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Mapping offset error - Printable Version

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Mapping offset error - dmather - 18 Jun 2019

Hi Colin,

Having a bit of a nightmare.  

I created a 100 mile route - first by creating 8 legs, then using a text editor to knit them together.  All went well (except it got shortened to 99.77m when knitted together).  But when I hit 'refresh elevation' (without actually having done any editing), something very odd happens in relation to elevation and it is that is the apparent bug I want to discuss.

On the 99.77m route, if I was to focus on the top of a specific hill...  then it might measure, say, 1100 feet...  and if I look at the 'Terrain' map, the contours would tie in well with the elevation readings.  But as soon as I press the refresh elevation button (or indeed if I edit the route), then it's as though all the elevation shifts off to the side somewhere.

The marked route will still visually pass over the peak of that hill.  The contours will still read the equivalent of 1100 feet.  But the elevation reading might say 350 feet.

If I move along the route, "down the hill", then the elevation can be going up (or down).

It's not random. the general shape of the new elevation profile clearly has some relation to the original elevation profile.   It makes me think that the elevation data is being taken from a line perhaps parallel to the real visible line... but offset by maybe quarter of a mile or something - and a quarter of a mile away the elevation profile can be quite different.   Except there is one point at about 42 miles where the elevation profile becomes negative which I cannot begin to explain, so my theory might be wrong.

All I want to do is edit the route to extend it to 100m for an upcoming race but if I do that, I get this weird elevation effect that will ruin the credibility of the data I'm sharing. 

I think I've seen the same phenomenon on the RunWalkCrawl route for the SW50 ultra I'm doing on Saturday  (not sure if I'm getting mixed up, to be honest.).

Do you have any idea what this is?

More bullet point information

Sample route  https://gb.mapometer.com/running/route_4925474.html

I tried saving as tracks  and routes.  Both give the same output.

I tried uploading the gpx into mapmyrun and strava (I'm not really familiar with those)  but the route was shortened even more (presumably they compress the data more)  and generally not helpful.

I'm using Chrome on a laptop.  I tried Edge and got the same.

Any ideas?  Thanks?