[GIS] Limit Zoom on WMTS Layer using Openlayers 2.12

openlayers-2wmts

I'm implementing a baselayer to be used by a Plone addon (collective.geo.openlayers). My implementation specifically creates a layer and returns it to the addon, which enables many different layers to be configured through a webinterface.

I got it working well, but there is one problem I'm facing that I cannot wrap my head around.

The map displayed is a small local map which only shows tiles when zoomed in to zoom level 11 and higher. For this reason I would like to limit the user from zooming out farther than that.

But when I try to add maxZoomLevel, minZoomLevel or numZoomLevels to the layer definition I get type errors in the getTileInfo function because Openlayers is trying to access the longitude of the tileOrigin property which for some reason is null.

I tried different suggestions about limiting the zoom level but to no avail.

Does anyone know how to limit the zoom levels in the following layer definition?

I cannot simply work around the issue by doing something to the map instance itself, as I only control the layer creation.

function() {

var zugmap_matrixids = [{ 
        identifier : 0,
        topLeftCorner : new OpenLayers.LonLat(919690.324327, 5987771.047746)
    }, {
        identifier : 1,
        topLeftCorner : new OpenLayers.LonLat(929474.2639475, 5987771.047746)
    }, {
        identifier : 2,
        topLeftCorner : new OpenLayers.LonLat(929474.2639456, 5987771.04773376)
    }, {
        identifier : 3,
        topLeftCorner : new OpenLayers.LonLat(931920.24885072, 5985325.06282864)
    }, {
        identifier : 4,
        topLeftCorner : new OpenLayers.LonLat(931920.24885072, 5984102.07037608)
    }, {
        identifier : 5,
        topLeftCorner : new OpenLayers.LonLat(932531.745078525, 5983490.57415958)
    }, {
        identifier : 6,
        topLeftCorner : new OpenLayers.LonLat(932837.49319014, 5983184.82603666)
    }, {
        identifier : 7,
        topLeftCorner : new OpenLayers.LonLat(932990.36724671, 5983031.95198009)
    }
]; 

var layer = new OpenLayers.Layer.WMTS({
    name : "LuftbildPlus+",
    url : [
        "http://webdienste.zugmap.ch/OrthofotoPlus_tiled/service.svc/get"
    ],
    layer : "LuftbildPlusGoogle",
    matrixSet : "LuftbildPlusGoogle",
    matrixIds : zugmap_matrixids, 
    tileFullExtent : new OpenLayers.Bounds(919690.324327, 5948635.289264, 978393.96205, 5987771.047746),
    maxExtent : new OpenLayers.Bounds(919690.324327, 5948635.289264, 978393, 5987771),
    style : "default",
    format : "image/png",
    isBaseLayer : true,
    zoomOffset : -11,
    //numZoomLevels: 8
});

return layer
}

You'll notice that numZoomLevels is commented out. I feel like this should be the correct property to set as the matrices only contain 8 levels, but if I uncomment it, I get the type error I was talking about. If I don't use numZoomLevels or any other property that controls the zoom the map works fine.

Best Answer

Here is a link to an example that helped me : http://www.wightpaths.co.uk/ In my case the key was to define the 'resolutions' array with all resolution I let people watch and also I wanted the minimum zoom to be the 7th so I defined 'zoomOffset' at 7.

Look at my code : 

  var ign= new OpenLayers.Layer.WMTS(
  {
    name: "IGN Ortho",
    url: "http://gpp3-wxs.ign.fr/mykey/wmts",
    layer: 'ORTHOIMAGERY.ORTHOPHOTOS',
    style: 'normal',
    matrixSet: "PM",
    format:'image/jpeg',
    resolutions: [1222.9924523925781,611.4962261962891,305.74811309814453,152.87405654907226,76.43702827453613,38.218514137268066,19.109257068634033,9.554628534317017,4.777314267158508,2.388657133579254,1.194328566789627,0.5971642833948135,0.29858214169740677],
    zoomOffset: 7,
    attribution: 'provided by IGN',
    exceptions:"text/xml"
  },
  {
    isBaseLayer: true,
    units: wm.getUnits()
  }
);
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