The 48-hour precision survey in Lady Heather uses a statistical weighted median
filter to arrive at its final location instead of a simple average of fixes.
It processes data of one minute, hour, and overlapping 24 hour intervals to
calculate the final position. It can produce a location that is 3-10 times
better than simple averaging of the fixes.
A further complication is storing the precise location into the receiver. The
Tbolt firmware only lets one write the location using single precision floating
point numbers (24 bit mantissa). This is well below the desired resolution of
the position. Lady Heather gets around this by limitation by doing a royal
kludge. Once the precise position has been calculated, it issues single point
survey commands to the receiver until one just happens to lie within one foot
of the calculated position.
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