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

[Micha Silver]

On 09/20/2010 06:18 PM, nunosousa84 wrote:
> Here are the results:
>
> http://osgeo-org.1803224.n2.nabble.com/file/n5551158/cleanresult.jpeg
>
> Well im not sure but at first glance doesnt seem to have much relation. This
> vector points layer that appear after runing the v.clean command shows also
> possible duplication of lines or just crossing lines? I have made a zoom to
> the vector lines where those 11 vector points are located and dont seem to
> recognize the problem.
>    
If digitizing was done without snapping, then there might be very small 
overshoots which v.clean has caught. But you're right that there doesn't 
seem to be any connection to the black spots in the shaded relief. In 
any case you might recreate the DEM using r.surf.contour with the 
cleaned vector contour layer.

As for the null values in the shaded relief, they should not be there.  
I can't see, in the r.shaded.relief script any way for NULL values to 
sneak in other than from cells with slope of 90 deg. Someone with a 
better understanding of the r.shaded.relief algorithm will have to pitch 
in...

If you want to continue with this, perhaps run r.slope.aspect on the DEM 
to get a slope raster, and check (r.univar again) what the min and max 
slope values are, and where, if any, you are getting 90° slope.
-- 
Micha

> Here goes the comparation results for both r.surf.contour layer and shaded
> relief layer, using the r.univar query:
>
> (surfcontour layer)
>
> total null and non-null cells: 2256660
> total null cells: 0
> Of the non-null cells:
> ----------------------
> n: 2256660
> minimum: 430
> maximum: 760
> range: 330
> mean: 541.46
> mean of absolute values: 541.46
> standard deviation: 66.726
> variance: 4452.36
> variation coefficient: 12.3234 %
> sum: 1221890343.312690258
>
> ---------------------------//------------------------
> (shadedrelief layer)
>
> total null and non-null cells: 2256660
> total null cells: 6164
> Of the non-null cells:
> ----------------------
> n: 2250496
> minimum: -75.1119
> maximum: 100
> range: 175.112
> mean: 42.1701
> mean of absolute values: 48.816
> standard deviation: 35.304
> variance: 1246.37
> variation coefficient: 83.718 %
> sum: 94903752.6220222563
>
> It seems only when i run the command shaded relief that null cells appears.
> Is it normal?
>
>    


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