GPS computers

[Spookytooth]

I have recently purchased a Garmin Edge 200 which is a little great gadget for tracking all your cycling data if you are into improving circuit times etc. Previously I have logged my courses on Mapometer which is a PC based bit of software only but uses OS mapping data I believe.

One thing I have noticed when comparing the same route on Garmin Connect and on Mapometer is the relatively large variation in the altitude ascent calculation. Does anyone have any thoughts on which may be the most accurate?

Thanks

 

[StuAff]

Are you enabling elevation correction on GC? The raw altimeter data on my Edge 705 is generally about 30% higher than the corrected version.

 

[Spookytooth]

Are you enabling elevation correction on GC? The raw altimeter data on my Edge 705 is generally about 30% higher than the corrected version.

I didn't know about elevation correction. I assumed the downloaded data from the device did it all for you. I'll take a look at my software settings and see if I can adjust these. Your Edge 705 sounds like a more sophisticated device but hopefully the Edge 200 has the same facility.

Many thanks

 

[StuAff]

The correction is down to Garmin Connect, not the device, you enable it (or not) for each ride you've uploaded (there's an 'on/off' button on the details page for each ride). The 705 has a barometric altimeter, supposedly more accurate, though not in actual use IMHO, the 200 is just using GPS data which will be less accurate. Once you've got correction enabled, the stats should be largely identical wherever you're looking at the data.

 

[Spookytooth]

Yes, I have now located the button to enable elevation corrections but I notice this is the default setting so this has been factored in already. My last ride was over about 15 miles - GC gave and ascent of 1003ft whilst Mapometer gave 1296ft. Quite a difference. So, I am still unsure as to what is going on and which is likely to be the more accurate figure. I realise there will always be a bit leaway either side but we are looking at 30% here. If I was a bit OCD (which I may be) I could do some calibration between known altitudes as defined on the OS map. When I get time I let you know my findings.

 

[Spookytooth]

Following on from my earlier post some while ago I have done a bit of research into these altitude variations between the two software formats. I have concluded that the Garmin Connect has to be more accurate than Mapometer. The various reference points for altitude appear to be much the same for both Garmin and Mapometer but riding between the two points gives varying data. I have noticed that on a purely uphill ascent with absolutely no level/downhill element the Mapometer still shows some descent reading. The Garmin Connect gives only an ascent reading in this situation which is what I would expect. So, my initial thoughts are that I will trust the Garmin data before Mapometer.

 

[Crackle]

None of them are reliable. They all use the same map tiles which can be quite coarse in their elevation mapping, then each of them use an algorithm to correct for this error. Mapmyride used to be the most accurate but I stopped using it when it became very slow, it might be better now. Sporttracks is another pice of software you could use with your Garmin, you can download elevation correction plugins and alter the elevation smothing. It also has many other features which you will probably find more useful than Connect, though many people use them together. Strava is another popular piece of software and there's a CC club but mainly because of the segments not because it's any more accurate.

 

[zoxed]

MyTourBook and Qlandkarte both support altitude correction with SRTM data:
http://mytourbook.sourceforge.net/mytourbook/index.php/documentation/tools/adjust-altitude
http://sourceforge.net/apps/mediawi...se_SRTM_data_as_Digital_Elevation_Model_(DEM)
http://wiki.openstreetmap.org/wiki/SRTM