions: res});
My "res" array is: var res = [2445.9849046875, 1222.99245234375, 
611.496226171875, 305.7481130859375, 152.87405654296876, 
76.43702827148438, 38.21851413574219, 19.109257067871095, 
9.554628533935547, 4.777314266967774, 2.388657133483887, 
1.1943285667419434, 0.597164283];

The tiles requested have the following URLs: "NetworkError: 404 Not 
Found - http://a.tah.openstreetmap.org/Tiles/tile/1/76/42.png" (this is 
for a zoom level 1, which coresponds to a normal zoom level of 7 (I think))

My question is - is this a bug, or is there a way to instruct the layer 
to "adjust" the value of zoom by a constant (6+x)?

I've looked over the OpenLayers.Layer.OSM definition, and I should be 
able to adjust the url attribute, but I have no idea how to force it to 
do an addition, or if this is the right way to go:

OpenLayers.Layer.OSM = OpenLayers.Class(OpenLayers.Layer.XYZ, {
      name: "OpenStreetMap",
      attribution: "Data CC-By-SA by <a 
href='http://openstreetmap.org/'>OpenStreetMap</a>",
      sphericalMercator: true,
      url: 'http://tile.openstreetmap.org/${z}/${x}/${y}.png',
      CLASS_NAME: "OpenLayers.Layer.OSM"
});

Regards,
Adrian