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Coloring Transit GPS Tracks by Azimuth

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I’ve been spending today getting pretty seriously turned on by more than 400,000 transit GPS tracks colored according to their azimuth (measured from start and end points). Beside being pretty, it ends up being a stupendously good way to differentiate tracks which otherwise run quite close together.

Would anyone be interested in prints if I were to make some?

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Posted in: Design | Maps
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Making tracks

Here are some early results from my efforts to track transit vehicles, these ones in Toronto:

ttc-early-tracks

It looks like a crude system map, and it is, but it’s actually made of thousands of vehicle GPS tracks.

The vehicle tracks are oddly pretty; I keep wasting time just zooming in on different spots as new tracks are added. Here’s a transfer point at one of the subway stations:

transit station

Bus stops shown as ~20m circles

And what looks like perhaps a train station or a bus garage, below. This image also shows the relative frequency of service on different streets, something that becomes quite visible in the data when the lines are given a high degree of transparency.

bus garage?

Buildings for scale

And here’s an expressway carrying some limited-stop services:

expresswayAs of now, after just a week of  erratic development and testing, I’ve collected ~60,000 unique tracks, representing ~160 scheduled lines, derived from 3,200,000+ vehicle location records. About 50 new vehicle locations come in each second that I have my little script running.

Here’s what I’m doing so far, described algorithmically here, and implemented in a Python script:

A track is a set of ordered points, each point with a position and a time. The next step is to line the tracks up with the stop segments to which they’re scheduled, and if they’re actually close and the direction matches, to calculate stop times and segment durations from the observations. That’s actually turning out to be pretty difficult, but I’m sure I’ll crack it fairly soon. One thing I’ll have to seriously consider as I’m doing this is error in the location reports.

downtown signal degredationAs the first image and the one immediately above show, there is significant error in the data, particularly downtown where tall buildings are presumably interfering with GPS signal reception.

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Posted in: Data
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