GDOP
One common problem with GPS
is known as geometric dilution
of precision (GDOP).
A GPS receiver may read the wrong position
(i.e. latitude, longitude,
and altitude) if the angles from the satellites
to the receivers are too small.
The GDOP is determined using geometric
relationships between the receiver
position and the position of the
satellites the receiver is
using for navigation.
Satellite Visibility
Another common problem with
GPS is that satellite signals
are commonly blocked by most
materials. GPS signals from
satellites in space (11,000
miles away) are not strong by the
time that they reach Earth.
Thus, GPS signals will not be sent
through buildings, metal, mountains,
or trees. Leaves and jungle
canopy can attenuate GPS signals
so that they become unusable. In
locations where at least four
satellite signals with good geometry (GDOP)
cannot be tracked with sufficient
accuracy, GPS is will not work.
Speed Limits
Some GPS receivers have built-in
speed limits, so that if a device is
moving above a certain speed,
it will not work properly. A receiver
that is meant to be used in
a car may not work in an airplane.
Less expensive GPS receivers,
such as handheld receivers, must
be held virtually still in
order to receive an accurate reading. Thus,
a large number of handheld
GPS receivers cannot be used while moving
(i.e. in a car, airplane, or
ship).
Temperature Limits
GPS receivers, like most electronic
devices, have temperature
limits. GPS receivers
cannot handle extreme temperature
conditions, such as the Arctic
or the Mojave Desert. The temperature
limits on GPS receivers vary
by the manufacturer. However,
most handheld receivers range
from 5 to 157 degrees Celsius.
For more information on problems
with GPS please refer to the
geography
department at the University of Texas.