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Hardware / LapTimingGuide

“Real time” lap timing with Race Technology equipment – a complete guide

Note that all the information contained with this guide to lap timing is included elsewhere, including in individual product manuals and the relevant parts of the knowledge base, however we’ve had a number of customer requests to bring all the information relevant to lap timing together into a single place, and list some of the most common mistakes, misunderstandings and “gotchas”! This is an introductory guide, for more detailed information about most items, it is required to follow the links from this page.

Race Technology equipment relies on GPS rather than the older lap beacon method.

There is no way for the equipment to automatically “know” where laps and sectors start and finish, so this information has to be set by the user. Timing points on the track are called “track markers” in the software and elsewhere in this documentation. A track marker can be thought of as a virtual optical beacon that can be added anywhere on the circuit. There are 2 ways that track markers can be setup:

  1. If you have already been to the track and have logged a run file, or you have access to a run file from another source, then you can add track markers in the analysis software, from the track map tool (more information). The track markers can then be save to a file and used whilst driving on the track (more information)
  2. If you have a Race Technology dashboard in the car and connected to the data logger then it is possible to add track markers whilst on the track.

DL1, DL2 and VIDEO4 are capable of calculating lap timing information. For the rest of this guide, we refer to DL1 only – however the same information applies to the DL2 as well.

With regards displaying results, as well as the DASH1, DASH2 and DASH3 being able to display lap timing results, the VIDEO4 can display lap timing information on its real time overlay. Note that if you have both a DL1 and a VIDEO4 in your system, then it is the VIDEO4 that does all the lap timing, the DL1 is there just to supply raw GPS data.

Typically we recommend that the user adds the track markers in the software, and then saves them.

How does the lap timing work?

If you understand how the lap timing system works using GPS then it helps avoid most of the common mistakes.

Firstly to calculate lap times, it’s not practical to simply define a single point on the track as the chance of crossing the exact same point on the track again is very small. Instead each track marker defines a line on the track. To trigger the lap timing the vehicle needs to cross this line in the correct direction.

When we add a track marker (either by pressing a button on the dash whilst racing, or from the analysis software) we save 2 pieces of information about it:

  • The centre coordinates of the track marker, NOT the end points
  • The current direction of travel

This information is then used to draw a virtual line across the track, and every time the vehicle crosses this line, we get a new timing result. One important question is how close to the centre point of the track marker does the vehicle have to pass to trigger the lap timing? The answer depends on the application:

  • If the DL1 is doing the lap timing, then for firmware versions up to and including version 31, it is approximately 22m. For firmware versions 32 and after, it is approximately 44m, ie a total marker "width" of 88m. This distance was increased in later firmware versions as some customers found that the lap timing was not always getting triggered reliably. If you see unreliable lap timing results then upgrading to the later DL1 firmware is strongly recommended.
  • If the VIDEO4 is doing the lap timing then the width of the track marker is also approximately 88m
  • Note that in the case of the analysis software the width of the lap marker - as displayed by Analysis - is user defined under “lap and sector options” -> “options” -> “length of automatically added markers”. When you load a lap file, the centre point of the track marker is taken and the information from “lap and sector options” used to calculate the width of the track marker. Note that this width setting only affects the width as displayed and used in Analysis, it does NOT affect the nominal 88m width used by current DL1, DL2 and VIDEO4 firmware - which is what controls in-car lap timing.

Whether you are using a DL1 or a VIDEO4 to do the lap timing the maximum number of track markers that can be used for real time lap timing is 12. If you save any more than 12 in a lap file the later ones are simply ignored.

Also note that if you set up names for track markers, then this information is not stored in the lap file.

When talking about GPS based lap timing there are 2 questions that commonly come up:

  1. If we are using GPS data with, let’s say a 10Hz update rate, doesn’t that mean that the lap times are only accurate to 1/10th of a second. The answer to this one is certainly “no”, the time that the vehicle crosses the line is worked out internally to a very high precision by looking at the 2 GPS samples either side of the crossing point and working out at exactly what time is was crossed.
  2. The other question is simply “how accurate is lap timing based on GPS”. The answer to this one is that it depends on the GPS data. For example is there is a very typical 1-2m of error on the GPS data, and the vehicle is moving down the straight at about 100mph, then the error would apparently be about 0.02seconds-0.04seconds. However, in practice whilst the GPS accuracy is typically 1-2m, the error in GPS position only changes (or “drifts about”) quite slowly, typically over the period of 10s of minutes. As a result, if we assume a typical lap time of just a few minutes or less, the error in 1 lap compared to the previous lap is normally much better than 1-2m. That is the theory… in practice if you compare our GPS based lap times with those from an optical beacon system (which have a beam spread of >1m) then the accuracies are directly comparable at “a few 100ths of a second”.

Overview of the rest of the guide

Subsequent sections further explain lap timing related activities.

This section describes how to define track markers using the Analysis software and then transferring them onto the memory card using LAP files.
This section descrbies how to define track markers from any of RTs dashboard products whilst on the track.
Contains informaiton on connecting DL1, VIDEO4, and DASHx together and configuring them to calculate and display lap times correctly.
Contains informaiton on connecting DL1 and DASHx together and configuring them to calculate and display lap times correctly.
Lists most common errors to avoid when doing lap timing
Page last modified on January 22, 2015, at 12:52 PM