[GRASS-user] Problems using v.surf.idw
kratochanna at gmail.com
Mon Apr 19 07:53:30 PDT 2021
On Mon, Apr 19, 2021 at 10:24 AM Veronica Andreo <veroandreo at gmail.com>
> [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.
> 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
>> > v.info -c soil_map_rcl_no_water
>> Displaying column types/names for database connection of layer <1>:
>> 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.
>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>> On Monday, April 19, 2021 1:56 PM, Veronica Andreo <veroandreo at gmail.com>
>> 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
>>> 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>:
>>> 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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