Hi, 80n wrote: > Can someone remind me again please. What's the purpose of calculating and > storing the bbox for each changeset?
So that it is possible to query the database effectively for something like "all changesets possibly affecting London". Without changeset bboxes this would mean retrieving all nodes in the London bbox, then retrieving all ways that use these nodes, then retrieving all relations that use these nodes or ways, then retrieve all changesets that affect any of these ways, nodes, or relations, and then return them. This would be a very expensive operation - and we expect *many* people to make these queries in regular intervals as they're keeping a "watch" on their area! Of course the expensive method sketched above has the advantage of only returning changesets that really affect the area in question, whereas the bbox method we're using might also return a changeset that has one edit in Southampton and one in Cambridge... but even if we want the precision of the expensive method, the bbox method can be used as a kind of index. Bye Frederik _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
