[OSM-dev] Shaded relief in OSM

[Artem Pavlenko]

On 6 Dec 2007, at 14:45, David Earl wrote:

> On 06/12/2007 13:51, Artem Pavlenko wrote:
>> Yes, this is my feeling as well. The resolution is no good for  
>> high  zoom levels.
>> Maybe we should look into creating our own relief maps, specially   
>> tailored to the OSM.
>
> One thought I had was that at high zooms an absolute relief map  
> isn't much help. You can have relatively flat high or low areas. If  
> you want a feel for what the landscape looks like, you need a  
> relative relief map at somewhat higher vertical resolution. But  
> then how do such things join up as you pan, and avoid having an  
> area of constant colour that could either be the flank of a hill at  
> right angles to the "light source" or a local plateau.
>
> I was thinking one could analyse the absolute relief data with a  
> pixel filter so that each pixel gets shaded according to a  
> difference function between its altitude and that of all the other  
> pixels in the filter (say the neighbouring 10 x 10 grid). You'd end  
> up with a vector whose direction gives the direction of fall at the  
> point, and whose length indicates how extreme the gradient is. If  
> say one used for a shade of green and the other combined with the  
> light source direction to give a shade of gray you might just get a  
> useful result which shows the local terrain independent of absolute  
> altitude.
>

Yep, I see your point about relative relief. We need some tools for  
experimenting...

Opps, got to run to pick up my son from school. Nice cycling map btw!
> Of course, we have none of these issues in Cambridge because it is  
> flat :-) Even Castle Hill might only just show up in a relative  
> relief map.
>



> David