[OpenLayers-Users] Display a layer at the specified zoom

[Mario Danelli]

adidas <xkadidas at ...> writes:

> 
> Hello! How to display a layer at the specified zoom? For example, the 
> layer is displayed at a zoom more than 14 and etc.
> Thanks for answer.
> 

If the layer is a tile layer a solution, probably not the best, could be this:

- Create a new layer called "special layer"

var layer = new OpenLayers.Layer.OSM( "special_layer", "./tiles/special_layer/", 
{                               type: 'png', 
				getURL: get_my_url_special_layer, 
				isBaseLayer: false 
			});
			

- Specify "special layer" as additional layer over the base layer

map.addLayers([mapnik, special_layer]);
	

- Implement a "get_my_url_special_layer" function that return null if the level 
is less the one specified with "your_layer" and the tile png in other cases.


function get_my_url_special_layer(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();
	

	if (y < your_limit) {
		return null;
	} else {
	        url = this.url;
		path= "speciallayer/" + z + "/" + x + "/" + y + "." + this.type;
		if (url instanceof Array) {
			url = this.selectUrl(path, url);
		}
		return url+path;
	}
}

If instead, the layer is simply a marker layer you can implement a function that 
handle the zoomend event:

	map.events.register('zoomend', this, function(e) {
			var x = map.getZoom();
			
			if (x < your_layer){
				special_layer.setVisibility(false);
			} else {
				special_layer.setVisibility(true);
                        }
			
	});