[Tagging] Feature proposal - RFC - natural=ridge

Arne Johannessen arne at johannessen.de
Mon Nov 14 11:17:31 GMT 2011


Nathan Edgars II wrote:
> On 11/8/2011 2:03 PM, John F. Eldredge wrote:
>> Nathan Edgars II<neroute2 at gmail.com>  wrote:
>>> 
>>> What I mean is that if the ridges can be auto-generated, they can be
>>> rendered without being in the database.

They can't be auto-generated from gridded DEMs. Consider these neighboured elevation grid points as an example:

200   213
    ?
210   196

It's impossible to tell if the altitude in the centre is more like 212 (creating a SW-NE ridge) or more like 198 (creating a saddle with a NW-SE mountain pass). In any event, the "ridges" created from such gridded data would have a jagged zigzag form which would neither be correct nor pleasing to the eye.

As far as DEMs go, you need additional data besides grid or spot elevations to fully represent the terrain. This includes skeleton lines (ridges and streams) and cliffs. Since we map streams and cliffs as a matter of course, there's no reason not to do the same with ridges.

The main problem really is getting an exact position for those features. Might be rather difficult in many cases (incorrect Bing imagery in mountainous terrain, dangerous cliffs prevent you from surveying by GPS, ...).


>> What data source are you suggesting that the renderer should use, if not the OSM database?
> 
> The same one that the cycle map layer uses to draw contour lines.

As Lauri already noted, those are too coarse to be of much use for skeleton lines in large scales (beyond zoom level 10 or so).

Regards,
Arne

-- 
Arne Johannessen




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