Alpine NVD-T003 Owner's Manual page 7

Locations where GPS signals are received easily
Locations where GPS signals cannot be received
In the following locations or conditions GPS signals cannot be received. However even in these locations, the gyroscope
and speed sensor will provide a substitute means of determining the vehicle's position and the system will be able to
continue to track the vehicle's progress along the route.
In tunnels and indoor parking lots
On the bottom level of double-
decker motorways
The optimum locations for receiving GPS signals
are locations that command a good view where
there are no tall buildings, trees, or other objects to
obstruct the signals.
Locations surrounded by tall
buildings
When a GPS satellite is low on the horizon (angle below 10°),
obstructions sometimes make normal reception impossible
Locations surrounded by tall
trees
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