[GRASS-user] Problems with r.surf.contour

[Bianca Federici]

Dear Markus,

thank you very much for your suggestion... I never used the option -a in 
g.region command!

The results improved a lot, but some problems are still present in the 
linear interpolation between two contour levels.

Here you may see the slope map and a slope profile that enhance the not 
proper result:

https://www.dropbox.com/s/7olimii9s0m21rh/slope_contourlevel.PNG?dl=0

I hope that you or somebody else have other suggestions ;-)

     Bianca


Il 27/03/2017 21:21, Markus Metz ha scritto:
> g.region is a very powerful tool with sometimes unexpected effects. 
> See suggested workflow below.
>
> On Mon, Mar 27, 2017 at 12:26 PM, Bianca Federici 
> <bianca.federici at unige.it <mailto:bianca.federici at unige.it>> wrote:
> >
> > Dear all,
> > I'm writing to report a problem I noticed using r.surf.contour.
> > I created a DTM from contour lines, but I notice something a wrong 
> behaviour of the r.surf.contour resulting map.
> >
> > In detail I imported with v.in.ogr a shape file describing contour 
> lines every 25m of altitude
> > Then, I converted in raster (setting a resolution of the 
> computational region equal to 1m), and created the DTM ( setting a 
> resolution of the computational region equal to 5m) with r.surf.contour.
> > Either plotting a profile of the DTM and creating the slope map 
> (with r.slope.aspect), it's evident that r.surf.contour works bad.
> >
> > Here you can see the slope map, with the contour level in black, and 
> the position of the extracted cross section; you may notice artificial 
> steps mainly in corrispondence of the contour levels, instead of 
> uniform slopes:
> > https://www.dropbox.com/s/7olimii9s0m21rh/slope_contourlevel.PNG?dl=0
> > Here you can see the DTM profile along the cross section, that shows 
> the irregular morphology of the created DTM
> > https://www.dropbox.com/s/useoxstmceyulk6/DTM_cross_section.PNG?dl=0
> >
> > I tested it in GRASS 6.4.4, 7.0.3 and 7.2.0, working either in 
> Windows and in Linux.
> >
> > I hope that the developers team could correct this malfunction.
> > Best regards,
> >     Bianca
> >
> > PS: The used commands:
> > v.in.ogr ...
> > g.region -p res=1
> > v.to.rast input=contourlevel25m type=line output=contourlevel25m 
> use=attr column=ELEVATION
> > g.region -p res=5
> > r.surf.contour input=contourlevel25m output=dtm_contourlevel25m
> > r.slope.aspect elevation=dtm_contourlevel25m slope=slope_contourlevel25m
>
> Please try
> v.in.ogr ...
> g.region -p -a res=5 vect=contourlevel25m
> v.to.rast ...
>
> # do not change the region again
> r.surf.contour ...
>
> HTH,
>
> Markus M
>
>
> >
> > --
> > Eng. Bianca Federici, PhD
> > Assistant Professor in Geomatics
> >
> > DICCA - Department of Civil, Chemical and Environmental Engineering
> > Laboratory of Geodesy, Geomatics and GIS
> > University of Genoa
> > Via Montallegro, 1 - 16145 Genova ITALY
> > Phone: +39 010 353 2421 - Fax: +39 010 353 2546
> > E-mail:bianca.federici at unige.it 
> <mailto:E-mail%3Abianca.federici at unige.it> 
>  -www.dicca.unige.it/geomatica/ricerca 
> <http://www.dicca.unige.it/geomatica/ricerca>
> >
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