GPS in Automotive Testing: how did we get here?

The road to acceptance of GPS as the principle method of vehicle test and validation was not an easy one

It will probably never be known whether the US government fully understood the ramifications of flicking the switch on GPS selective availability in May 2000. The descrambling of the publicly available (but not particularly useful) signal meant that the positional accuracy of GPS receivers became ten times better overnight. The number of GPS users at the turn of the century was approximately four million: now there probably isn’t anyone living in the developed world that doesn’t use it. Exponential growth, to put it mildly.

Such a dramatic change in technological infrastructure happens extremely rarely, especially one which costs nothing.

At the time, vehicle dynamics testing generally relied on fifth wheels, radar, microwaves, and optical sensors – which all had various disadvantages. A fifth wheel was often difficult to fit to a vehicle body and was easily damaged; microwave was very sensitive to ride height and suffered measurement noise; radar was accurate but only when measuring speed from a static position aimed at a specific point; optical sensors really didn’t work in the rain. It might have been headline news at the time, but the change to the GPS signal forced through by the Clinton administration went largely unnoticed within the automotive testing fraternity, where scepticism surrounding the advantages of GPS remained firmly in place.


When we first came out with VBOX products, it was to a sector which wanted better testing methods and equipment, but which took some considerable persuasion that GPS was the way forward. Some of this was probably caused by the press release issued on the day that selective availability was removed:

“Even with SA turned off, GPS alone will not meet all users needs. For users with higher accuracy, availability, and integrity requirements – such as commercial airlines, ships navigating within harbors, railroads performing precise train control, precision farmers and miners, and surveyors – GPS will still need to be augmented locally with high-fidelity error correction systems based on differential GPS (DGPS) technology.”

Whilst this was and remains true in certain circumstances, the fact that speed, acceleration, and distance can be measured to quite remarkable levels of accuracy without DGPS correction was initially met with blank non acceptance.


A New Era in Automotive Testing

The first VBOX recorded GPS samples at 20Hz – a feature which itself raised a few eyebrows even amongst the forward thinkers, who assumed it was interpolated from 1Hz. The truth was that it contained one of the very first survey-grade GPS engines, capturing Doppler-derived velocity at a true twenty times a second. By 2004 we were selling a growing range of loggers and had launched the 100Hz VBOXIII, a big step forward in precision testing. A reliable DGPS base station solution fixed the positional accuracy, too. By this point, most test departments were finding that their fifth wheels and radar sensors were no longer required, and vehicle development using GPS was firmly established. A large step in automotive technological advancement had begun.


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