OpenStreetMap

migurski has commented on the following diary entries

Post When Comment
Is the OpenStreetMap Rails App Appropriate for Other Data Sets? over 1 year ago

It’s a less important point, but the XML output uses seven digits of precision after the decimal point, and for data sets like land use it might be more appropriate to use 3-4. Less important, though.

Is the OpenStreetMap Rails App Appropriate for Other Data Sets? over 1 year ago

One interesting outcome will be to gauge the suitability of the OSM tool chain for data at a different scale, like forest outlines vs. roads. How many of the tools assume street-scale in all things, and enforce that in minimum zoom levels for editing (iD) or high-precision data output (planet XML)?

Rendering is a Pain over 4 years ago

On further thought, it's probably worth noting that Mapnik's processing pipeline, the way that styles must be specified before geometry is passed through, is a major constraint here. I could imagine a future modification to Mapnik where it behaves more like HTML + CSS and applies the rules in-flight as they are needed, and removes the need to prepare all possible combinations. I expect this is many versions off, though.

Rendering is a Pain over 4 years ago

Hi asciiphil,

Cascadenik is my project, thanks for your comments. The combinatorial explosion issue is very much something I've run into when developing stylesheets, and like you I've found myself pushing a lot of logic in SQL to fix the problem. Here, for example, is a SELECT statement from one recent project: http://dpaste.com/hold/190143/

The "is_tunnel" and "is_bridge" parts help handle the various different ways of saying "yes", and the "kind" result column groups together many different types of roads. There's also a subselect in there you might have noticed: it groups the lines from each layer into single MULTILINE geometries, which helps deal with certain casing issues. Ultimately this is the way I've made stylesheets workable for myself - keep the ability to separate line casings and widths and colors and zoom levels, and use the expressiveness of SQL to munge the planet database into something more directly applicable to rendering. I know that Cloudmade have done similar things, including I believe downsampling the detail level of the road vectors for certain rendered zoom levels.