[GRASS-user] Problems using v.surf.idw

Veronica Andreo veroandreo at gmail.com
Mon Apr 19 07:23:34 PDT 2021

[bringing the issue back to the list for reference]

Dear Luis,

Thanks for your feedback!

If you didn't provide a column name, and the module didn't fall back to the
cat column as it is supposed to, please report it as a bug (ideally with a
reproducible example). According to the manual and my very little
understanding of the c code, it should.

All the best,

El lun, 19 abr 2021 a las 16:00, Luí­s Moreira de Sousa (<
luis.de.sousa at protonmail.ch>) escribió:

> Hi Vero,
> from what I understand the module is seeking neither the value column, not
> the cat column. This map was created with r.to.vect, these are its
> attributes:
> > v.info -c soil_map_rcl_no_water
> Displaying column types/names for database connection of layer <1>:
> INTEGER|value
> If v.surf.idw was indeed seeking the cat column I would expect the module
> to succeed with this input, producing a nice Voronoi map.
> My suggestion would be to explicitly reference the name of the default
> column/attribute in the manual.
> Thank you.
> --
> Luís
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Monday, April 19, 2021 1:56 PM, Veronica Andreo <veroandreo at gmail.com>
> wrote:
> Dear Luis,
> El lun, 19 abr 2021 a las 8:45, Luí­s Moreira de Sousa via grass-user (<
> grass-user at lists.osgeo.org>) escribió:
>> Dear Anna,
>> thank you for the reply, indeed once I added the column parameter the
>> module completed successfully. The manual includes the following on this
>> parameter:
>>        column=name
>>            Name of attribute column with values to interpolate
>>            If not given and input is 2D vector map then category values
>> are used. If input is 3D vector
>>            map then z-coordinates are used.
>> If I read that correctly, the module should pick up the "value" column by
>> defualt. This particular layer was created by GRASS itself and includes a
>> "value" column:
> I might be biased, but the description is clear to me: provide the name of
> a column that contains the values/quantities that will be used to
> interpolate. If you do not provide a column name, cat will be used (i.e.,
> the IDs) in a 2D vector, or the z column in a 3D vector.
>> >  v.info -c soil_map_rcl_no_water
>> Displaying column types/names for database connection of layer <1>:
>> INTEGER|cat
>> INTEGER|value
>> CHARACTER|label
>> It is now clear this is not the case, `v.surf.idw` is seeking another
>> column by default, one that is not created by vector creating modules.
> It does not seek for another column, it defaults to cat if you do not
> provide a column name where the variable you want to interpolate is. It
> would be annoying, IMO, if I was forced to name a column `value` just
> because a module only takes that name. Also, there might be many columns
> with quantities/values in the attr table of a vector. How is the module
> supposed to know which one to use, if the user does not provide a name?
> Perhaps this could be made more explicit in the manual page.
> Maybe the fact that value appears in the description and your column is
> called value triggered the confusion?
> We really appreciate any suggestions on how to improve the wording to make
> it clearer.
> Best,
> Vero
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