Get the distance to the weatherstation from wstation section of xml.

    wstation: weerstation section of buienradar xml (dict)
    latitude: our latitude
    longitude: our longitude

def __get_ws_distance(wstation, latitude, longitude):
    """Get the distance to the weatherstation from wstation section of xml.

    wstation: weerstation section of buienradar xml (dict)
    latitude: our latitude
    longitude: our longitude
    """
    if wstation:
        try:
            wslat = float(wstation[__BRLAT])
            wslon = float(wstation[__BRLON])

            dist = vincenty((latitude, longitude), (wslat, wslon))
            log.debug("calc distance: %s (latitude: %s, longitude: "
                      "%s, wslat: %s, wslon: %s)", dist, latitude,
                      longitude, wslat, wslon)
            return dist
        except (ValueError, TypeError, KeyError):
            # value does not exist, or is not a float
            return None
    else:
        return None