Tag Archives: www.ridewithgps.com

Wide Variance in Altitude Gains using same gpx Data File

I’ve been using my Garmin Edge 305 for a while, and I’ve always wondered how accurate the elevation gain is on the various applications used to track gps data.  Using the same data, shouldn’t the elevation gain be the same, no matter which program you use?

I have 4 different applications to interpret gpx data … connect.garmin.com, Ascent, SportTracks, and ridewithgps.com.  I took about a 2.5 week sample (some with deep canyons, others were just hill climbs), and I saw a huge variants.  From this sample, connect.garmin.com seems to run low, http://www.ridewithgps.com seems to run high, while Ascent is the one that comes closest to the average.

Description connect.garmin.com Ascent GTC SportTracks ridewithgps Average
Crown/Starlight Crest 2465 2284 2420 1623 2416 2241.6
Mt. Hamilton 4892 4952 4973 4777 5052 4929.2
Page Mill, OLH, Kings 5743 6013 6148 5088 6270 5852.4
Morgan Territory, Mt. Diablo 5855 6167 6286 5189 6344 5968.2
Montebello, Mt. Eden 2670 2820 2932 2432 2943 2759.4

Taking a look at Morgan Territory/Mt. Diablo.  This had climbs mostly out in the open, without too many shades.  However, notice the big difference between http://connect.garmin.com and http://www.ridewithgps.com

The average is 5968 feet, with Sport Tracks at a low of 5189, and ridewithgps at a high of 6344.  Ascent seems to be the closest, being a little higher than the median, followed by connect.garmin.com (although it is a little on the low side).

Based on this, I think the most accurate reading will be from Ascent.  Talking to Marco, it seems that some software applications use digital elevation model underlay, and depending on which version each application uses, the resulting elevation gain may vary, even though the same source data (from the gpx file) is used.

Even though http://www.ridewithgps.com reads overly high, I still like to use it, because when you hover over the elevation profile, you can actually see the percent grade of the hill you were climbing, speed, and distance.  Ascent is more accurate, and I like the way the graph are more vectored, and yes, more geekly looking than connect.garmin.com is.  If there is one thing I wished Montebello Software could do with Ascent, is to give you a summary, in table form, giving you at a glance, stats like elevation gain, speed, distance, etc.  Right now, you have to click the calendar, and drill down to the data you want.

Now what am I getting at?  Well, from an Engineering standpoint, it doesn’t make sense.  If you have the same data file (gpx file), and same data points, why shouldn’t you get the same elevation gain?  Or maybe the gpx file does not give you the actual elevation data … who knows, and that elevation data is based on something else?  Who knows????