Hi Paul,
The main way it cuts down on repetitiveness is that it provides a way
to break out rules by class and specificity. Using xml entity
definitions, as I have, is frustrating because you have to work
backward from the Layer to the Style, coming up with an "unrolled"
representation of your rules and mapping that onto a set of
declarations. Emulating a class (e.g. "roads", "buildings") with
entities requires that you set up applicable styles in one spot, and
then maintain pointers to them in each Layer - the class is implicitly
defined by the styles it uses, though it may not be labeled as such
unless you're conscientious about commenting things. The process of
designing a Mapnik stylesheet effectively forces you to unroll classes
yourself.
I like the CSS way because it feels more DWIM ("Do What I Mean") -
setting up a class of things consists of adding class attributes to
layers, and decisions about how that class should be rendered are all
grouped together in a list of rules. It's a concrete representation of
what I'm trying to imitate with XML entities, yet still compatible
with Mapnik proper. There's a lot of process thinking that goes into
stylesheets which could definitely be replaced by code.
-mike.
On Aug 25, 2008, at 12:22 PM, Paul Smith wrote:
Hey Mike,
Looks really interesting. I took a glance at your code -- haven't
had a chance to play with it yet, but you've got a solid framework
here. I'm looking forward to testing it out.
I'm trying to wrap my head around it, and maybe I just need to spend
some more time with the docs and the code itself. Thinking about
cutting down on repetitiveness, how does mapnik-css improve over,
say, XML entity definitions?
Cheers,
-Paul
On Mon, Aug 25, 2008 at 11:44 AM, Michal Migurski <[EMAIL PROTECTED]>
wrote:
Hi,
Having worked on one Mapnik project that required big, almost-OSM-
scale stylesheets, I've been a bit frustrated with the state of the
art for defining map appearance. So, I've built a stylesheet
preprocessor that parses a format explicitly based on HTML + CSS and
outputs the usual XML styles.
There's a basic introduction here:
http://teczno.com/cascadenik/doc/
...and complete code here (note some of the reqs in the Makefile):
http://code.google.com/p/mapnik-utils/source/browse/trunk/serverside/styles/
I'm looking for comments / feedback.
It's a fairly complete thought, incorporating a lot of the things I
believe would make styling maps accessible to designers:
- It's possible to refer to external files in predictable locations
including images and linked stylesheets.
- Style definitions can work in a class-oriented fashion, allowing you
to express ideas such as "all roads are red, but primary roads have a
yellow edge and they're different widths at each zoom level" -
currently this is difficult or at least enormously repetitive with
existing Mapnik styles.
- Rules for how these definitions combine and cascade are also
explicit, copied directly from the CSS spec.
- I've also started to introduce useful shorthands, e.g. it's possible
to express scale denominator boundaries in a reduced "zoom" notation
specifically for maps in the Google / VEarth / OSM projection.
Most properties are done:
http://code.google.com/p/mapnik-utils/source/browse/trunk/serverside/styles/style.py#48
Outstanding items still on my list to do include the shield
symbolizer, dashed lines, and Filters.
Also a full set of edge & corner cases hasn't yet been dealt with, but
there are tests:
http://code.google.com/p/mapnik-utils/source/browse/trunk/serverside/styles/test.py
Anyway, thoughts welcome.
-mike.
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