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

[Luí­s Moreira de Sousa]

Dear all,

I opened a new issue with a simple example:
https://github.com/OSGeo/grass/issues/1547

Thank you for the replies.

--
Luís

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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Monday, April 19, 2021 4:53 PM, Anna Petrášová <kratochanna at gmail.com> wrote:

> 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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