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

[Micha Silver]

On 20/09/2010 23:39, nunosousa84 wrote:
> Thank you Micha. Just to confirm that the output of slope module is:
>
> total null and non-null cells: 2256660
> total null cells: 6164
>    
These null cells should be *only* around the edges, where there is not a 
3X3 window to calculate the slope. By default they'll show in an orange 
color in the display.
> Of the non-null cells:
> ----------------------
> n: 2250496
> minimum: 0
> maximum: 78.8343
> range: 78.8343
>    
That's a pretty steep maximum slope. 78% slope is almost vertical.  I 
wonder if the black spots are just very dark- that is points with a very 
steep slope, i.e. a cliff, that correctly show in a dark shade?
Again these might be some misses in the digitizing process.
> mean: 29.4765
> mean of absolute values: 29.4765
> standard deviation: 17.1799
> variance: 295.148
> variation coefficient: 58.2834 %
> sum: 66336658.9338117689
>
> I dont know maybe there is something wrong with my digitizing. Besides this
> problem do you think the result of the shaded relief command is acceptable?
>    
Well, that you'll have to say. You can improve the "mesa tops" effect by 
adding point altitudes to the contour vector at the peaks. See the 
manual page, and Hamish's explanation earlier.
> I dont know but it seems some parts of the map reveals some geometric
> artifacts, sometimes cutting through.
>    


-- 
Micha Silver
http://www.surfaces.co.il/
Arava Development Co.  +972-52-3665918