<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<p>Dear Markus,</p>
<div class="moz-cite-prefix">Il 30/03/2017 15:35, Markus Metz ha
scritto:<br>
</div>
<blockquote
cite="mid:CAG+h=FGhOEUo8a2X+q9VKy3WY5KgAT88P97-isCVn=7dAkMFtw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>Dear Bianca,<br>
<br>
On Thu, Mar 30, 2017 at 10:37 AM, Bianca Federici <<a
moz-do-not-send="true"
href="mailto:bianca.federici@unige.it">bianca.federici@unige.it</a>>
wrote:<br>
><br>
> Dear Markus,<br>
><br>
> thank you very much for your suggestion... I never used
the option -a in g.region command!<br>
<br>
</div>
The -a flag for g.region ensures that the cell resolution is
exactly as given (5 meter in your case). That makes subsequent
calculations easier instead of having non-square cells. A
side-effect is that the region might be slightly enlarged in
order to get the desired resolution which in turn means that
the vector is fully covered.<br>
<br>
</div>
More important is that you set the region first, before you
rasterize the contour lines, and then don't change the region
any more.<br>
</div>
</blockquote>
I did it!<br>
<blockquote
cite="mid:CAG+h=FGhOEUo8a2X+q9VKy3WY5KgAT88P97-isCVn=7dAkMFtw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>><br>
> The results improved a lot, but some problems are still
present in the linear interpolation between two contour
levels.<br>
<br>
</div>
<div>r.surf.contour uses linear interpolation between contour
lines. That means there can be sudden changes in slope at
the location of contour lines. You can also try r.resamp.rst
or r.resamp.bspline to use spline interpolation which can
give you smoother surfaces.<br>
<br>
</div>
<div>The contour lines seem to be at 25 meter steps, that is
rather coarse. You could augment the contour lines with a
DEM, e.g. SRTM with a vertical resolution of 1 meter in
places with large gaps between contour lines, then
interpolate with r.resamp.rst or r.resamp.bspline.</div>
</div>
</div>
</blockquote>
The contour lines are quite coarse, and I can surely try to use
other interpolation methods... but the point is:<br>
r.surf.contour works well??? <br>
it's seems to me that no linear interpolation between two contour
levels is perfomed, in fact the slope is not constant between them
but increase until half the distance and then decrease, or
viceversa, instead of being constant.<br>
Or am I wrong?<br>
<br>
Thanks, <br>
Bianca<br>
<br>
<blockquote
cite="mid:CAG+h=FGhOEUo8a2X+q9VKy3WY5KgAT88P97-isCVn=7dAkMFtw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>> Here you may see the slope map and a slope profile
that enhance the not proper result:<br>
><br>
> <a moz-do-not-send="true"
href="https://www.dropbox.com/s/7olimii9s0m21rh/slope_contourlevel.PNG?dl=0">https://www.dropbox.com/s/7olimii9s0m21rh/slope_contourlevel.PNG?dl=0</a><br>
<br>
</div>
<div>That's the same image like in your first post?<br>
</div>
</div>
</div>
</blockquote>
No, it's not, it's a new one<br>
<br>
<br>
<blockquote
cite="mid:CAG+h=FGhOEUo8a2X+q9VKy3WY5KgAT88P97-isCVn=7dAkMFtw@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div><br>
</div>
<div>Markus M<br>
<br>
</div>
<div>><br>
> I hope that you or somebody else have other suggestions
;-)<br>
><br>
> Bianca<br>
><br>
><br>
> Il 27/03/2017 21:21, Markus Metz ha scritto:<br>
><br>
> g.region is a very powerful tool with sometimes
unexpected effects. See suggested workflow below.<br>
><br>
> On Mon, Mar 27, 2017 at 12:26 PM, Bianca Federici <<a
moz-do-not-send="true"
href="mailto:bianca.federici@unige.it">bianca.federici@unige.it</a>>
