v.surf.idw broken

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v.surf.idw broken

Jachym Cepicky
Hi,
I can not get reasonable result (compared with v.surf.rst) from
v.surf.idw using attached input vector points

is it possible, that v.surf.idw is kind of broken?

[xy location]

v.in.ogr dsn=vzorky.shp out=vzorky

v.surf.idw in=vzorky out=dpidw column=dp
v.surf.rst in=vzorky elev=dprst zcolumn=dp

thanks

jachym
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e-mail: jachym.cepicky gmail com
URL: http://les-ejk.cz
GPG: http://les-ejk.cz/pgp/JachymCepicky.pgp

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Re: v.surf.idw broken

Paul Kelly
On Tue, 13 Apr 2010, Jachym Cepicky wrote:

> Hi,
> I can not get reasonable result (compared with v.surf.rst) from
> v.surf.idw using attached input vector points
>
> is it possible, that v.surf.idw is kind of broken?

Hello,
I can confirm that I can reproduce the strangeness, that it only happens
when *not* using the -n flag (i.e. when indexing points) and that it
happens when interpolating a relatively small number of points into a
region with a relatively high resolution. E.g. for the given data I
observe strangeness for a resolution of 10, but it goes away either by
specifying the -n flag or decreasing the resolution to 15.

It does indeed look to be caused by my buggy code from 2003, or (perhaps
less likely; I'm not sure) some later change to it - specifcally something
to do with the "shortlist" method of avoiding an intensive search for
nearby sites/points when the number of points is relatively small compared
to the region size.

I can't see anything obviously wrong but I'll look into it over the next
few days...

Paul
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Re: v.surf.idw broken

Jachym Cepicky
Thanks

I can confirm, that using -n flag works

Jachym

2010/4/13 Paul Kelly <[hidden email]>:

> On Tue, 13 Apr 2010, Jachym Cepicky wrote:
>
>> Hi,
>> I can not get reasonable result (compared with v.surf.rst) from
>> v.surf.idw using attached input vector points
>>
>> is it possible, that v.surf.idw is kind of broken?
>
> Hello,
> I can confirm that I can reproduce the strangeness, that it only happens
> when *not* using the -n flag (i.e. when indexing points) and that it happens
> when interpolating a relatively small number of points into a region with a
> relatively high resolution. E.g. for the given data I observe strangeness
> for a resolution of 10, but it goes away either by specifying the -n flag or
> decreasing the resolution to 15.
>
> It does indeed look to be caused by my buggy code from 2003, or (perhaps
> less likely; I'm not sure) some later change to it - specifcally something
> to do with the "shortlist" method of avoiding an intensive search for nearby
> sites/points when the number of points is relatively small compared to the
> region size.
>
> I can't see anything obviously wrong but I'll look into it over the next few
> days...
>
> Paul
>



--
Jachym Cepicky
e-mail: jachym.cepicky gmail com
URL: http://les-ejk.cz
GPG: http://les-ejk.cz/pgp/JachymCepicky.pgp
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