Fri. Feb 26th, 2021

MOVICHIP

Electronic Solutions for Motorsport

Lap Timer App – Improving GPS Accuracy

3 min read

1 simple tip to improve GPS lap timer app accuracy. GPS receivers in most Android phones, update once a second ie 1hz. This may be fine for navigation apps but for lap timing it can cause some issues.

A lap timer app may use interpolation to get the lap time or it may simply show the lap times as the GPS position is updated.

If the lap timing app simply updates when the GPS location is updated, there is not a lot we can do, however..

If you are using a lap timer app that uses interpolation or an algorithm that predicts the “real” time the phone crosses the line, the following simple tip will increase the accuracy of your lap times.

GPS Algorithm

To “predict” the real time you will cross the line, the app could look at the speed of the vehicle and the distance it has to travel to reach the real GPS point. Which is fine. However the accuracy of this calculation would be affected if the car is accelerating or braking between GPS updates.

We should set the measuring points, (our start, finish and split points) at a position where we will not be accelerating or decelerating rapidly. This will mean setting the measuring points at the apex of corners (or slightly after) or at high speeds** (60mph/100km/h+) where the vehicle will not be accelerating at a high rate like the car would be at low speeds.

**This is going to be dependent on the vehicle. If the vehicle accelerates from 100km/h to 200km/h in 5 seconds then measuring at 200km/h would be better. Generally, the higher the speed the better.

When the speed is relatively constant between GPS updates, the calculation as to when we will cross the line will be more accurate compared to there being a big difference in the speed between GPS updates.

Proviso – G-Sensors

Having said all this, if the GPS lap timing app you are using also makes uses of the phone’s g-sensor then these points could be mute, depending on how good the algorithm is. Because the app is measuring the speed and the deceleration it can anticipate the time the phone will cross the line accurately even if you are accelerating/decelerating assuming the rate of change of speed is constant.

It is key that lap timing apps that use the device’s g-sensor are calibrated properly. This is absolutely essential.

MoviChip Time Trial

Does the MoviChip Time Trial lap timing app use an algorithm? Yes.

We use speed and distance to calculate when the lines will be crossed.

Do we use the g-sensor?

At this time, we do not.

We do not use the g-sensor because the orientation of the device is so critical, and this orientation can change as we go up and down hills and when we go over bumps. We have also found that the signals from g-sensors can also be quite erratic. In short, as the technology stands at the moment, we think the lap timing is more accurate without using the g-sensor.


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