public void startElement(String uri, String localName, String elementName, Attributes attributes) {
		
		if (TAG_TRACK_POINT.equals(elementName)) {
			foundTrackPoint = true;
			
			if(attributes.getLength() == 2) {
				for(int i=0; i<attributes.getLength(); i++) {
					if(attributes.getQName(i).compareTo("lat") == 0) {
						latitude = attributes.getValue(i);
					} else if(attributes.getQName(i).compareTo("lon") == 0) {
						longitude = attributes.getValue(i);
					} else {
						System.out.println(LABEL + "invalid attribute in trkpt element: " + attributes.getQName(i));
					}
				}
			} else {
				System.out.println(LABEL + "there must be two attributes (lat and lon) in the trkpt element");
			}
			
			elevation = null;
			time = null;
		} else if(TAG_ELEVATION.equals(elementName)) {
			foundElevation = true;
		} else if(TAG_TIME.equals(elementName)) {
			foundTime = true;
		}
	}