Re: [Geoserver-users] polygon label repeated for each tile

[Andrea A. <and...@ge...>]

On Wed, Aug 15, 2012 at 4:40 PM, Rahkonen Jukka
<Juk...@mm...>wrote:

> I made a quick test with 22339 rather complicated polygons and
> PointOnSurface function in Spatialite.  Result looks pretty good with all
> the points well inside their polygons which was a nice surprise. I was
> remembering from the past that point on surface is not usable for labeling
> because when I last tried the same function with Oracle it simply placed
> the points on surface into the first outer ring vertices. Perhaps Oracle
> does it in a more clever way nowadays.  Somehow I feel that PostGIS behaves
> a lot like Spatialite.
>
> I feel that point on surface could be a reasonable candidate for label
> anchor point. Problem with Geoserver is that all backends would not behave
> in a similar way. It could perhaps be possible to a sort of a simulation by
> creating a point layer with PointOnSurface and  use that for labeling.
> Perhaps it does not tell anything about how well partial labels from
> adjacent tiles match.
>

If the spatialite algorithm works fine it's worth checking out how that is
done. Is it using OGR maybe?
There is a similar function in JTS, but now sure how well that matches a
good label point:
http://tsusiatsoftware.net/jts/javadoc/com/vividsolutions/jts/geom/Geometry.html#getInteriorPoint()

We could roll a WPS process to do that, in case people want to use it as a
starting point and then
eventually manually edit the data.
However the WPS process (chained with gs:Import to feed the data back in
the db) would create
a whole new layer, the user would have to drop the original one by hand.


>
> Those who use tiles can motivate themselves to coding by thinking that if
> the system is able to match partial labels there would be no need for
> creating oversized metatiles. This could mean less pixels to create when
> seeding the cache and thus more speed.
>

Hmm... the metatatiles are actually not oversized afaik, the previous mail
stated "oversized tiles" which I believe means metatiles.


>
> By the way, can Geoserver utilize several geometry columns in one table in
> Oracle, PostGIS and Spatialite? If yes, users could pre-process the data
> and create label points into their own geometry fields, as well as
> simplified geometries to be used at small scales.  It would not make
> database much bigger because there would be no need to copy the attributes.
>

Yes, it can

Cheers
Andrea


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