The Global Positioning System, used by pedestrians, motorists and truckers the world over is a free application developed and maintained by the US government. The Air Force “develops, maintains, and operates the space and control segments.” As the system of 24 satelites orbits the globe, they transmit signals containing the time and current position. GPS internal standards seek to provide three dimensional location accuracy within a range of 7.8 meters 95% of the time. In practice, users often have positions accurate to within a meter of their actual location.
The accuracy of GPS can be improved by using systems to augment the basic signal provided by the GPS satellites. The Japan Aerospace Exploration Agency (JAXA) has a is developing a project for $1.2 billion called the Quazi-Zenith Satellite System, which will involve 7 satellites orbiting in an asymmetrical figure-8 pattern that narrows over japan and swings down as far as Australia in the Southern Hemisphere. In addition, the system includes 1200 reference stations whose position has been surveyed to great accuracy. Together the satellites and reference stations will be able to correct inaccuracies in the GPS system caused by Japan’s Mountainous terrain and atmospheric interference. The augmented system will provide locations on the centimeter scale which will lead to improved services and new applications of the technology.
The system is constantly improving with a multi-billion dollar budged funded by the Department of Transportation and the Department of Defense. GPS was formerly operated with a Selective Availability (SA) feature engaged which degraded the civilian GPS signal significantly. President Clinton oversaw the Department of Defense turning off this feature at the end of his second term which led to a tenfold increase in civilian accuracy with the GPS system.
As the accuracy of GPS continues to improve, other applications of the technology can develop including autonomous farming, planes that fly on their own and perhaps even vehicles that can drive themselves accurately within current lane widths.
Unless I’m mistaken, the accuracy of standard GPS is still partially limited by the Department of Defense, though surveyors and others with special needs can get enhanced systems. So why is JAXA doing their own thing? One aspect is their space industry lobby, which is 100% dependent on government funds. The other is that (as noted) GPS is ultimately controlled by the Joint Chiefs of Staff and POTUS and can be turned off or degraded. While it’s never been used for political purposes, satellite and rocket makers around the world use that to lobby for “independent” systems.
Now how accurate do vehicles need GPS to be? – I don’t know. How much does GPS degrade in a thunderstorm? Your bar graph tells that story: GPS is good to within 2 feet most of the time, but the tail matters! Are roadside sensors the way to go, rather than highly detailed digital road maps?
As far as roadside sensors go, the article about the google cars which uses sensors, stated that the rain still caused a major problem with those as well. A GPS system might not work in a thunderstorm, but so far neither does the technology we have for sensors. Weather is a major concern in terms of the automated vehicle’s future.
It’s hard to see the benefit of such degradation that only worsens your position by 2 meters. Militarily, enemies don’t need to hit a target that small if they have bombs and civilians aren’t radically affected by such a small inaccuracy. Since the satélite is only broadcasting location and time, processing speed shouldn’t be a bottleneck either. They’re probably pretty close to their potential up there without adding more infrastructure.
But if you’re driving a car, being off by 2 meters would frequently be fatal.
It is noteworthy to state that China is also developing its own system Beidou that is similar to GPS. Beidou offers equivalent or even better accuracy in its operating regions. For example, Beidou has been frequently used to track drug dealers in the South part of China. By 2016, Chinese “GPS” will be able to cover the entire Asia-pacific area. GPS may face intense competition from Chinese “GPS” by that time then.