[OSM-talk] Cross-renderer tag support, now with OSMdoc!

[Steve Bennett]

On Sun, Dec 20, 2009 at 4:41 AM, Dave F. <davefox at madasafish.com> wrote:

> This is looking useful.
>
> One thing it doesn't pick up on (& I'm not sure if it's possible) is to
> distinguish how a particular renderer deals with rendering areas.
>
> For instance pubs in Mapnik are rendered as POI's even if is mapped as an
> area:
>
> http://osm.org/go/eukOiNU7b--
>
>
I may be able to do something with this for some renderers...it depends.


>
> To check I understand:
>
> barrier=* means that any barrier tag should be rendered, yes?
>

No. You can't perform trivial analysis of this kind and expect to reach
conclusions about what will and won't be rendered. All it can really do is
make guesses based on what tests the renderer is performing.

If "barrier=*" appears in the table for a renderer, all this means in
practice is that the renderer performs a test as to whether the key is
barrier, without immediately qualifying it with a value test in the same
expression.

In this instance, Mapnik has the following style:
    <Rule>
      &maxscale_zoom16;
      <Filter>[barrier] <> '' and not [barrier] = 'hedge'</Filter>
      <LineSymbolizer>
        <CssParameter name="stroke">black</CssParameter>
        <CssParameter name="stroke-width">0.4</CssParameter>
      </LineSymbolizer>
    </Rule>

As I read that, Mapnik will draw any barrier that is not a hedge as a black
line. But as pointed out, this presumably only applies to ways because it's
a LineSymbolizer rather than a PointSymbolizer.

It looks possible to use the node/way/area distinction, but it will be
difficult to avoid overloading the table with information.

How often does your list refresh?
>

At my whim, atm. I don't have any infrastructure for doing it automatically,
but I intend to publish the source in a way that someone else could easily
re-run it, and then maybe it could be done on a regular basis.


>
> Is it worth adding Cycle Map?
>

Probably - I'll have a look. It's just a different stylesheet for Mapnik
afaik, but that doesn't make it less useful.

Steve
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