[OSM-dev] API 0.6: Changeset Access

[80n]

On Thu, Jan 29, 2009 at 10:08 AM, Frederik Ramm <frederik at remote.org> wrote:

> 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.
>

Thanks, Frederik, that makes sense.  I don't think I'd seen that use
expressed anywhere up to now, but then I haven't really been paying that
much attention to the 0.6 story.

80n



>
> Bye
> Frederik
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/dev/attachments/20090129/a85a29c6/attachment.html>