Hi Francesco,
On 13/11/18 05:57, francesco sapienza wrote:
Hello! i'm trying to validate my IDW model for field values of pH (and
other parameters) using the following:
|# Partition sample points in 4 groups Module("v.kcv", map="pHsr",
npartitions=4, column="part")|
|Module("v.extract", flags="r", input="pHsr", output="pHcalibration",
where="part=1")
> Module("v.extract", input="pHsr", output="pHvalidation",
where="part=1")|
You probably want to change your part=1 to something else in one of
these calls.
|Module("v.surf.idw", input="pHcalibration", column="pH_values",
npoints=12, power=2, output="pH_CAL_idw")|
|Module("v.what.rast", map="pHvalidation", raster="pHsr",
column="actual") Module("v.what.rast", map="pHvalidation",
raster="pH_CAL_idw", column="Estimated")|
Things work pretty good so far, i obtained a vector with the actual
values and the estimated ones, the next step would be to evaluate the
root mean square error for this routine.
Calculating something like the RMSE is actually quite easy, with no need
to use any SQL:
- Create a new column squared error, type double precision, with
v.db.addcolum
- Fill it using v.db.update using qcol="(estimated - actual)*(estimated
- actual)"
- Extract aggregated stats on that column using v.univar
- calculate the square root of the mean value to get RMSE
(You could also just get the mean of the absolute values of a column
containing simply (estimated - actual).)
(Eventually i also want to loop
the idw estimation for different set of Validation and Calibration groups).
*So far i haven't used the script but instead i used the GUI interface
for every single comand (v.kcv, v.extract, v.surf.idw and v.what.rast).*
For the following section i wanted to use a script but i have trouble
working it, as stats is 'not defined'.
|sqlstat = "SELECT actual,estimated FROM pHvalidation" stats =
Module("db.select", flags="c", sql=sqlstat, stdout_=PIPE).outputs.stdout
stats = stats.replace("\n", "|")[:-1].split("|") stats =
(np.asarray([float(x) for x in stats], dtype="float").
reshape(len(stats)/2, 2))|
rsme=np.sqrt(np.mean(np.diff(stats,axis=1)**2))
I tried to run the GUI for db.select specifing in the sql SELECT= SELECT
actual,estimated FROM pHvalidation".
I obtained in the output of the GUI the right selected values, but i
don't know how to procede calculating the RMSE value, when i try to run
the script above, stats stay as 'not defined'.
I don't think you're using Module as expected. Please read [1]. AFAIR,
Modules.outputs is a dictionary of the modules' output parameters, not
the output of the module run.
Moritz
[1] https://grass.osgeo.org/grass74/manuals/libpython/pygrass_modules.html
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