README.md

npm install glob canvas leftpad rainbow-dash moment

preprocess_race.js

var glob = require('glob'),
    fs = require('fs'),
    dsv = require('dsv'),
    moment = require('moment');

var paths = [];

var stops = dsv(',').parse(fs.readFileSync('../data/stop_times.txt', 'utf8'));

var stopid = null, points = [];

function timeSeconds(s) {
    var pts = s.split(':');
    return (parseInt(pts[0], 10) * 60 * 60) +
        (parseInt(pts[1], 10) * 60) +
        (parseInt(pts[2], 10));
}

for (var i = 0; i < stops.length; i++) {
    if (stopid !== stops[i].trip_id && points.length) {
        paths.push(points);
        points = [];
        stopid = stops[i].trip_id;
    }
    points.push({
        dist: parseFloat(stops[i].shape_dist_traveled),
        time: timeSeconds(stops[i].arrival_time),
    });
}

var curves = [];
for (var i = 0; i < paths.length; i++) {
    if (paths[i].length > 1) {
        var curve = [];
        for (var j = 1; j < paths[i].length; j++) {
            curve.push([
                paths[i][j].time - paths[i][0].time,
                Math.floor((paths[i][j].time - paths[i][j - 1].time) /
                    (paths[i][j].dist - paths[i][j - 1].dist))
            ]);
        }
        curves.push(curve);
    }
}

fs.writeFileSync('curves.json', JSON.stringify(curves));

speed.js

var Canvas = require('canvas'),
    glob = require('glob'),
    fs = require('fs'),
    rainbowDash = require('rainbow-dash'),
    leftpad = require('leftpad'),
    width = 2560,
    height = 1280,
    moment = require('moment'),
    radius = 100,
    c = new Canvas(width, height + 100),
    ctx = c.getContext('2d');

var speeds = JSON.parse(fs.readFileSync('curves.json'));

var hexOut = rainbowDash({ outputFormat: 'hex' }, {
    0: '#0000ff',
    0.5: 'rgb(0,255,0)',
    1: '#ff0000'
});

ctx.fillStyle = '#fff';
ctx.fillRect(0, 0, width, height);

ctx.strokeStyle = hexOut(0);
ctx.globalAlpha = 0.1;
ctx.globalCompositeOperation = 'multiply';

console.log(speeds.length, ' to do');
for (var i = 0; i < speeds.length; i++) {
    if (i % 800 === 0) {
        console.log(i, ' done');
        ctx.strokeStyle = hexOut(i / speeds.length);
    }
    ctx.beginPath();
    for (var x = 0; x < speeds[i].length; x++) {
        ctx.lineTo(~~(speeds[i][x][0] / 2.5), ~~(height - (speeds[i][x][1])));
    }
    ctx.stroke();
}

fs.writeFileSync('speed.png', c.toBuffer());