[OSM-talk] [tagging] Feature Proposal - RFC - incline up down

Morten Kjeldgaard mok at bioxray.au.dk
Sat Aug 22 17:36:19 BST 2009


On 22/08/2009, at 13.14, John Smith wrote:

>> When subtracting two positions from each other, the
>> absolute positioning error will disappear.
>>
>> In addition, for many traces there will be multiple
>> measurements, which will give a much better determination of
>> the gradient.
>
> I disagree and I urge you to test this speculation out with 6-10 GPS  
> devices and a hill and see what the results are, I doubt you would  
> get any where near as accurate as you are assuming.


What kind of accuracy do you want? We are talking about people wanting  
to tag incline={up, down}. GPS elevation differences are certainly  
good enough to make that binary classification, especially if the  
incline is one that matters.

Should every sorry GPS trace be used? Perhaps as a quick-and-dirty  
start, but you are right, better and more accurate data is needed.  
People who care about these things in a particular area could  
certainly arrange to get accurate gpx data with an altimeter equipped  
GPS.

In addition, we have access to topographical data many places, a fact  
which has not been mentioned in this thread. This data can also be  
used to derive elevation gradients of roads.

I realize it wont be possible to compute elevation gradients tomorrow,  
but why not plan ahead? Who would've thought a few years ago that the  
project would be so far advanced? Wouldn't you rather have nodes on a  
way with "incline=7%" than "incline=up"? Wouldn't it be better to get  
this data from a database lookup than from manual tagging?

Cheers,
Morten





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