Support Document
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GPS Precision Summary
Support Document
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GPS involves calculating four unknown values: latitude, longitude, altitude, and time. This means we need to track at least four different satellites to solve this problem and determine an estimated position. The signals from the satellites must be received with sufficient quality to calculate the position.
GO® Telematics Device GPS Precision Summary
How the GO Telematics Device Evaluates GPS Coordinates
A GO telematics device obtains latitude, longitude, altitude, and speed coordinates (“GPS Coordinates”) directly from the applicable GPS chipset (“GPS Chipset”) embedded in the GO telematics device. In order for GPS Coordinates to be considered valid by Geotab, the following conditions must apply:
- A latitude, longitude, and altitude (commonly referred to as “3D” in GPS terminology) fix using at least four (4) satellites.
- A GO telematics device requires a minimum of four (4) satellites to be tracked by the GO telematics device for a GPS record to be valid.
- A GPS record containing the GPS Coordinates is marked by Geotab as not valid if it does not meet this requirement.
- The position dilution of precision (PDOP) needs to be six (6) or less.
- This PDOP threshold is programmed into the GPS Chipset by Geotab. A lower PDOP value indicates a more accurate GPS reading (i.e. a PDOP of 1 would be considered a more accurate GPS reading than a PDOP of 2, etc.)
- A GPS record containing the GPS Coordinates is marked by Geotab as not valid if it does not meet this requirement.
- The time dilution of precision (TDOgnssP) needs to be 10 or less.
- TDOP relates to the synchronization between the GPS Chipset receiver’s time and the satellite time. This threshold is programmed into the GPS Chipset by Geotab.
- A GPS record containing the GPS Coordinates is marked by Geotab as not valid if it does not meet this requirement.
- The Speed Accuracy Estimate needs to be within one (1) meter per second (m/s).
- The GPS Chipset sends an estimate of the speed accuracy; contained in the GPS Coordinates.
- A GPS record containing the GPS Coordinates is marked as not valid by Geotab if it does not meet this requirement.
- GPS Coordinates must not have a speed increase of over 30 km/h (18.64 mph) from the previous GPS Coordinates.
- A GPS record containing the GPS Coordinates is marked as not valid by Geotab if it does not meet this requirement.
Chipset Specification — Circular Error Probable (CEP) Accuracy
GO9 (Hardware version E1 or higher) / GO9B (all versions) | GO9 (Hardware version D3 or lower) |
1.5 meters with SBAS(1) | 2.5 meters with SBAS |
Chipset Specification — Tracking Sensitivity
GO9 (Hardware version E1 or higher) / GO9B (all versions) | GO9 (Hardware version D3 or lower) |
-167dBm(2) | -167dBm(2) |
Chipset Specification — Acquisition Sensitivity
GO9 (Hardware version E1 or higher) / GO9B (all versions) | GO9 (Hardware version D3 or lower) |
-148dBm(2) | -148dBm(2) |
Note:
- SBAS (Satellite-based augmentation system) are region-specific satellite constellations that transmit data used to correct errors in GPS signals
- GPS + GLONASS + Galileo + Beidou
