[GRASS-user] log function for SQLite

[Nikos Alexandris]

NikosAlexandris wrote:
>>>>>>> Dear list,
>>>>>>> where is the extension for SQLite that contains the (mathematical) log
>>>>>>> function available to download?  As referenced in
>>>>>>> https://grass.osgeo.org/grass73/manuals/v.db.update.html.

Helmut Kudrnovsky:

>>>>>>> I think the reference in the manual requires a source or a link to it.
>>>>>> just found something in the wiki:
>>>>>> https://grasswiki.osgeo.org/wiki/Build_SQLite_extension_on_windows

Nikos:

>>>> For Linux:
>>>> gcc extension-functions.c -fPIC -shared -o libextensionfunctions.so
>>>> Note,
>>>> 1) there is still a "compile" warning for the code (no time to hunt)
>>>> 2) The log() function does not like, naturally, 0 values. But this can
>>>> be workedaround with a where SQL clause.
>>>> Can we not integrate this into GRASS?  It feels awkward to have to spend
>>>> so much time for a log or similar function to use in a v.db.update call.

Moritz:

>>> -1
>>>
>>> I don't think we should start interalizing solutions to issues related
>>> to database backend choice.

Nikos:

>> We can of course integrate a log and an "sqrt" function for v.db.update,
>> right?

Moritz:

>You mean within the v.db.update code ? But why log and sqrt and not others ?
>As said, I don't think we should go down that road.

You mean to say also no in intgrating, yes, in v.db.update some "common"
functions?  Why not?  Log and SqRt are just common functions.  We have
all of the basic descriptive statistics and we can do pretty much
everything with mapcalc.  Why not so for vector attributes, independent
from tha backend?

If there is no complication in integrating in v.db.update some math,
then why not use all of the math functions defined in the contributed
library for sqlite?

Note, d.vect has an "-r" flag. I want to get these values in a new
column, so I can share the vector and this sqrt-ed attribute outside of
GRASS.

Cheers, Nikos