* Moritz Lennert <[email protected]> [2017-03-09 19:07:21 +0100]:
Le 9 mars 2017 19:01:32 GMT+01:00, Nikos Alexandris <[email protected]>
a écrit :
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?
Moritz
The difficulty is not the functions as such, but the parser you need to
interpret what the user writes.
I see.
But hey, if you want to go down that road, go ahead. I just don't think
that compiling the functions once for SQLite is such a hassle as to
make worthwhile...
This is not easy for everyone though.
Nikos
[rest deleted]
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