Osmarender/svg open09

Notes for presentation at SVG Open 2009

30,000ft Overview

osmarender takes stylesheet, filters data through rules and outputs SVG. close-areas.pl, lines2curves for pre/post-processing.

Then Tiles@Home, distributed rendering platform, clients run the transformation and rasterizes to PNG tiles.

Bugs and issues

• Too hard to do changes across zoom levels, we probably need a meta-stylesheet.

Challenges

• find midpoint of a polygon
• Square line caps
• Core/casing
• Seams
• Fonts
  • We should look at SVG fonts, http://trac.openstreetmap.org/ticket/1228
• Duplicate labels / proper label placement algorithm

Architecture

• XSL implementation compared to perl version

Rendering

Both use incredible amounts of memory/other resources, 4GB T@H client dies every now and then due to OOM. Note that this is why we need a whole distributed architecture with several hundred clients to do rendering.

T@H, and especially the SVG::Rasterize module, is a study in Batik and Inkscape bugs.

• Inkscape
  • Brittle, handles failures badly
    • Corrupting preferences bug
    • Windows version pops modal dialogue
  • Doesn't seem to return the same return codes for various failures across versions or platforms
• Batik