function customLayer(layerParameters) {
	
	_layer.apply(this,[layerParameters]);
	
	for (var p in _layer.prototype) {
		if (!customLayer.prototype[p])
			customLayer.prototype[p]= _layer.prototype[p];
	}
 };

// redefine setTile
customLayer.prototype.setTile = function(img) {
    var l = safeParseInt(img.style.left) + this._map.kaMap.xOrigin;
    var t = safeParseInt(img.style.top) + this._map.kaMap.yOrigin;
    
    // dynamic imageformat
    var szImageformat = '';
    if (this.imageformat && this.imageformat != '') {
        szImageformat = '&i='+this.imageformat;
    }
	        
	var szScale = "&s=" + this._map.aScales[this._map.currentScale];
	var groupName = "&g=" + this.name;

	var src = "http://"+subDomain+".kamap.swissgeo.ch/OPO/tile_customLayer.php" +
				't=' + t + '&l=' + l + groupName + szScale + szImageformat;
	
	if (arguments[1]) {
		src += '&force=true';
	}
	
	if (img.src != src) {
		img.style.visibility = 'hidden';
		img.src = src;
	}
};