GPS (Global Positioning System) geolocation is a satellite-based positioning system that determines geographic coordinates (latitude, longitude, altitude) of a receiver with an accuracy of a few meters. Modern smartphones actually combine several satellite constellations (known as GNSS), which improves accuracy. FizziQ uses this receiver to record position, altitude and speed during a movement.
Discover FizziQ
How to measure it in class
FizziQ displays five measurements from the GPS receiver: latitude, longitude, altitude, speed of movement and the estimated accuracy of the position, in metres. The latter allows discussing the reliability of each measurement, an essential practice in experimental science.
Steps:
- Open FizziQ and select the instruments “Latitude”, “Longitude” or “GPS Speed”
- Move around and observe coordinate variations
- Check the “GPS accuracy” reading and compare its value indoors, near a window and outdoors
- Measure walking, running, cycling speed
- Record a route and calculate the total distance
- Compare GPS speed with a stopwatch measurement
Scientific activities on this topic
- Uniform linear motion
- Climb rate during a flight
- Variation of g with latitude
- Measuring travel speed
Learn more
Operating principle:
- At least 4 satellites send their position and transmission time
- The receiver measures the signal travel time
- Knowing the speed of light, it calculates the distance to each satellite
- By trilateration, it determines its position
Precision:
| Condition | Horizontal precision |
|---|---|
| Clear sky | 3-5 m |
| Urban area | 10-20 m |
| Indoor | Not functional |
| With GLONASS/Galileo | 2-3 m |
| Differential (DGPS) | < 1 m |
Update rate: the GPS receiver of a smartphone typically delivers one position per second, a much slower rate than the accelerometer or the gyroscope. GPS therefore suits movements lasting several seconds or minutes (walking, running, cycling), not fast phenomena.
Complete system (GNSS):
Modern smartphones use multiple constellations, each counting a few dozen satellites:
- GPS (United States)
- GLONASS (Russia)
- Galileo (Europe)
- BeiDou (China)
Formula
Distance between two nearby GPS points (flat-plane approximation, valid for small separations):
d approximately equals R times square root of [(Delta lambda times cos(phi)) squared + Delta phi squared]
where:
- d: distance (m)
- R = 6,371,000 m: Earth radius
- Delta lambda: longitude difference (rad)
- Delta phi: latitude difference (rad)
- phi: average latitude (rad)
GPS speed: v = d / Delta t
Application examples
- Navigation applications (Waze, Google Maps)
- Sports activity tracking (Strava)
- Geocaches and scavenger hunts
- Precision agriculture
- Vehicle fleet tracking
FAQ
Q: Why does GPS not work indoors? A: Satellite signals are very weak and do not pass through walls. Indoors, the smartphone uses Wi-Fi, Bluetooth, and cellular antennas for approximate location.
Q: How to measure speed with FizziQ? A: The “GPS Speed” instrument calculates speed from position variations. You need to be moving for a reliable measurement.
Q: Does GPS consume a lot of battery? A: Yes, it is one of the most power-hungry sensors. FizziQ allows choosing the sampling frequency.
Q: What is the accuracy of GPS altitude? A: Less accurate than horizontal: plus or minus 10-20 m. The smartphone barometer is often more accurate for small altitude variations.
Related concepts
GPS speed - GPS altimeter - Latitude - Longitude - Trilateration - Navigation