Where the Heck Am I? Understanding and Managing Location in Your Application
summary
Explains exactly how satellite positioning computes a fix: 4 satellites for trilateration, atomic-clock timing corrected by relativity (a 35 µs/day offset would otherwise add ~11 km/day), and use of ephemeris and almanac data (almanac download = 12.5 minutes unless assisted via the internet). Reports practical accuracy ~5 m in ideal conditions, lists major error sources: ionosphere, multipath, occlusion, and notes alternatives and improvements — GLONASS, Galileo, cell/Wi‑Fi, and the Android GNSS Measurement API for raw measurements.
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chapters (18)
- 0:00Introduction and context
- 4:21Why location matters
- 6:48GPS origin and history
- 9:59Understanding latitude and longitude
- 13:30How apps get location data
- 14:55How GPS satellites work
- 17:45Trilateration in 3D space
- 21:18Satellite signals and data
- 24:26Assisted GPS and cold/warm fixes
- 25:49Calculating distance to satellites
- 28:38Why four satellites are needed
- 29:44GPS accuracy limitations
- 30:04Relativity and GPS clocks
- 32:33Ionosphere and signal errors
- 33:16Multipath errors and reflections
- 33:58Other positioning systems
- 35:47Hardware vs software calculations
- 36:51Q&A
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