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

[Mark Williams]

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Andy Allan wrote:
> On Mon, Sep 15, 2008 at 11:08 PM, David Earl <david at frankieandshadow.com> wrote:
>> On 15/09/2008 22:07, Donald Allwright wrote:
>>> The theory is that
>>> if the SRTM data include an altitude reading for the lake itself (I
>>> haven't actually checked this yet!), I should be able to use an approach
>>> similar to what you suggest to get a much more accurate map. The holy
>>> grail would be to be able to click somewhere within a lake, and the
>>> software to automatically generate a perimeter. However I suspect that
>>> will be a long way off, if it ever happens.
>> But will the accuracy be any better? SRTM seems to be 3 arc seconds
>> outside the USA = approx 90m of latitude per pixel.
> 
> Absolutely. I can see the idea, but if there's Yahoo or even Landsat
> imagery it'll most likely be more accurate that way to get lakes.
> 
> And don't be fooled by the contours on the cycle map - they might be
> thin and look really accurate, but they are just massive
> extrapolations from relatively low-resolution DEMs. Most lakes have
> one or two contours running underneath them at the moment, some rivers
> run uphill in some places (especially in narrow gorges) and so on.
> 
> Cheers,
> Andy
> 
> _________

Absolutely agree - I live near the hill in Essex (OK, there's 2..) &
SRTM has it quite badly wrong, both height & just where the highest
point is - by around a mile. Any lakes generated from that would be,
well, unpredictable!

Given how flat the surrounding area is I found that quite disappointing.

Mark

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