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
<[email protected] <mailto:[email protected]>> 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
>
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> Laboratory of Geodesy, Geomatics and GIS
> University of Genoa
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> Phone: +39 010 353 2421 - Fax: +39 010 353 2546
> E-mail:[email protected]
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