+ ##
+ # 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 ||= [ min_lon, min_lat, max_lon, max_lat ]
+ 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!(array)
+ # ensure that bbox is cached and has no nils in it. if there are any
+ # nils, just use the bounding box update to write over them.
+ @bbox = bbox.zip(array).collect { |a, b| a.nil? ? b : a }
+
+ # FIXME - this looks nasty and violates DRY... is there any prettier
+ # way to do this?
+ @bbox[0] = array[0] + EXPAND * (@bbox[0] - @bbox[2]) if array[0] < @bbox[0]
+ @bbox[1] = array[1] + EXPAND * (@bbox[1] - @bbox[3]) if array[1] < @bbox[1]
+ @bbox[2] = array[2] + EXPAND * (@bbox[2] - @bbox[0]) if array[2] > @bbox[2]
+ @bbox[3] = array[3] + EXPAND * (@bbox[3] - @bbox[1]) if array[3] > @bbox[3]
+
+ # 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
+ 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
+
+ def tags_as_hash
+ return tags
+ end
+