GPS Tracklogs

GPS devices log position and elevation at frequent intervals and record the data in tracklogs. These can be uploaded to websites or PC-based software to calculate climbing. Some GPS devices produce a climbing figure directly.

The climbing figures produced by different devices can differ quite markedly from each other and can be significantly higher or lower than a contour count-based figure for the same route.

GPS tracklogs can provide evidence of the climbing in calendar events and permanent events, but for the above reason should be forwarded to the AAA Man for assessment for AAA. DIY by GPS tracklogs with AAA potential are normally forwarded to the AAA Man for assessment automatically, but a reqest to do so when the tracklog is submitted to the DIY Organiser for validation will make sure this happens.

Over the last couple of years various websites have been reviewed regarding their usefulness for AAA, and progress so far will be reported here in the coming months.

GPS devices with barometric altimeters

Some devices use just the GPS signal itself to work out elevation. Fluctuations in the signal occur cyclically and cause the derived elevation to fluctuate over time. Anomalies can also be caused by the terrain, e.g. in narrow valleys, amongst tall buildings, under trees. More recent models with a more sensitive GPS receiver are less prone to these problems. Some devices have built-in barometric altimeters to smooth the GPS-derived elevation, and are preferred for AAA. But these can be affected by changes in the weather.

GPS Calibration

Older devices can take up to half an hour to calculate a reasonably accurate elevation figure. I've seen tracklogs starting at Marple with altitudes varying between 150m below sea level and 300m above sea level! The solution is to calibrate the elevation to the height of the start point before setting off. Newer devices, e.g. Garmin Vista HCx, 800 and 1000 series, correct the altitude automatically much more quickly, so there is no real need for manual calibration.

GPS Trackpoint Interval

A GPS tracklog is made up of trackpoints recording position and elevation, which are inserted into the tracklog as the ride progresses. The AAA needs trackpoints to be recorded every 100m, preferably more often. Older devices needed to be set manually to this frequency. More recent devices record far more trackpoints automatically, typically 2,500 trackpoints or more per 100km, and don't need setting.