[OSM-dev] Slippy map way forward -- OpenLayers and/or Mapstraction?

Erik Johansson erjohan at gmail.com
Sat Jul 1 14:41:10 BST 2006

On 7/1/06, Christopher Schmidt <crschmidt at crschmidt.net> wrote:
> On Sat, Jul 01, 2006 at 02:54:25PM +0200, Erik Johansson wrote:
> > On 7/1/06, Christopher Schmidt <crschmidt at crschmidt.net> wrote:
> > >On Sat, Jul 01, 2006 at 02:38:49PM +0200, Erik Johansson wrote:
> > >> On 6/30/06, Anselm Hook <anselm at hook.org> wrote:
> > >> >
> > >> >Much as I am endeared to tile.js I'd personally just suggest making sure
> > >> >the backend can act as a WMS.  This would open the door to a variety of
> > >> >possibilities including OL.
> > >> >
> > >> >OL avoids speaking as to how the back end is supposed to keep up with
> > >all
> > >> >the queries but probably squid can address that?
> > >>
> > >> Have anyone made a Squid backed WMS server? As far as I know Mapserver
> > >> has no support for Cache control.
> > >
> > >There is no reason that you can't set cache timeouts using mod_cache --
> > >I do this on most of my WMS services. This makes them cachable by
> > >browsers and squid.
> >
> > You mean as in setting a 48h timeout, that's easy to do in Squid. But
> > can you check if a BBOX has been updated?
> No. This is one of the long-term existing problems with OSM tiles

Ok, it should be very fast to see if something has changed on a OSM
tile, this should do it. (though you need to move a node to get an

select max(timestamp) from nodes where latitude > #{lat2}  and
latitude < #{lat1} and longitude > #{lon1} and longitude < #{lon2}

Though how do you convey that information though Mapserver? It's
completely useless otherwise, and the only way to solve the cache is
by doing ugly hacks  such as file cache and squid purge.

These are ugly hacks because there are so many tiling schemes around
that there is no feasable way to understand each of them when writing
the script that purges from the cache.

>   http://trac.openstreetmap.org/ticket/121
> This is part of the reason why I mentioned that heading towards a
> file-cache, where the location of tiles is on disk and therefore easily
> under control

So does open layers have support for file cache? I know Kamaps allow
you do precache tiles from the WMS server down to a file cache, but
that means you have the same problem..



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