Load layers only when zoom level is reached

Question

I'm trying to load different layers based on the user zoom level with OpenLayers. I've seen some similar questions in here, but they load the layer and then hide/show it based on the zoom level.

I don't want the layer to be loaded. I've managed to use some answers and came with a solution, but I don't like it that much. There must be an easier way. Can anybody point me in the right direction?

Here is the solution I've found so far.

map.events.on({ "zoomend": function (e) {
        if (this.getZoom() > 8) {
            // Setup single tiled layer
            var untiled = new OpenLayers.Layer.WMS("cite:ly_parc - Untiled", "http://localhost:8082/geoserver/cite/wms", 
                {
                    LAYERS: 'cite:ly_parc',
                    STYLES: '',
                    format: 'image/png',
                    transparent: true
                }, 
                {
                    maxExtent: bounds,
                    isBaseLayer: false
                }
            );

            this.addLayers([untiled]);
        } else {
            //TODO
        }
    }
});

Answer 1

There are parameters, but there's an issue with XYZ layers. But there is a patch.

All the info is here: https://stackoverflow.com/a/4294980/229875

Answer 2

you create 2 styles, one standard, one temp , which is what you typically use when the feature is hovered, then you apply rules, that is the magic.

  var halte_temp_styled = new OpenLayers.Style({
      fillColor: "red",
      fontColor: "#000000",
      fontWeight: "normal",
      pointRadius: 8,
      fontSize: "11px",
      strokeColor: "#ff9933",
      strokeWidth: 2,
      pointerEvents: "all",
      fillOpacity: 0.3,
      label : "${name}",
      labelOutlineColor: "white",
      labelAlign: "rb",
      labelOutlineWidth: 8,
      cursor: "pointer",
      fontFamily: "sans-serif"
   });

  var halte_styled = new OpenLayers.Style({
      fillColor: "red",
      fillOpacity: 0.6,
      fontColor: "#000000",
      fontWeight: "light",
      pointRadius: 8,
      fontSize: "11px",
      strokeColor: "#ff9963",
      strokeWidth: 3,
      pointerEvents: "all",
      labelOutlineColor: "white",
      labelOutlineWidth: 8,
      labelAlign: "cm",
      cursor: "pointer",
      fontFamily: "sans-serif"
   });

   var halte_style = new OpenLayers.StyleMap({
      'default' : halte_styled,
      'temporary' : halte_temp_styled
   });

Then add the rules , who will influence the behavior of the (default) style, in the example below it will follow the scale of the layer and act accordingly. In this example, once you are zoomed at level 18, the labels of the feature will be displayed, else they will only be displayed when hovered over.

/* Style the halte layer acc to res */
   halte_style.styles['default'].addRules([
         new OpenLayers.Rule({
         maxScaleDenominator: 215000,
         minScaleDenominator: 27000,
         symbolizer: {
            fillColor: "red",
            fillOpacity: 0.6,
            fontColor: "#000000",
            fontWeight: "light",
            pointRadius: 4,
            fontSize: "11px",
            strokeColor: "#ff9963",
            strokeWidth: 2,
            pointerEvents: "all",
            labelOutlineColor: "white",
            labelOutlineWidth: 8,
            labelAlign: "cm",
            cursor: "pointer",
            fontFamily: "sans-serif"

            }
         }),

      new OpenLayers.Rule({
         maxScaleDenominator: 27000,
         minScaleDenominator: 3384,
         symbolizer: {
            fillColor: "red",
            fillOpacity: 0.6,
            fontColor: "#000000",
            fontWeight: "light",
            pointRadius: 10,
            fontSize: "11px",
            strokeColor: "#ff9963",
            strokeWidth: 3,
            pointerEvents: "all",
            labelOutlineColor: "white",
            labelOutlineWidth: 8,
            labelAlign: "cm",
            cursor: "pointer",
            fontFamily: "sans-serif"

            }
         }),
      new OpenLayers.Rule({
         maxScaleDenominator: 3384,
         minScaleDenominator: 1,
         symbolizer: {
            fillColor: "red",
            fillOpacity: 0.6,
            fontColor: "#000000",
            fontWeight: "light",
            pointRadius: 10,
            fontSize: "11px",
            strokeColor: "#ff9963",
            strokeWidth: 3,
            label : "${name}",
            labelAlign: "cm",
            //labelAlign: "cm",
            pointerEvents: "all",
            labelOutlineColor: "white",
            labelOutlineWidth: 8,
            cursor: "pointer",
            fontFamily: "sans-serif"
            }
         })
      ]);

In the vector layer in question you set this stylemap:

    styleMap: halte_style,

You probably could play as well with

minScale: 54168.1

On your vector layer. But that isn't as fine-grained as rules.