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List: grass-user
Subject: [GRASS-user] R: Re: Problems with r.surf.contour
From: "bianca.federici" <bianca.federici () unige ! it>
Date: 2017-03-30 20:39:01
Message-ID: didpd4jr3oriby6k8d9npemj.1490906341863 () email ! android ! com
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Thank you very much to both Markus! bianca
Inviato dal mio dispositivo Samsung
-------- Messaggio originale --------
Da: Markus Neteler <neteler@osgeo.org>
Data: 30/03/2017 22:11 (GMT+01:00)
A: Markus Metz <markus.metz.giswork@gmail.com>
Cc: Bianca Federici <bianca.federici@unige.it>, grass-user <grass-user@lists.osgeo.org>
Oggetto: Re: [GRASS-user] Problems with r.surf.contour
Dear Bianca,
On Thu, Mar 30, 2017 at 5:27 PM, Markus Metz
<markus.metz.giswork@gmail.com> wrote:
> On Thu, Mar 30, 2017 at 3:48 PM, Bianca Federici <bianca.federici@unige.it>
...
>> The contour lines are quite coarse, and I can surely try to use other
>> interpolation methods... but the point is:
>> r.surf.contour works well???
>
> I don't think so.
Yes, there are much better methods than r.surf.contour.
See also here:
https://grasswiki.osgeo.org/wiki/Contour_lines_to_DEM
markusN
>> 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.
>
> There are indeed strange patterns in the slope values between contour lines.
> The used distance to the second contour is not the shortest distance to the
> second contour, that is a bug. The distance calculation is unusual, it is
> not euclidean and not manhattan distance, no idea what kind of distance this
> is.
>
> Apart from that, I would not use linear interpolation to create a surface
> from contour lines but use one of the previously mentioned r.resamp.*
> modules. And r.surf.contour is incredibly slow.
>
> Markus M
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<html><head><meta http-equiv="Content-Type" content="text/html; \
charset=UTF-8"></head><body>
<div>Thank you very much to both \
Markus! </div><div>bianca </div><div><br></div><div \
id="composer_signature"><div style="font-size:85%;color:#575757">Inviato dal mio \
dispositivo Samsung</div></div><br><br>-------- Messaggio originale --------<br>Da: \
Markus Neteler <neteler@osgeo.org> <br>Data: 30/03/2017 22:11 (GMT+01:00) \
<br>A: Markus Metz <markus.metz.giswork@gmail.com> <br>Cc: Bianca Federici \
<bianca.federici@unige.it>, grass-user <grass-user@lists.osgeo.org> \
<br>Oggetto: Re: [GRASS-user] Problems with r.surf.contour <br><br>Dear \
Bianca,<br><br>On Thu, Mar 30, 2017 at 5:27 PM, Markus \
Metz<br><markus.metz.giswork@gmail.com> wrote:<br>> On Thu, Mar 30, 2017 at \
3:48 PM, Bianca Federici <bianca.federici@unige.it><br>...<br>>> The \
contour lines are quite coarse, and I can surely try to use other<br>>> \
interpolation methods... but the point is:<br>>> r.surf.contour works \
well???<br>><br>> I don't think so.<br><br>Yes, there are much better methods \
than r.surf.contour.<br><br>See also \
here:<br>https://grasswiki.osgeo.org/wiki/Contour_lines_to_DEM<br><br>markusN<br><br>>> \
it's seems to me that no linear interpolation between two contour levels<br>>> \
is perfomed, in fact the slope is not constant between them but increase<br>>> \
until half the distance and then decrease, or viceversa, instead of being<br>>> \
constant.<br>><br>> There are indeed strange patterns in the slope values \
between contour lines.<br>> The used distance to the second contour is not the \
shortest distance to the<br>> second contour, that is a bug. The distance \
calculation is unusual, it is<br>> not euclidean and not manhattan distance, no \
idea what kind of distance this<br>> is.<br>><br>> Apart from that, I would \
not use linear interpolation to create a surface<br>> from contour lines but use \
one of the previously mentioned r.resamp.*<br>> modules. And r.surf.contour is \
incredibly slow.<br>><br>> Markus M<br></body></html>
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