Geotab Fleet Management System - Accuracy GPS System

A generic GPS device would use PDOP, VDOP and HDOP which are different measurements for dilution of precision (positional, vertical and horizontal).

In the case of a GO device the criteria for a valid GPS latch is a bit different mainly because a GO device receives a number of other measurement data.

Below is the list criteria that would need to be satisfied in order for a GPS latch to be considered valid. This algorithm is stored in the device firmware locally and therefore is not stored in any table, the only thing we store in a table is if the GPS latch received is Valid or Invalid.

  • 3D fix (min. 4 SVs)
  • Position DOP mask needs to be 10 or better (on LEA4) / 6 or better (on LEA5)
  • Time DOP mask needs to be 10 or better
  • Speed Accuracy estimate needs to be better than 1m/s
  • Ignore first valid.
  • Ignore data that has a speed increase over 30km/h from the previous data.

Notes:

  • Each bit of latitude and longitude has a precision of 0.0000256 of a degree
  • If you do the math 0.0000256 degrees works out to roughly 2.85 meters. This is a rough calculating because converting degrees to meters assumes the earth is a perfect sphere.

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