Versatile Bio Sensor Guide: GPS

Understanding the global positioning system sensor on the Versatile Bio

What it measures:

The global positioning system (GPS) measures the global coordinates of the participant in latitude and longitude, plus the speed and elevation.  The sensor works similar to the GPS component in your phone, only in this case it is synchronized with other Versatile Bio recording sensors. 

Research Applications:

Way-finding, outdoor market research, studies in driving, sports, logistics, professional performance, etc. 

How to use:

The GPS sensor reads the signal from the global position system satellites and must be used in a place where the signal is not blocked.  

The sensor will not work well if excessively shielded by buildings or other structures.  When starting up (cold start), it may take the GPS system up to 38 seconds to acquire a signal.

Place the GPS sensor on the surface to be tracked.  The side marked "UP" must be oriented upwards.

Connector on Versatile Bio:

Digital AUX Input

Visualization filters:

A data visualization filter is not necessary for GPS.  You will have to reduce the data scale for the GPS channel until you see a signal. 

Data file:


The GPS system reports the following:

  • Channel 1:  Latitude
  • Channel 2:  Longitude
  • Channel 3:  Number of tracked satellites
  • Channel 4:  Elevation
  • Channel 5:  Speed
  • Channel 6:  Flag
  • Channel 7:  Horizontal Position Accuracy (HDOP)
  • Channel 8:  UTC


Latitude and Longitude:

  • Latitude is presented in degrees with a range of ±90.  For example, 42.348260 is at 42.348260 degrees N, or 42°20’53.74″N.
  • Longitude is presented in degrees with a range of ±180. For example, -71.088193 is at 71.088193 degrees W, or 71°05’17.49″W

Number of Satellites

  • This is the number of satellites providing location data to the GPS system.  The ideal number for proper function is 4.  Below this number, the system will be imprecise (especially in reported speed and altitude values).

Elevation
  • This is the elevation in meters above sea level.

Speed

  • This is the speed of the GPS sensor in Km/h
  • The maximum track-able speed by the system is 255.9 Km/h

Flag

  • This is a number reflecting the state of the GPS sensor for this particular sample of data.
  • The number means the following:
    • 0:  No valid data
    • 1:  Valid data
    • 2:  Valid data, GPS in Standard Positioning System (SPS) mode, expected error between 0.7 and 3 meters
    • 3:  Valid data, GPS in Precise Positioning Service (PPS) mode, expected error between 0.5 and 2 meters
    • 4:  Valid data, Real Time Kinematic (RTK) mode, not implemented here
    • 5:  Valid data, Float RTK mode, not implemented here 
    • 6:  Valid data, position estimated (dead calculation):  the position is calculated with poor precision or can't be calculated at all and is now estimated based on last valid received data and other integrated sensors
    • 7:  Not implemented here
    • 8:  Not implemented here
    • 9:  Repeated data flag (added by Bitbrain): marks that no new data has been received for this sample, so the previous valid entry has been repeated. 

Horizontal Dilution of Precision (HDOP)

  • This 8-bit number represents the precision quality based on the satellite position relative to the GPS device.
  • The following can be used to evaluate tracking quality:
    • <1:  Ideal
    • 1-2:  Excellent
    • 2-5:  Good
    • 5-10:  Moderate
    • 10-20:  Fair
    • >20:  Poor

Coordinated Universal Time (UTC)

  • This is UTC time.
  • The output must be divided by 10, then the format will be HHMMSS.S  (hours, minutes, seconds)
  • Note that UTC output may be correct even if the Flag reports 0: no valid data