Chapter 2 Geode Features 7
Owner's Manual
For the Geode in ideal conditions, 95–98% of the points on
a scatter plot will fall within a sub-meter radius of the true
point.
GPS manufacturers quote their accuracies in different ways.
They use different statistical descriptions of probability. A
GPS receiver may be sub-meter. That is, it may be able to
plot points within a meter
radius of the true point.
However, those points may
only fall within that meter
radius, 50–60% of the time.
The accuracy for those
receivers is sub-meter, but
the precision is only 50–60%.
These claims largely depend
on the statistical method
used to calculate accuracy.
One manufacturer might use
circular error probable (CEP),
a calculation that qualifies the data as sub-meter only 50%
of the time. Another could use root mean square (RMS),
denoting the data is only truly sub-meter around 65% of the
time. The third manufacturer could use twice the distance
root mean square (2DRMS), a measure that indicates the
data as sub-meter accurate around 95–98% of the time.
2.2 GPS vs. GNSS
A GPS receiver’s reliability refers to the consistency with
which it is able to secure enough satellite signals to produce
accurate, precise positioning. This becomes a challenge
when the receiver’s immediate surroundings interfere
with its line-of-sight to the satellites. For example, tall trees
and buildings are common challenges to GPS receivers’
reliability.
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