public <T extends ICoordinate> Collection<T> filter(@NonNull final Collection<T> points) {
        final Collection<T> result = new ArrayList<>();
        for (final T point : points) {
            if (point != null && contains(point)) {
                result.add(point);
            }
        }
        return result;
    }
Filter return the points present in the viewport.

@param points a collection of (possibly null) points
@return a new collection containing the points in the viewport
main/src/main/java/cgeo/geocaching/location/Viewport.java