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

Micha Silver micha at arava.co.il
Mon Sep 20 08:30:02 EDT 2010

On 20/09/2010 12:32, nunosousa84 wrote:
> Thank you all. Well i have some news. Hamish i have followed your suggestion
> of using the mapcalc commands. For all this steps i worked directly through
> GRASS 6.4 0RC6 and not QGIS. I have opened the grass raster layer with the
> contours (lines) and applyed the commands suggested:
> http://grass.osgeo.org/wiki/Contour_lines_to_DEM
> The result was this:
> http://osgeo-org.1803224.n2.nabble.com/file/n5549840/shadedtest1.jpg
> Well it seems the terrace effect desappeared but there are some glintches,
> do you think its normal?
> Concerning the flat mesa tops they look really ugly, any suggestion how to
> remake/remodel them? I suppose i have to go to the original geotiff
> topography chart and remake some vector lines to overcome that problem? What
> should i do?
> About the blackspots and the color table im not sure but changing it doesnt
> overcome the problem, the spots remain the same. Here it is the r.univar
> report of the shadedrelief layer:
> "total null and non-null cells: 2256660
> total null cells: 6164
There must be your black spots. But why you are getting null values, I 
can't say. Is it possible that you have accidentally made some contour 
lines that cross or touch?
> 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"
> Now to the strange issue (QGIS Shaded Relief Plugin). Remember the error i
> posted earlier? Well it seems i was able to work with that plugin but only
> after i run the surf contour layer in GRASS. Let me explain i redone the
> steps decribed before as suggested by Hamish (mapcalc, surfcontour,etc...),
> all in GRASS 6.4 0RC6. Then changed to QGIS, opened the layer just made in
> GRASS and run the QGIS Shaded Relief Plugin. Now it worked.
> About the Region Settings they were set in QGIS. Since the region im working
> is fairly small i used this parameters: N-S Res = 1.00014 and E-W Res =
> 1.00024 (I think this is the minimum resolution supported). One problem i
> noticed and it might be a QGIS bug is that everytime i open QGIS or add a
> layer it resets the projection/coordination values (For example im using
> Datum ED50 UTM zone 29 international ellipsoid but when i open a layer or
> QGIS it always resets this values to others). Maybe i should save this
> parameters directly in GRASS? My dificulty is how, there are so many
> commands for a begginer :-)
> Regards and thank you
>    Nuno

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

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