Quote:
Originally Posted by CSG Mike
HLT without external GPS is a 1hz unit, which gives it a +- 1S range.
|
This is not the way GPS based lap timers work. They use the last position received before, and the first position behind start / finish and interpolate the time and position the line has been crossed using "interpolation". For cars crossing a typical start / finish at around 200 km/h, this interpolation introduces a very small error. This in turn means the receiver update rate has a pretty small influence on timing accuracy, while *position accuracy* has a strong effect. Or in other words: a 1 Hz device delivering 2 meter accuracy will generate a higher timing accuracy than a 5 Hz device at 10 meter position accuracy for most cases.
High update rates are good to get a better understanding of line driven, breaking points etc, and is better in catching speed peaks. The influence on timing accuracy is small but increases for low speed vehicles (e.g. karts).
In case Harry's LapTimer delivers accuracy below 0.05 seconds mostly, this is due to bad accuracy and can be improved by choosing a better mounting position for the smartphone. The most frequent problem is when the smartphone is placed in your cloth, a glove box, or on the co-driver's seat (or in his/her hands). So please always mount your smartphone on the center of your windscreen.
I do not want to post external links in my first post. In case you want further details, please ask.
Quote:
Originally Posted by CSG Mike
Although the lap times are often close, watch the "speedometer" and you'll realize how lacking 1hz really is.
|
This is a general limitation when watching GPS data in real time. GPS speed delivered is outdated when calculated in the sensor already. This is due to signal transmission times as well as processing time. This is typically around 1 second. In addition, a latency is introduced by the update rate (0.5 seconds in average for a 1 Hz device and e.g. 0.025 seconds for a 20 Hz GPS). Finally, low position accuracy will result in stronger smoothing of data (to receive noise), so additional latency is often a signal for bad accuracy too.
The latency in this real time scenario has no influence on recording accuracy! It is always performed on complete information somewhat in the past. You will see this when a lap timer starts a lap late and stops it late again.
I hope that helps,
Harry