Re: [Geoserver-users] Labeling Polygons

[Andrea A. <aa...@op...>]

David Winslow ha scritto:
> GeoServer only takes into account the current viewing area when 
> rendering.  OpenLayers, by default, loads up a map by fetching lots of 
> 256x256 pixel tiles, rather than asking geoserver to render a lot of 
> area you've already fetched when you pan just a little bit.  If you set 
> your OpenLayers or other map client to "untiled" mode, then you will 
> never see repeated labels.  This will keep your browser from being able 
> to cache tiles and such, though, so expect a higher load on GeoServer as 
> a result.

Err... I would disagree about the load. We had to make countless 
adjustements to GeoServer and the OL used in the preview to avoid
tiled OL to kill GeoServer with an enormous load, and from a single
client. This includes setting the buffer to 0 and using the control-flow
to disallow the client to make 20-50 request in parallel (the browser
will actually do "only" 6, but if you start zooming using the scroller
they will pile up).

Long story short, the client will seem less responsive when panning,
but the load on the server will be a lot smaller afaik.

Tiling has been created by Google with the usage of heavy tile caching,
and in a way that precomputes statically all label positions taking
into account that the requests that the client will ever made are
just the predetermined tiles.
Pretending to use tile caching against a dynamic WMS is, in my opinion,
just plain wrong.

As for labelling, unfortunately atm we don't have a function to 
precompute in a global way all the labels for a certain zoom level
as a single enormous request. Imho Google does this with a massive
map/reduce using a ton of resources, so if we'd like to replicate it
we'd have to do the same.

Cheers
Andrea



-- 
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.