[OSM-talk] OpenPisteMap: Cross Country Ski Trails.

[Steve Hill]

On Mon, 2 Mar 2009, Simon Wood wrote:

> I have tagged the trails a 'highway=footway' and 'piste:type=nordic' as 
> these trails are multi-use; cycling and walking in the summer and 
> groomed cross country trails in the winter.
>
> At present OPM does not render these as ski-trails. Is this the correct 
> way to tag this situation, or can someone suggest a better method?

At the moment, OPM only renders alpine (downhill) pistes.  Other types of 
piste are on the (ever lengthening :) todo list.  I think the rendering 
styles need a fairly major overhaul before I go much further with adding 
more features though.

> Also there is no mention of the following on the OpenPisteMap wiki page 
> (http://wiki.openstreetmap.org/index.php/Proposed_features/Piste_Maps):
>
> 1) Direction of Way: I assume that 'forward' is meant as 'generally 
> downhill' as the 'piste:type=downhill' implies one-way.

Certainly for alpine pistes the way should go down hill and we assume 
they are one-way so the direction arrow rendered on the map points down 
hill.  For most alpine pistes this is going to be the normal state of 
affairs, although there are a few notable exceptions, such as some flat 
sections where it should probably be explicitly set to oneway=no.

For nordic routes, I guess things aren't quite so clear cut.  I don't 
really have any experience with nordic routes so I'm going to avoid 
commenting too much on this. :)

> 2) Steep Sections: Is there a method of marking a steep section? The 
> maps posted on site 
> (http://www.crowsnestguide.com/allisonwonderlands/allisonmap.html) draw 
> a little '|---' line next to the trail at the appropriate places. This 
> could be marked with a short way marked 'piste:steep=yes'. Where this is 
> against the general direction of the way should we reverse the way or 
> use a 'up/down' or 'forward/backward' tagging (ie. 
> 'piste:steep=backward')?

Whether a piste is "steep" is pretty subjective and more or less covered 
by the "piste:difficulty" tag.  Ok, so the difficulty covers other stuff 
like narrowness, moguls, etc. but I still don't think we want a subjective 
"steep" boolean attribute.  A non-subjective "incline=30%" type tag would 
be better, and matches up with what is often used on highways: 
http://wiki.openstreetmap.org/wiki/Proposed_features/Incline

> I would like to add a 'ele=xxx' tag to the markers tag at the junction 
> of the trails to give some indication of height gain/loss between 
> markers. This would enable a person unfamiliar with the trail to gain a 
> sense of the workout they are about to get....

I think using gps elevation data for this purpose would be a very bad idea 
due to the inaccuracy.  GPS elevation data can easilly be over 100 metres 
out, and that kind of inaccuracy would produce very different inclinations 
of the tracks.  The _differences_ in heights between 2 points might be 
reasonably accurate if they are taken by the same GPS receiver at a 
similar time, but once you start combining elevation data from many 
different receivers over a period of months or years I think the data will 
be worse than useless.

Even though the SRTM3 data is reasonably low-res, I think it would be 
better to use that rather than GPS elevation data.  The problem with SRTM3 
is that it doesn't cover high latitudes.  I'm certainly opposed to adding 
an "ele=" tag containing data that is known to be extremely inaccurate 
anyway.

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence