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RE: [RC] GPS data - Bob MorrisKathy: When I was doing trail mapping a few years back I used a Trimble survey grade unit with differential post processing. Repeatability of a known route was in the range of one to two meters. Point location one meter and route accuracy as determined by plotting the route in ArcView and over laying State of Idaho corrected orthophotos was usually with in one or two meters. Overlaying the USGS Quads showed that the quads depiction of the trails system was very, very inaccurate. I used a logging period of five seconds. That is a known location and elevation every five seconds. On a horse, which I used quite a bit , that means a position every few feet. On a motorcycle, used on occasion, that means that at 30 mph (seldom obtained off road) a position every 44 feet. Fairly close even on irregular trails. Yes, on occasion the signal was lost. That makes you either stop and wait or you go back and re do a short section to get the exact measure. The ArcView soft ware utilizes all the Trimble output including elevation to produce a very accurate trail length. I estimate that we mapped between 750 and 1000 miles of trails here in SW Idaho for horse and motorcycle use. One must realize that not every endurance rider has access to survey grade GOS and software. However, if you are working with a governmental agency like the BLM or the USFS they do have the equipment and often are happy to get the trails mapped. But you have to ask, and ask and ask. Bob Bob Morris Morris Endurance Enterprises Boise, ID -----Original Message----- From: ridecamp-owner@xxxxxxxxxxxxxxxxx [mailto:ridecamp-owner@xxxxxxxxxxxxxxxxx] On Behalf Of magnumsmom@xxxxxxx Sent: Tuesday, March 14, 2006 9:18 AM To: donhuston@xxxxxxx; ridecamp@xxxxxxxxxxxxx Subject: Re: [RC] GPS data Hi Don, Thanks for the input. Yes, the idea is to put together an article if we get enough feedback / information. Thanks, Kathy Myers in Santa Fe, NM -----Original Message----- From: Don Huston <donhuston@xxxxxxx> To: magnumsmom@xxxxxxx; ridecamp@xxxxxxxxxxxxx Sent: Mon, 13 Mar 2006 23:17:20 -0800 Subject: Re: [RC] GPS data 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 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- =-=-=-=-= Ridecamp is a service of Endurance Net, http://www.endurance.net. Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp Ride Long and Ride Safe!! =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- =-=-=-=-= =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Ridecamp is a service of Endurance Net, http://www.endurance.net. Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp Ride Long and Ride Safe!! =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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