FW: FW: [Openstreetmap] Recent improvements to the editing applet

Tom Carden tom at tom-carden.co.uk
Wed Jan 4 23:19:20 GMT 2006

On 1/4/06, Matt Amos <matt at matt-amos.uklinux.net> wrote:
> would it be better to request three tiles, e.g:
> 1) the opaque "background" tile from landsat
> 2) the breadcrumbs on a transparent PNG
> 3) the roads on a transparent PNG

I suggested a move back to this method for the viewer a while ago (I
think there's a ticket for it too!
http://www.openstreetmap.org/trac/ticket/42).  So then the viewer and
the applet can share a cache - the viewer drawing its own editable

It would be a really nice thing to be able to cache landsat
indefinitely - sometimes the NASA server is really slow.

Also - as others have mentioned - this frees up the possibility of
distributing the load, and of compressing each layer more efficiently
(it certainly wouldn't be double the bandwidth).  What hasn't been
mentioned is that it also gives the client the ability to choose which
things are shown - a generalised layering interface would be a really
useful thing.  I for one would like to show the GPS tracks in the
viewer (so I know where needs editing), and I know others would like
to display things from external WMS servers.

Steve - what were the disadvantages of client-side compositing?  Did
it just get dropped because of the move to the (originally civicmaps)
tile script?

> that way the client could deliberately request (2) and (3) with a
> special form of URL (maybe appending ?cache=no or something) which
> would have the side effect of invalidating the server cache for just
> those tiles?
> an alternative idea is that the client could re-render the tiles
> itself (and possibly upload them) so you'd always have the latest
> information on your screen.

You can force refresh with your browser (ctrl-refresh or alt-refresh I
think, in Firefox at least) - I assume that's an HTTP header for a GET
request... the applet could issue those in the background for any
tiles where vectors have been edited, and (perhaps only for logged in
users) I'm pretty sure we could offer a 'refresh visible tiles' button
on the viewer.  (Thought - can an HTTP HEAD request refresh a cached
image without downloading it?)

> anybody fancy implementing a REST-ful API for the tiles? something
> like http://www.openstreetmap.org/api/0.2/tile/4/2,3 gives the tile
> x=2, y=3 for zoom level 4. then you could PUT the rendered tiles
> there and have the server backend figure out how to invalidate the
> cache...

That would be neat, but do we really want clients in charge of rendering?


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