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I need to create temporary files as intermediate output to be used with processing algorithms. So, I implemented this:

Processing.runalgorithm("grass:v.to.rast.attribute", ........, None)

This line creates the output in C:\Users...\AppData\Local\Temp\AppData\processing\"folder"\output.tif

In this temp directory, three folders are created.

Now, I need to run other algorithm:

Processing.runAlgorithm("saga...", input,....)

The input of this is the output of the last algorithm, I am trying to access that but I can´t.

I try with system.getTempFilenameInTempFolder('output'+'.'+'tif'). But this line only access one of the three folders.

I research in http://docs.qgis.org/2.6/pt_PT/docs/user_manual/processing/console.html, and try the code presented for qgis 2.6 (but didn't work):

##dem=raster
##twi=output
ret_slope = processing.runalg("saga:slopeaspectcurvature", dem, 0, None,
                None, None, None, None)
ret_area = processing.runalg("saga:catchmentarea(mass-fluxmethod)", dem,
                0, False, False, False, False, None, None, None, None, None)
processing.runalg("saga:topographicwetnessindex(twi), ret_slope['SLOPE'],
                ret_area['AREA'], None, 1, 0, twi)

What can I do to access the output?

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  • There's a double-quotation mark missing in the third process saga:topographicwetnessindex(twi). Might not fix the problem though.
    – Joseph
    Jan 7, 2015 at 15:40
  • I don't understand what are you refered to. What is missing? Can you confirm that ret_slope['SLOPE'] and ret_area['AREA'] are the correct way to call the outputs? Because I try also and it doesn't work.
    – Bárbara Duarte
    Jan 7, 2015 at 16:00
  • Welcome to gis.stackexchange! Please reword the title of your thread to contain enough information for future readers who might be looking for the same information
    – underdark ♦
    Jan 7, 2015 at 17:41

2 Answers 2

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I reckon the results of any processing algorithm is a dictionary whose first element is called 'OUTPUT'. This means that calling ret_slope['SLOPE'] should instead be written as ret_slope['OUPUT']

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I am no expert in this field but I tend to find it easier to "name" each algorithm I use such as the following:

outputs_1=processing.runalg("qgis:fieldcalculator", Layer, ............, None)
outputs_2=processing.runalg("qgis:deletecolumn", outputs_1, ..........., Result)

Doing this should allow you to ignore typing in the location of where the temporary files are stored and their filename.

Hope this helps!

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  • I try that option but gives me nothing also.
    – Bárbara Duarte
    Jan 7, 2015 at 10:59
  • If you know exactly where the file is, you can include the file location into your code. Eg, in your second example, replace input with "C:\Users...\AppData\Local\Temp\AppData\processing\"folder"\output.tif". Note the quotes.
    – Joseph
    Jan 7, 2015 at 11:05
  • I know the directory but the folder where the file is created is always different and it is automatically created. It is like this:"C:\Users...\AppData\Local\Temp\AppData\processing\addaf198a04e4c2da465a75d8bc88320\output.tif". If I run again the folder created has another name and so on, and so on,...
    – Bárbara Duarte
    Jan 7, 2015 at 11:15
  • The other alternative I can think of is to save the outputs in a specific directory instead of creating temporary files. Then use that directory in the code, you can always delete the outputs manually or use python. Apologies but hopefully others can provide a definitive answer for you!
    – Joseph
    Jan 7, 2015 at 11:23
  • Thanks anyway. I try that option, I save the files in a directory and I try to remove in the end but gives me error. So, I think the best option is to create temporary files. Thanks anyway.
    – Bárbara Duarte
    Jan 7, 2015 at 11:24

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