Ask HN: How does the FlightRadar's mobile app work?

[krat0sprakhar]

Flightradar[0] is a pretty cool service which has a live map of airline traffic throughout the world. The mobile app has a feature of being able to identify the exact flight name by just pointing your phone at the sky. When you point to the sky, you are asked to calibrate by rotating the device multiple times while keeping the focus on the plane [1]

While I understand how FlightRadar works, with just my GPS coordinates how does the app correctly identify the plane that I'm pointing to? Basically, how does it get the direction I'm pointing towards to narrow down the list of planes that are flying within K miles of a given lat, long coordinate?

[0] - http://www.flightradar24.com/

[1] - http://youtu.be/IqFx77WeYL8?t=4m27s

[lutusp]

> While I understand how FlightRadar works, with just my GPS coordinates how does the app correctly identify the plane that I'm pointing to?

Your device has a magnetic compass. The reason for rotating the device is to calibrate the compass, which relies on a Hall Effect sensor which isn't always accurate until it's been rotated in Earth's magnetic field.

At the end of the process, the device has a geographic position and a reliable compass bearing. It uses this information to draw a vector, and with any luck there's only one plane within the confines of the vector.

[krat0sprakhar → lutusp]

Thanks for the explanation (and the Hall Effect).

[jacquesm]

http://en.wikipedia.org/wiki/Fluxgate_compass

You can make one yourself.

Solid state version:

http://www.google.com/patents/US5241270

[opless]

It doesn't. (Just use GPS)

It uses the magnetometer (and/or a combination of other motion sensors) to determine the direction the camera is pointing at.

Pretty much the same way as Google's street view and sky map apps work. (If you want to research further)

[krat0sprakhar → opless]

Had no clue about Magnetometer! Thanks a lot :)