aprs.fi as a source of GPS tracks

I have some friends who track their positions via ham radio on APRS. Cool stuff. The site http//aprs.fi/ has a really nice map viewer of the data. I’m looking at extracting that data for my flight tracker.

The easy way is to have the user use the data export tool to download a file. It’s a bit awkward and manual but easy to understand. There are multiple format options, CSV seems sufficient. Fields are:

  • time: full text UTC, “when the target first reported this (current) position”
  • lasttime: identical to time in my data. “the time when the target last reported this (current) position”
  • lat: decimal degrees
  • lng: decimal degrees
  • speed: kilometers / hour
  • course: degrees, probably true?
  • altitude: meters
  • comment: empty in my examples. “APRS comment”

aprs.fi also has a simple REST API. Unfortunately it only seems to report the last fix, not a history of the track. A fetch of the last location works like http://api.aprs.fi/api/get?name=CALLSIGN&what=loc&format-JSON&apikey=KEY.

The granularity of track data is up to the APRS sender. I think one fix every 5 seconds is considered fast. My friend’s tracker is smart enough to send more rapid updates when turning, etc. 66 points for a 90 minute flight.

There are other sources of this data. aprs.fi notes you can also get the data directly from APRS-IS via a library like Ham-APRS-FAP. There’s also aprsworld.com; Adam Fast has some nice API code that relies on his having database access to aprsworld.