On 21 Apr 2008, at 18:00, [EMAIL PROTECTED] wrote:
From: Tom Hughes <[EMAIL PROTECTED]>
Date: 21 April 2008 14:48:56 BDT
To: talk@openstreetmap.org
Subject: Re: [OSM-talk] SVG tiles
In message <[EMAIL PROTECTED]>
elvin ibbotson <[EMAIL PROTECTED]> wrote:
I had been intending to get round to mailing this list enquiring if
SVG downloads were possible/available when the Export tab appeared.
My initial delight** was slightly diminished when I exported a map in
two formats - SVG and PNG - and found the SVG version was 340kB while
the PNG file was 132kB. A glance at the SVG data suggests that text
is actually drawn (sometimes more than once (for background then
again for the text itself) using long, elaborate paths and shape
definitions of every character at every orientation and size, rather
than just using the SVG text element!!! I suspect it also
incorporates bitmap images as icons rather than using SVG
definitions. I think SVG is the way forward, but not if the file
sizes end up almost three times bigger than bitmaps!
Some of the text is drawn twice in order to get the halo effect
that our mapnik stylesheet uses. The icons are bitmaps because, as
I believe I explained yesterday, mapnik does not (currently) support
vector symbols. If you want to help with that I'm sure Artem will be
pleased to here from you.
Everything else is essentially down to cairo, which is the rendering
library that mapnik uses to render vector maps. I ask it to render
text using a given font and if it chooses to convert that to a path
then that is because it thinks it isn't possible to do it as a text
render for some reason.
In general terms SVG is pretty verbose anyway, so it's not at all
clear to be that it's ideal for what you are doing.
I would also point out that the export service was really designed
for people doing one of exports and not to act as a back end for the
sort of thing you're doing and it is unlikely to scale well to
supporting large scale use of that sort.
Fair enough! It sounds like SVG export from Mapnik/Cairo is a little
sub-optimal :-) I wasn't suggesting applications somehow used the
export service but that SVG tiles should be available alongside (and
ultimately instead of?) bitmap tiles
I suggest that, if has not already been done and is hidden somewhere
I haven't looked, that a server should be dedicated to scalable map
tiles using a compact and efficient implementation of SVG coding.
Sure. I'll just look in the cupboard marked "spare servers" and pull
out a server for you. Then I'll go write stack of code and deploy and
manage it for you.
Great, thanks.
Seriously. You want it, you write it.
Aw shucks. You guys are so much better at it than me.
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