function addPolylineElevation($polyline_id, $elevation_dom_id, $samples=256, $width="", $height="", $focus_color="#00ff00"){
		if(isset($this->_polylines[$polyline_id])){
			$this->_elevation_polylines[$polyline_id] = array(
				"dom_id"=>$elevation_dom_id,
				"samples"=>$samples,
				"width"=>($width!=""?$width:str_replace("px","",$this->width)),
				"height"=>($height!=""?$height:str_replace("px","",$this->height)/2),
				"focus_color"=>$focus_color
			);
		}
	 }