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

[Anna Petrášová]

On Mon, Apr 19, 2021 at 10:24 AM Veronica Andreo <veroandreo at gmail.com>
wrote:

> [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.
>

Vero is right, I tested it and it does work as the manual describes, using
the values of categories in your case.

Anna

>
> All the best,
> Vero
>
> 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|cat
>> INTEGER|value
>> CHARACTER|label
>>
>> 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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