[OSM-talk] re contours

[Igor Brejc]

Hello,

To join this discussion: Kosmos uses smooth coloring of elevations, 
which I think gives better results than using fixed bands. I "borrowed" 
RGB values from this post, I think you should read it: 
http://www.perrygeo.net/wordpress/?p=7

The only drawback to this would probably be the fact that you need a 
greater color depth.
You can see a small sample of Kosmos relief rendering here: 
http://igorbrejc.net/wp-content/uploads/2008/02/crete.png

Igor

elvin ibbotson wrote:
> On 20 Mar 2008, at 10:05, Steve Hill wrote:
>
>> On Thu, 20 Mar 2008, elvin ibbotson wrote:
>>
>>> Treating contours as shape files seems to me to be heavy on storage, 
>>> downloads and processing. I have made a proposal in the wiki at 
>>> http://wiki.openstreetmap.org/index.php/Relief_maps#a_proposal to 
>>> use relief shading as a background to mapnik tiles. I'm sure there 
>>> must be good reasons not to do this and look forward to hearing them.
>>
>> I hadn't come across that proposal before, but my initial thoughts are:
>>
>> Coloured relief as described is good for an at-a-glance idea of the 
>> terrain, but (IMHO) are less useful when you want to look at the map 
>> in more detail.  It could be sensible to use this system on the 
>> low-zoom tiles and the switch to contour lines on the more detailed 
>> high-zoom ones.
>>
>> The proposed doubling of the intervals leaves them far too widely 
>> spaced at high altitudes which would render it more or less useless 
>> in mountainous terrain.  For example, a ski resort may have the town 
>> centre at 1100m and the top of the mountain at 3300m - on that map 
>> the only colours you will see are the 1024-2048m and 2048-4096m bands 
>> - 2 bands to cover up to 3000m of altitude difference is nowhere near 
>> enough to be useful.  On the whole I'm not convinced about reducing 
>> the band frequency with altitude anyway - if you're cycling (for 
>> example) at an altitude of 600m, a 100m high hill is just as 
>> significant to you as it would be if you were cycling at sea level, 
>> but in the former case it wouldn't show up on the map at all whilst 
>> in the latter it would be very obvious.
>
> I think, on balance, band width proportional to altitude makes a lot 
> of sense. A rise of a few metres makes a lot of difference  if you 
> live in a flood plain but is less significant when you're halfway up a 
> mountain. But, the proposal was just kite flying and if people think 
> the colour band approach is worth pursuing the banding and colours 
> wold need more thought. 1m band width near sea level is perhaps too 
> small while doubling each time is perhaps too exponential (though very 
> easy to code). More bands would help but would be counter-effective if 
> the colours became difficult to distinguish.
>
> elvin
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