Re:Japan's Plan for Centimeter-Resolution GPS
by ghshephard on Saturday April 26, 2014 @08:59PM
(#7653409)
Back in 1995 I wrote the mapping software for a "Tundra Tracker", this was the navigation software for a supply vehicle that could navigate in the arctic in whiteout conditions. The idea was to have someone drive a path while conditions were good, and we would then lock in all the waypoints. Rather than store all the waypoints for the path, we were able to eliminate about 99% of them with various splining algorithms.
One of our big concerns back then, though, was that US Military would degrade the SA (Selective Availability) signal - it had happened in the Gulf War, and our tracks, which were normally accurate to within 3-4 meters, went wacky and were almost 50 meters off at times.
The solution was to mount a radio antenna, have it calculate it's "True" location by averaging a couple days worth of GPS signals, and then, continually transmit the difference between a current GPS signal and it's known location. This Differential GPS let us calculate paths to within 1m of accuracy.
When I asked what prevented a military opponent from doing the same thing, I was told that the first thing in the battlefield that gets hit as a command center would be anything transmitting RF, particularly if it was believed to be for D-GPS. Also, D-GPS isn't that effective for missile tracking, as you need to get differential signals in areas outside of your zone of control.
One of our big concerns back then, though, was that US Military would degrade the SA (Selective Availability) signal - it had happened in the Gulf War, and our tracks, which were normally accurate to within 3-4 meters, went wacky and were almost 50 meters off at times.
The solution was to mount a radio antenna, have it calculate it's "True" location by averaging a couple days worth of GPS signals, and then, continually transmit the difference between a current GPS signal and it's known location. This Differential GPS let us calculate paths to within 1m of accuracy.
When I asked what prevented a military opponent from doing the same thing, I was told that the first thing in the battlefield that gets hit as a command center would be anything transmitting RF, particularly if it was believed to be for D-GPS. Also, D-GPS isn't that effective for missile tracking, as you need to get differential signals in areas outside of your zone of control.