wrote:<br>
> ><br>
> > Dear all,<br>
> > I'm writing to report a problem I noticed using
r.surf.contour.<br>
> > I created a DTM from contour lines, but I notice
something a wrong behaviour of the r.surf.contour resulting
map.<br>
> ><br>
> > In detail I imported with v.in.ogr a shape file
describing contour lines every 25m of altitude<br>
> > 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.<br>
> > 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.<br>
> ><br>
> > 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:<br>
> > <a moz-do-not-send="true"
href="https://www.dropbox.com/s/7olimii9s0m21rh/slope_contourlevel.PNG?dl=0">https://www.dropbox.com/s/7olimii9s0m21rh/slope_contourlevel.PNG?dl=0</a><br>
> > Here you can see the DTM profile along the cross
section, that shows the irregular morphology of the created
DTM<br>
> > <a moz-do-not-send="true"
href="https://www.dropbox.com/s/useoxstmceyulk6/DTM_cross_section.PNG?dl=0">https://www.dropbox.com/s/useoxstmceyulk6/DTM_cross_section.PNG?dl=0</a><br>
> ><br>
> > I tested it in GRASS 6.4.4, 7.0.3 and 7.2.0,
working either in Windows and in Linux.<br>
> ><br>
> > I hope that the developers team could correct this
malfunction.<br>
> > Best regards,<br>
> > Bianca<br>
> ><br>
> > PS: The used commands:<br>
> > v.in.ogr ...<br>
> > g.region -p res=1<br>
> > v.to.rast input=contourlevel25m type=line
output=contourlevel25m use=attr column=ELEVATION<br>
> > g.region -p res=5<br>
> > r.surf.contour input=contourlevel25m
output=dtm_contourlevel25m<br>
> > r.slope.aspect elevation=dtm_contourlevel25m
slope=slope_contourlevel25m<br>
><br>
> Please try<br>
> v.in.ogr ...<br>
> g.region -p -a res=5 vect=contourlevel25m<br>
> v.to.rast ...<br>
><br>
> # do not change the region again<br>
> r.surf.contour ...<br>
><br>
> HTH,<br>
><br>
> Markus M<br>
><br>
><br>
> ><br>
> > --<br>
> > Eng. Bianca Federici, PhD<br>
> > Assistant Professor in Geomatics<br>
> ><br>
> > DICCA - Department of Civil, Chemical and
Environmental Engineering<br>
> > Laboratory of Geodesy, Geomatics and GIS<br>
> > University of Genoa<br>
> > Via Montallegro, 1 - 16145 Genova ITALY<br>
> > Phone: +39 010 353 2421 - Fax: +39 010 353 2546<br>
> > <a moz-do-not-send="true"
href="mailto:E-mail%3Abianca.federici@unige.it">E-mail:bianca.federici@unige.it</a>
-<a moz-do-not-send="true"
href="http://www.dicca.unige.it/geomatica/ricerca">www.dicca.unige.it/geomatica/ricerca</a><br>
> ><br>
> > Gter srl Innovation in Geomatics, Gnss and Gis<br>
> > Spin-off of the University of Genoa<br>
> > Piazza De Marini 3/61, 16123 Genova<br>
> > Phone: +39 010 8694830 - Fax: +39 010 8694737 -<br>
> > <a moz-do-not-send="true"
href="mailto:E-mail%3Ainfo@gter.it">E-mail:info@gter.it</a>
-<a moz-do-not-send="true" href="http://www.gter.it">www.gter.it</a><br>
> > <a moz-do-not-send="true"
href="http://www.facebook.com/Gteronline">www.facebook.com/Gteronline</a><br>
> > <a moz-do-not-send="true"
href="http://www.twitter.com/Gteronline">www.twitter.com/Gteronline</a><br>
> ><br>
> >
-----------------------------------------------------------------<br>
> > Please consider the environment before printing
this email!<br>
> ><br>
> > _______________________________________________<br>
> > grass-user mailing list<br>
> > <a moz-do-not-send="true"
href="mailto:grass-user@lists.osgeo.org">grass-user@lists.osgeo.org</a><br>
> > <a moz-do-not-send="true"
href="https://lists.osgeo.org/mailman/listinfo/grass-user">https://lists.osgeo.org/mailman/listinfo/grass-user</a><br>
><br>
><br>
</div>
</div>
</div>
</blockquote>
<br>
</body>
</html>