By STATIONMAN
10 September 2008 08:51
Does anybody know why the distance on a saved track is always less than the total odometer distance for the walk on a Garmin Vista HCx?
Answer
By Country Walking magazine
We contacted the Garmin helpdesk on 0808 238 0000 for advice:
“The GPS keeps two separate records of the distance you are travelling. Firstly, there’s the Trip Odometer which is just like the trip odometer on a car. You reset it before you start and it will keep track of the distance travelled until you reset it again.
“Secondly, the GPS is recording a Track which is a breadcrumb trail of where you have walked. This is normally displayed on the map screen of the GPS, and you would reset at the start of your walk and stop at the end. The Track is recorded as a series of points joined by lines, and the GPS records a point every time you change direction, speed or altitude. The track is recorded as the active track, which you can save into the memory, reset the track back to zero and do another walk to create another track.
“However, when you save the track four out of five track points are stripped out, leaving a lot fewer points joined by straight lines - so the distance travelled is reduced. The maximum size of a saved track is 500 points so if stripping out four in every five doesn't bring the track to below 500 points, the GPS will strip out as many as is necessary to reduce the track to 500 points. So a very long walk will have a lot more track points stripped out, therefore simplifying the route and removing bends, corners and zig-zags, and resulting in a shortened distance measurement.
“If you don't want your track shortened, stop track recording when you get to the end of the walk and don’t save the track – then download the full active track to your PC.
“There is also another situation that can arise, when the Trip Odometer and Active Track show different distances travelled. This is due to a loss of GPS signal – the Trip Odometer will not record any time/distance data where there is no signal, but the Track will compensate for the missing data by putting a straight line between the points where the signal was lost and acquired again, resulting in a discrepancy in distance.”