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

Veronica Andreo veroandreo at gmail.com
Mon Apr 19 04:56:42 PDT 2021

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|value
> 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.

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