[GRASS-user] R: Re: Problems with r.surf.contour

[bianca.federici]

Thank you very much to both Markus! bianca 
Inviato dal mio dispositivo Samsung

-------- Messaggio originale --------
Da: Markus Neteler <neteler at osgeo.org> 
Data: 30/03/2017  22:11  (GMT+01:00) 
A: Markus Metz <markus.metz.giswork at gmail.com> 
Cc: Bianca Federici <bianca.federici at unige.it>, grass-user <grass-user at 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 at gmail.com> wrote:
> On Thu, Mar 30, 2017 at 3:48 PM, Bianca Federici <bianca.federici at 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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