[GRASS-user] r.shaded.relief Output Question

[Carlos Grohmann]

Inverted relief on shaded maps (and also on aerial photos or satellite images) is called pseudoscopy. It's just an optical illusion. If you live on the northern hemisphere you are more 'used' to see images with illumination from the south (and vice-versa for southern hemisphere), so when you have illumination from north you see things 'inverted' (the same happens if you rotate 180 degrees a aerial photo or sat image).

To me, in Brazil, I use illumination from NW (315) or NE (045).  

cheers

Carlos

PS. Micha, when azimuth = 315 the sun is from North west




--  
Prof. Carlos Henrique Grohmann
Institute of Geosciences - Univ. of São Paulo, Brazil
- Digital Terrain Analysis | GIS | Remote Sensing -  

http://carlosgrohmann.com (http://carlosgrohmann.com/)
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On Friday, 23 March 2012 at 16:39, Micha Silver wrote:

> On 03/23/2012 09:29 PM, Micha Silver wrote:  
> > On 03/23/2012 08:31 PM, Rich Shepard wrote:  
> > > On Fri, 23 Mar 2012, Daniel Lee wrote:  
> > >  
> > >  
> > > > ... 235° would be ... from the southwest.  
> > >  
> > >   Yep. That's the way it usually works.  
> > >  
> >  
> > It's just an optical illusion. Rotate the PDF 90 deg to the right, and it looks "right". I usually choose azimuth=315 for r.shaded.relief. When the sun is from the NW, shadows appear "below" the features, and we visualize mountains as raised and valleys as lower.
> >   
> > HTH,
> > Micha
> >  
> Ooops, Correction: when azimuth=315 the sun is from the *South* West, producing naturally looking relief maps.
>  
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