[Talk-us] Fwd: Re: [OSM-talk] Mapquest launches site based on OSM!

[Phil! Gold]

* Toby Murray <toby.murray at gmail.com> [2010-07-19 13:54 -0500]:
> I see shields being rendered for ways that have multiple ref values:
> http://open.mapquest.co.uk/mq/7-_nm8O2RaRCO5sLEy

Huh.  I don't see anything in the stylesheet to do that.  Perhaps they're
splitting the ref during the database import.

> Has there ever been any consideration for using the symbol= tag in the
> route relationships to dynamically pull in shields from the listed
> source?

I don't know whether it's been considered for the main slippy map.  I had
the thought to use it when I started looking at shield rendering, but it's
kind of difficult to do with Mapnik.  Mapnik needs the image names to be
specified explicitly in the stylesheet, so you'd have to add a
preprocessing step that downloaded the images and wrote part of the
stylesheet with a separate rule for each different shield.  In contrast,
using the ref tags (either on the ways or the relations) lets you use just
one relation for each type of shield, not each individual route.  That
cuts down on the size of the stylesheet, and speeds up Mapnik, since there
are fewer rules to test against.

Mapnik 2 (still in development) supports choosing images dynamically, but
I don't think it can download SVGs (or PNGs, for that matter) from the
Internet, so you'd still need a little more preprocessing to do those
downloads before you render.

-- 
...computer contrarian of the first order... / http://aperiodic.net/phil/
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