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GPU-accelerated rendering PBF files onto an interactive canvas.

Rendering of Melbourne CBD

Melbourne's CBD, minus the Yarra river which is now a void.

Legend:

  • Yellow: Road
  • Blue: Rail (tram and train) line
  • Green: Park land
  • Grey: Building footprint
  • Orange dots: Footpath

Overview

OpenGL 4.10 (thanks Apple) is used as the graphics API for rendering these files. To achieve this, I created a relatively light-weight wrapper over the raw OpenGL calls (provided by the gl crate) to assist with the creation of the shader programs and associated buffers, uniforms, etc. OpenGL was originally chosen due to my familiarity with it, however I'm interested in porting this to WGPU at some point for better compatibility.

The PBF files are loaded and processed on the CPU, with the ways (OpenStreetMap terminology for what's effectively a collection of nodes representing something, such as a building or a road) filtered out to only include objects of interest (namely roads, parks, buildings, and railways, which occurs in /src/osm/way.rs). These objects of interest then have bespoke rendering rules (defined per object in /src/objects/*.rs) which effectively boil down to drawing either a line and/or some fill. These rendering instructions and node data is all packaged up and sent over to the GPU which will generate any required geometry (such as each of the rectangles for a dashed line or rounded vorners). This technique offers a number of benefits, including minimising the amount of data that needs to be sent to the GPU and the time that the CPU spends processing the data. It also decouples the interpretation and style of the map objects from the underlying graphics API, (theoretically) making it simpler to migrate at some point.

The renderer has a perspective camera, and is looking down at a 2D plane in a 3D environment. This allows (fairly trivially) for extrusions and models to be included on the map, such as extruding the building footprints, or including models for traffic and other dynamic elements. This could even extend to plugging 'real world' data sources in (such as traffic or public transport timetables) to view them in real time on the map. In order to handle mouse interactions with the map (such as clicking and panning), some slightly curly maths was required to project the mouse from camera space into world space, but the resulting effect is very plesant to use!

Resources

  • Overpass - Query and select data, and export it to a number of different files
  • OSM Export - Easily grab and export a bounding box on a map

OSM Queries

Get residential roads within the bounding box

[timeout:25][bbox:-37.796223, 144.928243, -37.796100, 144.928732];

(
  way["highway"="residential"];
);

out body;
>;
out skel qt;

Other Notes

Getting data into PBF format

  1. Download desired data from one of the links above (export raw data from Overpass API)
  2. Download and compile osmconvert: http get http://m.m.i24.cc/osmconvert.c | cc -x c - -lz -O3 -o osmconvert
  3. Run the following command to perform the conversion: cat [downloaded file] | ./osmconvert - --out-pbf -o=[PBF output file]