Ride statistics query
Road Red
Posts: 232
A query on advertised climbing on sportives.
Looking at the King of the Downs route it is advertisied as 9,000ft of climbing, yet the profile on mapmyride seems to indicate about 5,000+.
It was the same on the Hell of the Ashdown.
Why is this and which is the correct figure?
Looking at the King of the Downs route it is advertisied as 9,000ft of climbing, yet the profile on mapmyride seems to indicate about 5,000+.
It was the same on the Hell of the Ashdown.
Why is this and which is the correct figure?
0
Comments
-
I dont know? Is mapmyride counting the downs as well as the ups??.
"Let not the sands of time get in your lunch"
National Lampoon0 -
Surely if it was counting ups as well as downs the figure would be either double or zero? presuming the same start and finish point. :?
Why there should be difference the OP stated I have answer.
Last year I did the Buttertubs ride from Catterick and the posted gradient indicated it was 9-12%, however my Garmin later indicated 18% - I bonked. I still cannot rationalise the difference, perhaps it's the sat-nav conundrum.0 -
I really don't rate the accuracy of the mapmyride elevation counter. I did a local loop that include two reasonably sizeable climbs totalling 250 metres in isolation. Coupled with a numebr of smaller undulations, I got the route to around 400-450 metres climbing by looking at an OS map. Maymyride calculated around 270 metres of climb. If you look at the elevation profiles, they just don't closely reflect the terrain you dragged your sorry ass over.
Bikely, (sorry no link) came up with 420 metres for the same route and when looking at the profile I could visualise the roads I had just ridden over.0 -
All of these are to do with digital elevation models (DEMs) and their relative accuracy. A DEM is just a grid of points, each of which has a height associated with it. You can have a coarse DEM with maybe 1000m between each point on the grid or a detailed DEM with only 50m or less between each point.
mapmyride and other online mapping sites generally use a Google-derived DEM which is fairly coarse i.e. there is a big distance between sample points. So it tends to underestimate elevation change, because the big distance between sample points tends to smooth out the landscape. Figures quoted by sportive organisers often use data from the Ordnance Survey which is much more detailed, so tends to get higher values.
Of course, neither of them are right. Because the use of a grid means that you have to interpolate (an educated(??) guess) the actual height if you happen to be somewhere between the sample points. Sometimes that means that elevation figures can be exaggerated because the road actually hugs a hillside more closely than a simple interpolation between the points would suggest. And sometimes it reduces it because (e.g. mapmyride) the broad spread of points means that it misses out the true elevation, using lower values to either side...
All of this will of course impact on the gradient calculations too.
Of course, GPS measurements are a whole new can of worms...0 -
Map my ride is usually less than my GPS and also map calculations. It's usually way off as well - not even close!0
