127 lines
4.5 KiB
Markdown
127 lines
4.5 KiB
Markdown
# Advisory Circular
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This is a twitter bot that alerts you when aircraft fly in circles.
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You can see it in action at
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[@SkyCirclesLA](https://twitter.com/SkyCirclesLA).
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The bot uses the adsbexchange.com API to get aircraft data in
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realtime. It uses the Pelias front-end to OpenStreetMap and
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WhosOnFirst data to come up with some color description of the
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aircraft's location. It uses an embedded Chromium browser to take a
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screenshot of the aircraft on the adsbexchange.com "global radar
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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 miles 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. If an aircraft was previously circling, it must be considered
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not-circling for at least 30 minutes before it is again eligible to
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be considered circling.
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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.** See https://github.com/pelias/docker and
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if you're lucky the `projects` folder will have a predefined project
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that covers the area you want. I run one using the `los-angeles-metro`
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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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**Get access keys for a twitter account.** Follow the [instructions at
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botwiki](https://botwiki.org/tutorials/how-to-create-a-twitter-app/).
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## Running the bot
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Put your adsbexchange.com API key and twitter keys in `secrets.yaml`.
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Create an initial history database:
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`echo '{}' > advisory-circular.db`
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Install 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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`node out/script.js --url https://adsbexchange.com/api/aircraft/json --lat <lat> --lon <lon> --radius <radius>;`
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Specify your geographical region of interest by specifying a circle at
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`<lat>`, `<lon>` with a radius of `<radius>` miles.
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The bot will run once. The adsbexchange.com API only provides
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instantaneous positions, so the bot will have to run many times and
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collect some history before it's able to detect any circles.
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```
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while :
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do
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node out/script.js --url https://adsbexchange.com/api/aircraft/json --lat <lat> --lon <lon> --radius <radius>
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sleep 10
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done
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```
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* **Do not run the script with a large radius, or adsbexchange.com will
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ban your IP.** I use a radius of 40 miles.
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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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## To do
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- [ ] If we don't have neighbourhood or locality (just county), try to
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use the locality of a nearby venue. E.g. "2 miles from
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Glendale."
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- [ ] Solve the issue of needing a differently sized buffer zone for
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different airports--2 miles distance from LAX is still
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practically inside the aiport. Add list with custom airport
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coords and radii? Get access to OSM polygons and compute our own
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distances?
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- [ ] Add type information to tweet status, e.g. "Eurocopter AS350".
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- [ ] Lookup registration info. Possible sources: FAA,
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adsbexchange.com, janky-ass basestation.sqb's that have been
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passed around for a decade.
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- [ ] Find a source of aircraft images we can use.
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- [ ] Use Wikipedia graph to rank landmarks? More inbound links to a
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page means it has higher significance?
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- [ ] Add support for Mastodon/ActivityPub.
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- [ ] Generate our own maps instead of using adsbx's? The adsbx map
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isn't always in sync with the data from the API.
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- [ ] Run at global scale!
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