A colleague and I have downloaded QGIS Dufour and are trying to use the Graphical Modeler to carry out a raster subtraction with a DSM and a DTM. This fails using both the Grid Difference and Raster Calculator tools with a message box saying the output file could not be opened.

If the same operation is attempted using the Raster Calculator outside of the Graphical Modeler it works fine and a good result is achieved.

Has anyone got any ideas or a solution?



  • Hi, can you paste the content of the message box. Thank you. – Matthias Kuhn Dec 4 '13 at 17:27
  • 1
    What does the log say from menu Processing > History and log. What type of installation did you use: Standalone / OSGeo4W / Linux / Mac – Jakob Dec 5 '13 at 11:26
  • Another log: C:\Users\MYUSER\.qgis2\processing\processing_qgis.log – Jakob Dec 5 '13 at 11:37
  • Grid system: 1; 1000x 1000y; 0.5x 0.5y Grids: 2 objects (2mresdsm, 2mresdtm)) Grids from different Systems: No objects Result: Result Formula: dsm - dtm Name: Calculation Take Formula: no Use NoData: no error: Error in formula at position 0 [d] sm - dtm function not found error: executing module [Grid Calculator] – MinExMan Dec 5 '13 at 17:31
  • I think I'm making a newbie error. The formula seems to have an error and fails to work which has a knock on effect. Having named the raster inputs dsm and dtm I am entering dsm - dtm into the raster calculator equation box. Is there a syntax issue? – MinExMan Dec 5 '13 at 17:34

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