Of course need network lah, if not, how to locate your position,
GPS is never mend to use as a on time guide, it should
be use only as a pre journey planning map to calculate est the
distance, the exit, the time and the best route.
Layman GPS like google map, waze, one map, street
directories or even those GPS gadgets are best only at
stationary position, not moving position, like you walk, you stop,
you view, then you decide, but for car, it is moving fast, way too
fast for layman GPS, by the time you passed, the
GPS then follow up, the lagging is about 10 seconds or
worst.
Commercial and military GPS uses different
satellites, solely mend for them, not for general use like our
layman GPS that just use land parabola or bukit timah
tower signal, or sentosa ground satellite.
Like airport planes and military equipment or govt security
equipment and vehicle, they uses different bandwidth and satellite,
can hv pin point accuracy at any given time.
The pre warning can be once or twice before a turn. So at times
can be misleading. Though it has its flaw, it really help alot.