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.
