[GRASS-user] Re: QGIS GRASS plugin shadedrelief issue

Micha Silver micha at arava.co.il
Thu Sep 23 16:02:17 EDT 2010

On 09/23/2010 06:46 PM, nunosousa84 wrote:
> yes you're right, my distraction. Well i was able to work it out much more
> relaxed now :-) I still think the results from the shaded relief are a bit
> odd. For example if use 130º azimuth the river valleys appears above the
> near mountains, but if i use degrees between 270 and 0º or between 0 and 90º
> the river valleys appear below the rest like it should be. Is it normal? I
We're used to perceiving shadows below and highlights above what is 
being lit. The same holds for a hill-shaded terrain. When we see shadows 
on a slope, it seems to be south facing, and highlights appear north 
facing. So if you "place" the sun at 130° (SE) then you are lighting the 
south facing slope, and making it appear north facing, thus causing the 
valleys to appear to be hills, and the peaks appear as valleys. We have 
a set of ortho-photos that were shot early in the morning (sun in the 
east) and a colleague always turns the maps "upside down" (N pointing 
down) so that the hills and valleys look right.
The most "natural" looking hillshading is with azimuth between 270 - 
315° (W to NW).
> will try to post a picture here. Im a bit concerned about this cause i will
> create the hidrographic system also (basins, ...). By the way GRASS as any
> map composer like QGIS to be able to finish the work (put scale bar, north,
> legend, title,...)?
Yes, QGIS is a good choice. GRASS does have a full set of map composer 
tools, but some graphic elements require a bit more fiddling to get them 
right. Mind you, the results can be quite rewarding.

Micha Silver
Arava Development Co. +972-52-3665918

More information about the grass-user mailing list