I'm curious about the $100,000 GPS system. They sell GPS add-ons for $70. So what kind of GPS costs $100,000? Military, I suppose.
1. A part of the error on GPS is due to things like radio signals slowing down as they travel through the ionosphere. If you set up a GPS base station at a known location, you can take GPS measurements, work out the errors due to the ionosphere (and similar things), transmit that to the receiver on the car, and subtract the errors there. Within a few kilometres of the base station lots of the errors will be common - so a lot of errors are eliminated. (if you don't want to operate your own base station, there are services like Omnistar which operate a network of them and radio out the corrections, for a few thousand dollars a year subscription). High cost receivers support doing this!
2. The GPS signal is comprised of a digital signal with a wavelength of about 300m (which we can measure accurate to about 3m) and a carrier wave with a wavelength of about 19cm (which we can measure accurate to a few mm) - but the carrier signal is a sine wave, so it has an 'integer ambiguity'; 1,000,000.1 wavelengths looks identical to 1,000,001.1 wavelengths. High cost receivers can perform 'integer ambiguity resolution' to figure out the integer number of wavelengths, allowing high precision positioning.
3. There's an encrypted military GPS signal at a different frequency - but using certain tricks you can receive the encrypted military signal. By combining two sine waves using a trigonometric identity, you can get a 80cm sine wave - which means there are fewer ambiguity options, making ambiguity resolution faster. Consumer receivers don't attempt this because you need to receive two GPS frequencies instead of one, and at both frequencies your receivers need ten times the bandwidth.
4. Once you've got high precision GPS, you can put one receiver at the front of your vehicle and one at the rear, giving you a 'GPS compass' which can tell you which way your vehicle is pointing, even if you aren't moving. Of course, using two receivers means paying for two.
5. GPS measurements can be combined with measurements from an intertial measurement unit (IMU) - a sensor system with gyroscopes and accelerometers which can give fast updates, but which are prone to drift over time (as they're based on integrating acceleration to give speed and accelerating speed to give position, a small acceleration error eventually leads to a big position error). The more you spend on your IMU, the lower the drift rate. GPS measurements aren't prone to this drift, but there can be GPS outages (e.g. when going though tunnels) and GPS receivers don't give measurements as fast as an IMU can, so you combine GPS measurements with IMU measurements, usually using an extended Kalman filter.
6. Radio waves can reflect from trees, buildings, and the ground. This is called 'multipath'. High cost receivers use expensive antennas (like choke ring antennas) which have lower gain at lower elevations - which reduces problems with signals reflected from the ground. These antennas are more expensive to manufacture than consumer receivers.
7. Mobile phone GPS chips are produced by the million. The market for high-precision GPS is very much smaller, so the costs of engineering all the above have to be recouped over fewer units - so the equipment is expensive.
In summary, when you spend $100,000 on a GPS system you get a base station and radio link, two rover receivers, all the receivers are capable of receiving the military signal, you get special software that can perform ambiguity resolution for centimetre-precise positioning, you get three high quality antennas, and you get a high-precision IMU and software to go with it.
A lot of this technology could probably be made a lot cheaper if it were mass-produced and installed on every car, as a lot of it's in electronics and software. But in the world of robotics there are a great many sensors that cost $100,000 but could be made a lot cheaper if someone wanted to order a million of them.
If you're interested in autonomous vehicle technology, I advise you to check out The Great Robot Race - it's a good documentary.
Even if they could make the GPS more cheaply, wouldn't this imply that they expect the very accurate military-grade GPS service to be available to consumers in future? Galileo was abandoned, wasn't it?
Right now, if you're a farmer, you can buy a GPS autopilot system with high-precision GPS receivers which will link into your tractor's power-assisted steering and guide your tractor down crop rows with centimetre-level precision. Off the shelf, for maybe $40,000.
Galileo's still going - used together with GPS, high precision GPS will become simpler and more reliable.