Garmin ascent data accuracy
03-20-24, 11:02 AM
#26
Senior Member
GPS has insufficient accuracy for measuring cumulative altitude gain.
Civilian GPS is only accurate to 5m under idea conditions. The receiver has no way of distinguishing between a true vs false elevation change. The computer records a GPS data point each second, and there could be up to 10m of phantom elevation change between two data points. Under poor conditions it could be much worse than this. The cumulative drift would add up to thousands of phantom meters climbed over a ride.
Horizontal drift is not an issue because the inaccuracy averages out.
On GPS devices without a barometric altimeter, Garmin uses map data for elevation graphing. It never uses GPS data for elevation.
Garmin has an auto calibration feature that uses GPS data to self-correct any barometric altimeter drift due to weather change. Their documentation doesn't explain how this works, but presumably they're doing averaging to the GPS data. They also have a similar feature to auto-set wheel diameter and in my experience it is spot on.
Elevation climbed is a fun statistic to look at. I don't need it to be exactly accurate to the meter.
Civilian GPS is only accurate to 5m under idea conditions. The receiver has no way of distinguishing between a true vs false elevation change. The computer records a GPS data point each second, and there could be up to 10m of phantom elevation change between two data points. Under poor conditions it could be much worse than this. The cumulative drift would add up to thousands of phantom meters climbed over a ride.
Horizontal drift is not an issue because the inaccuracy averages out.
On GPS devices without a barometric altimeter, Garmin uses map data for elevation graphing. It never uses GPS data for elevation.
Garmin has an auto calibration feature that uses GPS data to self-correct any barometric altimeter drift due to weather change. Their documentation doesn't explain how this works, but presumably they're doing averaging to the GPS data. They also have a similar feature to auto-set wheel diameter and in my experience it is spot on.
Elevation climbed is a fun statistic to look at. I don't need it to be exactly accurate to the meter.
Last edited by Yan; 03-20-24 at 11:10 AM.
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