public static Viewport intersect(final Viewport vp1, final Viewport vp2) {
        return intersect(Arrays.asList(vp1, vp2));
    }
internal worker function for
- containing(Points)
- containingGCLiveCaches(Geocaches)
- containingCachesAndWaypoints(Geocaches)
main/src/main/java/cgeo/geocaching/location/Viewport.java