Originally Posted by dan828
I have a Garmin eTrex Vista (standard handheld GPS unit) that I use while riding (reads out mileage, avg moving speed, etc.). It does occasionally lose signal with overhanging trees, but it snaps to your location when it reacquires the satellites, and just ignores the missed time for the moving avg and what not, and it appears to just draw a straight line between signal loss and reacquisition so far as the mileage goes.
Pretty much right on. I use an eTrex in the car and on the bike, and download the tracks to the computer when I get home. What you can see at higher car speeds is that the GPS doesn't continuously monitor position, but takes samples of position at defined intervals, and calculates distance & speed between the samples. The faster you go, the farther distance apart those intervals become. Track a long sweeping curve at high speed with a GPS and it shows up as a series of short straight lines connected by sample points. So slight dropouts from branches, etc. aren't usually any problem, especially at the lower speeds of a bicycle. The sat. signals are pretty robust, and can usually filter through all but the densest foliage. Tall buildings can be a problem, but as long as you're moving, the GPS should reacquire signals as you move past obstructions.