Long term averaging of GPS receiver readings, by keeping a
GPS receiver at a fixed location for many minutes, is a common
practice to improve the accuracy of fixed point location measurements.
Although trail accuracy is important in field guide maps,
it is impractical to do long term averaging for many minutes
successively at each of numerous sample points along a trail.
Fortunately it is possible to get the benefits of long term averaging
by averaging many logs of GPS receiver readings along a trail, even though
those trail logs can be recorded at various sample rates from a wide range of
GPS devices and in a wide variety of GPS signal conditions. Special logs,
called trail frames, help handle these variations by defining
where trails
- start and stop,
- intersect, and
- reach curve maxima.
An application called TrailFrame, which logs trail frame information into one
file and GPS NMEA sentences into another file, is now available for Palm OS
devices. The GPS log and trail frame file names
are simply timestamps of the start of data acquisition (an 'f' to denote 'frame'
is appended to the timestamp of the trail frame file name). And both
files are .csv (comma separated values) text files that are easily imported
into spreadsheet applications.
Currently under development is an online gadget that will read GPS log
files and trail frame files stored in online spreadsheets and produce a
long term averaged map of a trail.
