Re: GPS

B Lin wrote:

> Differential GPS depends on known land sites to send out GPS signals -
 > effectively becoming another GPS satellite, however they are limited
> by radio range to be effective.  Such locations would be known or
easily
> discovered and could be knocked out in a war, since they have to
> transmit to be effective.

Actually, before SA was turned off, there were a few sites that made 
differential GPS information available through the Internet. Not very 
useful unless you had a satellite or two in common with one of those 
sites, but...