161 lines
5.6 KiB
Markdown
161 lines
5.6 KiB
Markdown
# Advisory Circular
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Advisory Circular is a twitter bot that tweets when it detects
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aircraft flying in circles.
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The bot uses data from the [ADS-B
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Exchange](https://adsbexchange.com/), which is a network of amateurs
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who track aircraft, to monitor all the aircraft flying in a particular
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geographic region. When it detects a
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[helicopter](https://twitter.com/SkyCirclesLA/status/1224376709048193024),
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[fixed wing
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aircraft](https://twitter.com/SkyCirclesDC/status/1223995896536240133),
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[blimp](https://twitter.com/SkyCirclesLA/status/1213310909302493184),
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or
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[autogyro](https://twitter.com/SkyCirclesLA/status/1216464781869121536)
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flying in circles, it will tweet a short description of the aircraft
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and an image of the aircraft's track on a map.
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The text of the tweet includes the aircraft's registration (if known,
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otherwise just its ICAO code), type, speed, altitude, and transponder
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squawk code. It will also include the city over which the aircraft is
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circling, and a nearby landmark—a park, school, restaurant, or some
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other notable place.
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The bot takes a screenshot of the aircraft as it currently appears on
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the ADS-B Exchange's "Global Radar View" web page.
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This code currently powers the following bots:
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* [@SkyCirclesLA](https://twitter.com/SkyCirclesLA), which covers
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the Los Angeles metro area.
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* [@SkyCirclesSF](https://twitter.com/SkyCirclesSF), the San
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Francisco Bay area.
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* [@SkyCirclesDC](https://twitter.com/SkyCirclesDC), for the
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Washington D.C. area.
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## Technologies used
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This bot is written in Clojurescript, targeting Node.
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The bot uses the [ADS-B Exchange
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API](https://www.adsbexchange.com/data/) to get aircraft data in real
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time.
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It uses the [Pelias](https://pelias.io/) front-end to OpenStreetMap
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and WhosOnFirst data to come up with some color description of the
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aircraft's location.
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It uses an embedded Chromium browser to take a screenshot of the
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aircraft on the ADS-B Exchange "global Radar View".
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## Criteria for tweeting
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The bot will consider an aircraft to be "circling" if:
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1. In the past 25 minutes, the sum of the aircraft's bearing changes
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is more than 1440 degrees. Port turns cancel out starboard turns
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and vice versa--there needs to be a net change of at least 1440
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degrees in one direction.
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2. The centroid of the last 3 minutes worth of positions must be more
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than 2.5 km away from all known airports.
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3. The centroid must be located within the county of Los Angeles.
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(This is just because I don't yet have airport data outside Los
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Angeles County.)
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4. The aircraft must, at the moment of decision, be at an altitude of
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300 feet or more.
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5. Once an aircraft is considered to be circling, it will be tweeted
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about. It won't be eligible to be considered circling/tweeted about
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again until it stops circling and 30 minutes pass.
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Many of the specific numbers in the above criteria can be customized
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on a per-bot basis.
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There are a lot of weird flight paths that can meet criterion #1, and
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I kind of like it that way. For example, see
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https://twitter.com/lemonodor/status/1203033917483175936 (consider
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whether we also want to detect something like
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https://twitter.com/lemonodor/status/1204550831103590400).
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## Prerequisites to running the bot
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**Set up a Pelias instance containing information for the geographical
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area you're interested in.** Pelias is the geographic database that
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the bot uses to know which city aircraft are circling over and find
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nearby landmarks. It's also used to filter out aircraft that are
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circling over airports. See https://github.com/pelias/docker and if
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you're lucky the `projects` folder will have a predefined project that
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covers the area you want. I run one using the `north-america` project.
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**Get an API key for adsbexchange.com.** See
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https://www.adsbexchange.com/data/. If you have a receiver and feed
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them data, they'll give you a key for free. Alternately, find another
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data source of realtime (or not) aircraft data and massage it into a
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form that the bot can work with.
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**Create a twitter account and get app access keys for it.** Follow the [instructions at
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botwiki](https://botwiki.org/tutorials/how-to-create-a-twitter-app/).
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**Get a `basestation.sqb` file.** `basestation.sqb` is a crowdsourced
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sqlite database file that contains registration and type information
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on aircraft. There is no canonical or official version of this file,
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unfortunately. Honestly, it's a real mess that somehow many people in
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the planetracking hobby are convinced is a good thing, or at least not
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a problem. In any case, you can try downloading a version from
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http://www.kinetic.co.uk/resourcesdownloads.php#4.
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## Running the bot
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Put your ADS-B Exchange API key and twitter keys in `secrets.yaml`.
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Create a `config.yaml` that looks like this:
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```yaml
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adsbx:
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url: https://adsbexchange.com/api/aircraft/json
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pelias:
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url: http://<my pelias host>:4000/v1
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lat: 34.1335
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lon: -118.1924
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radius-km: 10
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basestation-sqb: clean-basestation.sqb
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```
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Create an initial history database:
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`echo '{}' > advisory-circular.db`
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Make sure you have at least Node version 10.0.0 installed, and then
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install the node dependencies:
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`npm install`
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Compile the clojurescript:
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`npx shadow-cljs compile script`
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Run the bot:
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```
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while :; do python intervalexec.py 10 node out/script.js; sleep 5; done
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```
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`intervalexec.py` is a script that will try to run the bot script no
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more than once every 10 seconds.
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* **Do not run the script with a large radius, or adsbexchange.com will
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ban your IP.**
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* **Do not run the script more ofen than once every 10 seconds, or
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adsbexchange.com will ban your IP.**
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