Endurance.Net Ridecamp Archives

Hello Kathy,
I use a Garmin GPSmap76S. I live in San Diego. I am a surveyor by 
trade and use this unit at work and also measure endurance rides with 
it. I always have it set on "distance 0.01mi" which means it takes a 
reading every 53 feet +/-. I have 3 different types of software that 
I use to store the data and also make maps. This unit has extra good 
sensors and almost never loses signal. I plot the data on Nat'l 
Geographic "State Series" California Topo Software, also on Garmin 
"MapSource" software and sometimes on "OziExplorer" software which 
uses very recent USGS Aerial Topo that must be purchased specifically 
for each area you want to map but it has a lot of detail. When the 
unit does lose signal it shows up on the plot but the software topo 
is very detailed and often shows the trail I have been riding so I 
can fill in the missing sections to get the mileage as correct as 
possible. Every time I check the GPS mileage against the mileage from 
following the trail on the software topo using the mouse they agree 
within 2-4% (1-2 miles in 50). I have GPS'd over 10 rides and several 
of those on 2-3 different years. Where the trails are the same I get 
the same mileage so the unit is consistent. There has only been 1 
ride "Bar-H-Boogie" that measured 50 miles and I got 50 on both days. 
All the rest have been 43-46 miles with the shortest being "Hog Wild" 
the year it rained so hard they had to eliminate a loop and it 
measured 38 miles both days. On 2 desert rides I got 45-46 and an 
Etrex unit got 43-44. I have checked my unit with hwy mile markers, 
with my truck speedo (calibrated at a speedometer shop), with 2 
software mapping programs and with various survey control points so I 
know it is accurate.

Suggestion: I think there could be a line on the vet card for the 
type of GPS unit and a line under each vet check for mileage. Then 
RM's could get a good average mileage from a lot of different units 
for every loop on their ride and adjust things if they want.

Nice topic, are you going to post some kind of results or ...?

Don Huston



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