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

[Keith Sharp]

On Mon, 2008-09-15 at 11:24 +0100, Steve Hill wrote:
> 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. :)

I considered something similar to mapping lakes and lochs - use my GPS
with barometric altimeter to measure the elevation of the surface of the
water and then use the SRTM data to work out the contour that
corresponds to the edge of the water.  Hey presto, instant loake or loch
map!

I never got round to implementing anything because I discovered most of
the bodies of water in Scotland had been mapped.

Keith.