[OSM-talk] Own maps with hill shading and routes using mapnik

[Steve Hill]

On Sun, 14 Sep 2008, Andy Allan wrote:

> Big voids, e.g. the alps, can't just be "smoothed" over.

I wonder if the elevation data stored in OSM for various mountain summits 
might be useful for filling in small voids around the top of mountains. 
It doesn't help with missing vallies though.  e.g. where one side of the 
mountain is missing, the missing data could be interpolated between the 
known data at the edges of the void and the height of the summit.  It 
could go very wrong if the SRTM data doesn't closely match the OSM data 
though.

> If you have all the rivers you can constrain your filling
> algorithms to make sure the resultant landscape involves the rivers
> going downhill! So we've looked at how the river coverage in OSM
> compares to the voids, but at the moment they don't overlap so it's
> not much help to us.

Sounds like an interested approach, and something that can probably be 
automated relatively successfully, although I can't think how you would 
determine the elevation of the bottom of the valley if you were missing 
that data.  Maybe just extrapolate from the nearby gradients that are 
known.

Whatever the method used, it sounds like there could be a lot of 
corner-cases where the algorithm could produce crazy data which would 
need to be trapped. :)

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

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence