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

[Markus Metz]

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>
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  -www.dicca.unige.it/geomatica/ricerca
>
> Gter srl Innovation in Geomatics, Gnss and Gis
> Spin-off of the University of Genoa
> Piazza De Marini 3/61, 16123 Genova
> Phone: +39 010 8694830 - Fax: +39 010 8694737 -
> E-mail:info at gter.it  -www.gter.it
> www.facebook.com/Gteronline
> www.twitter.com/Gteronline
>
> -----------------------------------------------------------------
> Please consider the environment before printing this email!
>
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20170327/072ca38c/attachment.html>