[OSM-talk] simplifying mapnik layout definition

[Dave Stubbs]

On Tue, May 27, 2008 at 3:40 PM, Andreas Barth <aba at not.so.argh.org> wrote:
> Hi,
>
> currently the mapnik layout definition is a bit complex. Please consider
> this example:
> <Style name="tunnels-casing">
>    <Rule>
>      <Filter>([highway] = 'motorway' or [highway]='motorway_link') and ([tunnel] = 'yes' or [tunnel] ='true')</Filter>
>      <MaxScaleDenominator>200000</MaxScaleDenominator>
>      <MinScaleDenominator>100000</MinScaleDenominator>
>      <LineSymbolizer>
>        <CssParameter name="stroke">#506077</CssParameter>
>        <CssParameter name="stroke-width">3</CssParameter>
>        <CssParameter name="stroke-dasharray">4,2</CssParameter>
>      </LineSymbolizer>
>    </Rule>
>    <Rule>
>      <Filter>([highway] = 'motorway' or [highway]='motorway_link') and ([tunnel] = 'yes' or [tunnel] ='true')</Filter>
>      <MaxScaleDenominator>100000</MaxScaleDenominator>
>      <MinScaleDenominator>20000</MinScaleDenominator>
>      <LineSymbolizer>
>        <CssParameter name="stroke">#506077</CssParameter>
>        <CssParameter name="stroke-width">5.5</CssParameter>
>        <CssParameter name="stroke-dasharray">4,2</CssParameter>
>      </LineSymbolizer>
>    </Rule>
> [ 2 more cases ]
>
>
> The differences are only within the scales. So it would make sense to
> split the scales off - and make them as small as possible. The smaller
> it is, the easier one can make changes. So this could be written as:
>
> <Style name="tunnels-casing">
>      <Rules filter="([highway] = 'motorway' or [highway]='motorway_link') and ([tunnel] = 'yes' or [tunnel] ='true')"/>
>      <CssParameter name="stroke">#506077</CssParameter>
>      <CssParameter name="stroke-dasharray">4,2</CssParameter>
>      <ScaleDenominator max="200000" min="100000">
>        <CssParameter name="stroke-width">3</CssParameter>
>      </ScaleDenominator>
>      <ScaleDenominator max="100000" min="20000">
>        <CssParameter name="stroke-width">5.5</CssParameter>
>      </ScaleDenominator>
>    </Rules>
>
>
> This drops the (IMHO unnecessary) LineSymbolizer (one can make it up
> from the stuff around it) and emphasizes the differences. If this looks
> ok-ish, I could write an converter from the new to the old format as an
> starter.


I don't think inferring the LineSymbolizer is a good idea. But if you
want to write a preprocessor to do the scale extraction I think that
might help a lot.
Personally I'd like to see an end to the XML syntax as it's hard to
read, but that's more work than it's worth right now (to me at least).

Dave