[Tilesathome] RFC: Symbols rendering

[Knut Arne Bjørndal]

On Sat, Sep 13, 2008 at 09:27:22AM +0200, Jiri Klement wrote:
> >> 2) Draw icon in area center only when there is no node inside of area
> >> with the same tags.
> >
> > I wouldn't bother about this, I've mostly seen this where you have a
> > parking space that's input twice, as both area and node. That was
> > basically a renderer workaround for before the renderers did symbols
> > for areas.
> 
> Yes, it's workaround and if rendering rules stayed the same as now, it
> will be unnecessary. But I was thinking I will add support for more
> features applicable to both nodes and areas. For example big
> place_of_worship is usually tagged as both node and area. If I change
> rendering rules to add area symbol, I'll get thousands of churches
> with two icons.

Then the solution is again to fix the data, imho.

> > If we want to do anything about these nodes at all I'd rather convert
> > them into labels using the relation, thus actually fixing the data
> > instead of adding a workaround to handle an old workaround.
> 
> This will be cleaner solution, but I'm afraid there is already too much data.

I wasn't thinking about doing this manually, but with a script that
goes over the planet and changes everything. I think scripts to do
that kind of fixing exist somewhere.

> >> Checking whether point is inside of polygon is quite simple, it should
> >> be possible to do in xslt in reasonable time. Anyway I'm planing to
> >> extend area-center preprocessor help osmarender with it.
> >
> > Point-in-polygon is not all that simple, it's definitely not cheap
> > (pretty much no matter how you implement it).
> 
> I think it's quite cheap. You get points in boundbox, it should be
> just one XPath query. Then you make horizontal line going through
> every point and count number of intersections with area edges. If the
> number is odd, then point is inside of polygon.

I think it's something like O(n^2) plus a bit with n being the number
of nodes in the polygon. That's not my idea of cheapness.

Just so you know there is a reason why I made the areacenter wrapper
not try running the fancy areacenter on anything with more than X
nodes, and it's precisely these kinds of calculations.

-- 
Knut Arne Bjørndal
aka Bob Kåre
bob+osm at cakebox.net
bobkare at irc
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