A New Technique Makes GPS Accurate To An Inch (gizmodo.com)
A team from the University of California, Riverside, has developed a technique that augments regular GPS data with on-board inertial measurements from a sensor. Actually, that's been tried before, but in the past it's required large computers to combine the two data streams, rendering it ineffective for use in cars or mobile devices. Instead what the University of California team has done is create a set of new algorithms which, it claims, reduce the complexity of the calculation by several orders of magnitude. In turn, that allows GPS systems in a mobile device to calculate position with an accuracy of just an inch.
This is incorrect. President Clinton removed selective availability from GPS. That is why we have the location boom today. We are at as accurate a position as we can be with the GPS reception. This happened in 2000. There are other forms of signal degradation that are available. SA is not an issue anymore. I am a professional land surveyor. Multi-pathing is currently your greatest hurdle to overcoming highly accurate positioning. That unfortunately, requires fairly complex calculations to remove it properly. Even with my highly accurate receivers, I have to remove multi-pathing manually sometimes. Reflection is a harsh mistress.