GPS Distance, Speed Vs Vehicle Odometer, Speedometer

Which is correct?

Almost all Vehicle tracking systems today, displays the Odometer & Speed of the vehicle. Most of these systems make use of GPS hardware to calculate Speed and Distance travelled by the vehicle. But, often these values differ from what?s shown on the Vehicle?s dashboard!

Which is Correct? GPS or Vehicle Dashboard?

To get a right answer to this question, we need to understand how these values are calculated by each device.

How traditional odometer works?

Most odometers found in vehicles are either electronic & mechanical. Mechanical ones work on the principle of gear train with an incredible gear ratio. These mechanical odometers were dependent on timely calibration and also had much non-linear errors. Recently, almost all the odometers you see in vehicles are electronic ones with digital displays. Electronic odometers work on the same principle but using a magnetic pick up sensor to sense the wheel rotations, eventually applying the ratio to derive distance travelled. Though the errors are less in electronic odometers compared to mechanical ones, there is still substantial error ranging from 3% to 6% and dependent on regular calibration. Regular calibration of the odometer is a way to reduce the errors, but practically difficult to practice!

How GPS based odometer works?

GPS based odometers work by calculating the hemisphere distance travelled between two co-ordinates. Though this calculation can give very accurate results, the accuracy depends on lot of factors such as, accuracy of the GPS hardware module, Sample rate for the calculation and consideration of Altitude, HDOP & PDOP parameters received by GPS receiver. Many low end mobile phones suffer in accuracy because of this and so are many cheap GPS Vehicle Trackers. So, if you are very particular about the Distance travelled & Speed values, you must choose the right GPS Trackers.

Conclusion

Provided you chose the right hardware, we recommend GPS based odometer over other factory fitted odometers, as it doesn?t require regular maintenance and re-calibrations, which make effective fleet management practical and easy!