+ ##
+ # returns the bounding box of the changeset. it is possible that some
+ # or all of the values will be nil, indicating that they are undefined.
+ def bbox
+ @bbox ||= BoundingBox.new(min_lon, min_lat, max_lon, max_lat)
+ end
+
+ def has_valid_bbox?
+ bbox.complete?
+ end
+
+ ##
+ # expand the bounding box to include the given bounding box. also,
+ # expand a little bit more in the direction of the expansion, so that
+ # further expansions may be unnecessary. this is an optimisation
+ # suggested on the wiki page by kleptog.
+ def update_bbox!(bbox_update)
+ bbox.expand!(bbox_update, EXPAND)
+
+ # update active record. rails 2.1's dirty handling should take care of
+ # whether this object needs saving or not.
+ self.min_lon, self.min_lat, self.max_lon, self.max_lat = @bbox.to_a if bbox.complete?
+ end
+
+ ##
+ # the number of elements is also passed in so that we can ensure that
+ # a single changeset doesn't contain too many elements. this, of course,
+ # destroys the optimisation described in the bbox method above.
+ def add_changes!(elements)
+ self.num_changes += elements
+ end
+