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| Re: BusTime/GPS (349508) | |||
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Re: BusTime/GPS |
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Posted by Stephen Bauman on Mon Sep 16 23:09:51 2024, in response to BusTime/GPS, posted by BusRider on Mon Sep 16 22:34:40 2024. There are several problems with using the MTA's vehicle position GTFS-RT bus feed for precise or instantaneous display.First, new data for a particular bus is updated every 30 seconds. There's a delay in the feed - which can be partially corrected. The feed itself is updated every 15 seconds. This means there are duplicate entries for a particular bus. Second, there is no update if the bus has not moved. Thus, you are on the lookout for missing updates to determine the bus has not moved - either traffic or at a bus stop. Third, there is confusion about the position for the first and last stops. The trip may end far enough from the stop to be recorded. There's a similar problem with the start. Fourth, there is some trouble identifying the route and position along the route from the feed. There is a vehicle id with the feed. The route has to be inferred from the lat/lon position history. I don't know how they take the raw data from the GTFS-RT feed and place it on a map. Assume a bus is traveling at 20 mph or 0.67 mile per minute. There's the built in 30 second uncertainty regarding the position vs. the time it's received. That accounts for 0.33 miles. |
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