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List:       grass-user
Subject:    Re: [GRASS-user] Problems with r.surf.contour
From:       Markus Neteler <neteler () osgeo ! org>
Date:       2017-03-30 20:11:25
Message-ID: CALFmHhvODCNzGa3SW=K=DytNs4nG0unqiMGMuAhREtRjst8Qjg () mail ! gmail ! com
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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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