Measure lap times with Racelogic GPS technology

dear all,

since the year 2000, a movement profile of a fast-moving vehicle can be recorded with high accuracy using GPS. Prerequisite: fast and very good GPS engines that can filter signal noise and the best mathematical knowledge for the calculation of the main variables speed and heading and the data to be derived from them.

The #GPS - #Global #Positioning #System - is a #31 #NAVSTAR satellite based system developed and operated by the #US Department of Defense. The official designation is "#Navigational #Satellite #Timing and #Ranging - #Global #Positioning #System" (#NAVSTAR GPS ).

#NAVSTAR is also sometimes used as an abbreviation for "Navigation System using Timing and Ranging". GPS officially went live on July 17, 1995.

GPS has also been working for civil use since 1995: in all weather conditions, anywhere in the world and 24 hours a day. Since the year 2000, #Selected #Availability (artificial #signal degradation) has been deactivated and GPS has since been used to accurately measure #vehicle movements.

Each of the NAVSTAR satellites has an #atomic clock on board and if you receive GPS signals from at least three satellites, a GPS receiver can determine the distances between your position and the satellites. The classic #GPS receiver now calculates its position through #triangulation.

That means: The position is updated at least every 1/10 s. This would already result in a high #accuracy when capturing a fast-moving object. But the raw #position detection every 1/10 s is not enough to achieve the really necessary #accuracies.

Increased relative positional accuracy from CEP 3 m stationary to CEP <1 m when moving.


Calculation by the Doppler effect.

If you were to calculate the speed of a vehicle solely from the raw position change, then you would have too much #noise in the signal.

When the #receiver moves relative to the #satellites, there is a shift in the #signals (change in frequency), the Doppler effect, and the Racelogic systems now calculate the speed from these minimal changes - and all further calculations are based on this.

The direction of movement (heading) of the receiver is also determined and can be used as an artificial #compass or to align #electronic maps.

From the speed and heading data, Racelogic measuring systems then mathematically derive all other driving dynamics data such as #longitudinal and #lateral acceleration, #curve radius, #elevation profile, relative #position on the #route and #yaw rate. #Kalman filters ensure an additional #reduction of #noise in every #measurement process - but hardly reduce the #responsiveness.

The #movement dynamics are not overly smoothed. This is how the typical "fine-jagged" graphs for speed and g-forces are created - a quality feature for open and fast #GPS data recording. For data analysis, individual #smoothing options are available in the software for easier analysis.

Conclusion: the measurement with the #technology used by Racelogic achieves excellent accuracy when calculating #driving dynamics data.

Many years of experience with GPS data from the field of automotive development (systems such as #VBOX 3i up to 100 Hz clocking and inertial correction) allow Racelogic to record the realistic driving dynamics very accurately, even with systems clocked below 20 Hz.


For cost reasons, #GPS receivers that are suitable for #motorsport use can only be found in real #measurement systems. GPS receivers of mobile phones, navigation systems or tracking systems (e.g. trucks/logistics tracking) are fundamentally unable to realistically record the movement of racing vehicles or "dynamically" moving objects in general. They are neither responsive enough, nor do they have a sufficient sampling rate for realistic speed and direction information, and they usually smooth the data to a great extent.

Detailed knowledge.

GPS is based on 31 satellites (effectively 24), which constantly broadcast their current #position and the exact time with coded #radio signals. High-quality GPS receivers can then calculate their own #position and #speed from the #signal propagation times. Theoretically, the signals from #three #satellites are sufficient, which must be above their #cutoff angle, since the exact position and height can be determined from them.

GPS receivers do not have a clock that is accurate enough to correctly measure transit times. Therefore, the signal of a fourth satellite is actually required, with which the exact time can then be determined in the receiver.

Due to the relativistic time effects occurring in high orbits of the satellites (average altitude 20,200 km) (lower gravity means that time on board the satellites runs faster than on the earth's surface) are taken into account. There is hardly any atmospheric disturbance that distorts GPS signals, but the #ionosphere changes the #signal waves - even this expected #deceleration is already taken into account by very good #GPS receivers. All #GPS engines used by Racelogic use the code + carrier phase #measurement method with reduced signal noise.

Why is the GPS antenna installation really only correct on the vehicle roof?

In the #frequency ranges used, the #electromagnetic radiation propagates in a straight line, similar to visible light, but is not affected by clouds or precipitation (exception: strong #freezing rain, which can cause #multipathing effects). Nevertheless, due to the low #transmission power of the GPS satellites, a direct line of sight to at least 4 satellites is required for the best reception of the signals. The typical cut-off level of <10° prevents signals from being received from satellites when they are too low on the horizon.

Proper antenna mounting reduces signal noise and increases accuracy.

Signals that are reflected multiple times (multipathing effects) can also lead to #inaccuracies between high buildings or near the #box buildings if the line of sight to the satellites is frequently interrupted.

In addition, there are also difficulties with unfavorable #satellite constellations, for example if only three satellites close together are available from one direction for #position calculation.

For an exact position determination, 4 satellite signals from different directions should be receivable.

From this follows:
Especially on #topographically difficult #tracks such as #Nordschleife and #Spa, the antenna must be mounted as horizontally as possible and ideally in the middle of the roof.

Typical mistakes - unfortunately still often seen in racing:


In particular, mounting a GPS antenna (which is intended for outdoor use!) in the #vehicle interior is the worst position: The #vehicle roof shields signals, #roof pillars ensure high signal noise, the vehicle interior also reflects signals. An exact measurement is almost impossible.

oblique, sideways:

Antennas that are mounted outside, but at an angle, also shield signals and receive reflections, e.g. from the asphalt or vehicle body. The antenna is horizontally polarized so it only accesses the few satellites on one side of the vehicle. Valid data is coincidence.

2 or more antennas close together:

GPS antennas interfere with each other. The signals for the systems are also noisy.

Minimum distance must be 200 mm radius to each other.

Missing conductor under the antenna as a shield:

Vehicles with a plastic body: Normal GPS antennas require a conductive base plate with a radius of approx. 100 mm. This prevents signals from being reflected from the space below the antenna and causing increased noise. CFRP is a very good conductor. GRP does not conduct.

Permissible and non-permissible mounting locations on the racing vehicle:

If you really want to work validly with #GPS data recording systems, you have to follow these installation instructions - 90% of all data quality problems, system failures or incorrect measurements are due to carelessly installed GPS antennas.

That's why we only use the best quality in our own racing vehicles: Racelogic measuring systems!

Warm greetings

Jürgen Albert

master mechanic

HERE you will find Racelogic GPS and camera systems in our shop