5

I want to sum the cell values from 3 grids. I have a list of file paths (temp layers) generated in a "for" loop, looking like the following one. I cannot understand why the function makes some transformations and takes 7 input grids, when it should load and sum 3 grids.

If I sum these files in SAGA GUI, the result is the expected one. But when I sum the files using PyQGIS, the last raster is summed 7 times (see the end of the log).

Can anyone help me?

Here is my code:

s1 = "E:/rcal/OUTPUT11.sdat"
s2 = "E:/rcal/OUTPUT22.sdat"
s3 = "E:/rcal/OUTPUT33.sdat"

list = [s1,s2,s3]
result = processing.runalg('saga:gridssum',list, None)

And this is the processing log: 

        #####   ##   #####    ##
        ###     ###  ##       ###
        ###   # ## ##  #### # ##
        ### ##### ##    # #####
        ##### #   ##  ##### #   ##
        _____________________________________________

        _____________________________________________
        library path:   C:\PROGRA~1\QGIS2~1.18\apps\saga\modules\grid_calculus.dll
        library name:   Grid - Calculus
        tool name   :   Grids Sum
        author      :   O. Conrad (c) 2010
        _____________________________________________

        Parameters

        Grids: No objects
        Files: E:/rcal/OUTPUT11.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation           

        loading: E:/rcal/OUTPUT11.sdat


        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT11)
        Files: E:/rcal/OUTPUT22.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT22.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]






        Parameters


        Grids: 1 object (OUTPUT22)
        Files: E:/rcal/OUTPUT11.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT11.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT11)
        Files: E:/rcal/OUTPUT22.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT22.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT22)
        Files: E:/rcal/OUTPUT22.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT22.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT22)
        Files: E:/rcal/OUTPUT11.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT11.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT11)
        Files: E:/rcal/OUTPUT22.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT22.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT22)
        Files: E:/rcal/OUTPUT11.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT11.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT11)
        Files: E:/rcal/OUTPUT22.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT22.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grids: 1 object (OUTPUT22)
        Files: E:/rcal/OUTPUT22.sdat
        Transformation: yes
        Interpolation: B-Spline Interpolation


        loading: E:/rcal/OUTPUT22.sdat



        Driver: SAGA

        Bands: 1

        Rows: 177

        Columns: 139



        Transformation:

        x' = 381422.717257 + x * 5.000000 + y * 0.000000

        y' = 433062.210367 + x * 0.000000 + y * -5.000000


        loading band [1/1]



        Parameters


        Grid system: 5; 177x 139y; 381425.217257x 432369.710367y
        Grids: 7 objects (OUTPUT33, OUTPUT33, OUTPUT33, OUTPUT33, OUTPUT33, OUTPUT33, OUTPUT33)
        Sum: Sum





        Error: >> WKT: unknown projection [Double_Stereographic]
        Error: >> WKT: unknown projection [Double_Stereographic]

        C:\PROGRA~1\QGIS2~1.18\bin>exit
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1 Answer 1

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4

If we look for the parameters used for the saga:gridssum algorithm:

>>>import processing
>>>processing.alghelp('saga:gridssum')
ALGORITHM: Rasters sum
    GRIDS <ParameterMultipleInput>
    RESULT <OutputRaster>

We can see that the GRIDS parameter has a multiple input requirement.

So instead of entering a list, we could just split the items in the list and enter them:

s1 = "E:/rcal/OUTPUT11.sdat"
s2 = "E:/rcal/OUTPUT22.sdat"
s3 = "E:/rcal/OUTPUT33.sdat"

my_list = [s1,s2,s3]
result = processing.runalg('saga:gridssum', ";".join(my_list), None)

Note: don't use list as a variable name as there is already a built-in method called this :)

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