Jeffrey Warren wrote:
Collaborating on a spec would be great. Cascadenik is so much more
legible than SLD, but you're right, that's probably because I'm so
comfortable with CSS. One advantage to using JSON-compliant markup is
that styles don't have to be static. This works well for pure
JavaScript/HTML renderers like Cartagen and OpenLayers, but not as well
for Mapnik... maybe there's a way to gracefully degrade.
Example:
way: {
strokeStyle: function() {
return "#"+(parseInt((this.user),36).toString(16)+"000000").truncate(6,"")
},
lineWidth: 2,
fillStyle: "white"
}
Kind of hacky, but it yields:
http://map.cartagen.org/?gss=http://unterbahn.com/cartagen/style.gss
...that is, it colors ways by author name - i see a lot of "crschmidt"
in there :-)
I'm looking through the SLD spec and it looks like it does not specify
event handlers, though of course OpenLayers has the Control class. It'd
be great to preserve that kind of scripting power in a style standard.
It's not explicitly in the SLD specification, but rather in the Filter
specification that SLD builds upon. There are 'expressions' in Filters
that can take 'functions'.
I'm not sure how much a standard should really have specific scripting
stuff in it, as you pretty much have to commit to a particular scripting
language. But you should be able to extend the standard to get at that,
in functions we do things like evaluate freemarker templates. We've
been doing dynamic symbolizers based on values of the data, see
http://blog.geoserver.org/2008/12/08/dynamic-symbolizers-part-1/ But
it's a bit of a hack on the spec.
So you don't need JSON to do dynamic styles, and if we want to make a
styling language that is used by more than javascript clients we
probably shouldn't try to stick to JSON.
Another thing I was wondering about is whether there's a source for OSM
data in GeoJSON? It would be great not to have to parse OSM xml into
json for every request, so I'm considering running a weekly planet.osm
source to serve GeoJSON... is that available already?
You can use GeoServer to generate GeoJSON through WFS from OSM data, see
http://blog.geoserver.org/2009/01/30/geoserver-and-openstreetmap/
We have some servers set up with OSM data, but I don't think we're
regularly updating them.
best regards,
Chris
Best,
Jeff
On Mon, Apr 27, 2009 at 11:11 AM, Chris Holmes <[email protected]
<mailto:[email protected]>> wrote:
Christopher Schmidt wrote:
On Sun, Apr 26, 2009 at 02:41:36PM -0400, Jeffrey Warren wrote:
Absolutely, Christopher - I'm a big admirer of the
OpenLayers community, and
the things you can do with it are impressive. Still, I
haven't seen an
implementation of an entire map in vector on the client side
- examples such
as this:
http://openlayers.org/dev/examples/wfs-reprojection.html
...which are great, still use a pre-rendered tile base
layer. What I'm
hoping is that by sending *only* vector data, mappers can
completely design
maps from the ground up with their own GSS stylesheets.
Like http://crschmidt.net/mapping/choropleth.html ? (Note that the
styling suppot here was written before SLD support was
implemented, and
could now be done entirely using SLD instead of custom OpenLayers
rules.)
Contributing to OpenLayers++
Cartagen looks to have some cool ideas, but it'd be really awesome
if it was done by improving OpenLayers core and being a thin layer
on top that's optimized for Android and iPhone.
We've been thinking about GSS/Cascadenik type ideas, but having it
go to and from OpenLayers Style objects, as an alternative to SLD.
See http://opengeo.org/services/coredevelopment/openlayers/css_styling/
It'd be really great to have a web designer friendly alternative to
SLD. It may be a bit too early right now, but at some point we
should start an adhoc spec group, following on the successes of
GeoRSS, GeoJSON, and WMS-C, to make a standard for CSS for Map
Styling. It'd be great to be able to share styles between
GeoServer, Mapnik and MapServer, and to use Openlayers as a cross
platform style editor (or the common basis for different approaches
to map styling). We'd be interested in collaborating on a spec, and
on implementations for OpenLayers and GeoServer.
Chris.
Regards,
--
Chris Holmes
OpenGeo - http://opengeo.org
Expert service straight from the developers.
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