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Jim:
Glad to see people getting interested in using the GPS for trail work.
Sorry but I must throw a slight glitch or two in here BUT:
Until the Government, the Department of Defense, ends its selective
availability, there is always the introduced error factor. It can be in
excess of 100 meters. In fact the published accuracy at 95% of any given
time is "within 100 meters". Still better than anything else.
If you can down load the gathered data and do a differential correction,
them you can get to submeter accuracy. With out differential correction I
have found the total mileage can be off up to 20%. I no longer rely on raw
data for ride mileage. I refuse to even guess until I have reduced the data.
I would be very interested in the software used with the Garmin. The Trimble
software is $2,500 if you buy it separate from the GPS unit.
Also, do you know what form the Garmin downloads the data in? Is it RINEX or
SSF??
Using 2d data can be very risky if you have any appreciable elevation
differences (I am quite sure you do down there) Check back on your spherical
trigonometry. I have not had very much trouble in canopy cover. If it is
very dense like with deciduous trees then it might but fairly open conifers
have not bothered me much. Of more concern has been the availability of
satellites. I will not survey with out four and a PDOP of less than six.
Otherwise I have to sit and wait.
Incidentally the last launch that blew up contained a new satellite. We will
have to wait a while for any new ones I guess.
Bob Morris
Morris Endurance enterprises
Boise, ID
Keep up the good work but be careful about stating mileage to ride managers
until you can use corrected data.
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