Re: RC: RE: Marking an Endurance Ride with a GPS

[Truman Prevatt <tprevatt@mindspring.com>]

No Bob you are not old fashion - just old, but you are correct. The GPS
technology is absolutely fantastic and our military superiority is
enhanced by it. It can guide a bomb through a window. However, it cannot
be guaranteed to help mark an endurance trail!

I've been associated with the NAVSTAR GPS program off and and on since
the mid 70's. I've been working precision geopositioning programs for the
past 25 years - GPS being only one such program.

Any technology needs to be understood as for as it's limitations before
it is embraced as gospel. GPS does have limitations. It was designed for
one particular mission - marking endurance trails was not it.  My spouse
keeps telling me I should write an article for EN on GPS - what it is and
what it isn't. Of course I don't listen to her, maybe I should start.

Bottom line is for normal terrain on the earth, with forest, with
canyons, etc. we cannot depend on GPS estimations of distance to be
accurate. In fact there is no specification on the GPS program for
accuracy of measured distance. The specification or on location and time
transfer with three spacecraft visible for 5 minutes and a separate
specification for location accuracy and time transfer accuracy with four
spacecraft visible for 5 minutes.

These conditions may or may not have anything to do with the world of
endurance trails.

Truman





Bob Morris wrote:

>
>
> Perhaps I am being old fashioned but I have GPS'd many
> hundreds of miles of trail with survey grade instruments and
> am very aware of the problems. Had to sit waiting one day
> for over an hour to get readable satellites. Would you want
> to do that during a ride?
>
> Bob Morris
>