Performing QGIS modeler multiple raster calculations with data from external CSV?

Question

I need to perform multiple calculations on a set of rasters based on values in a CSV metadata file.

I'm using the QGIS graphical modeler and can call a specific field in a CSV with the Table and Table Field inputs.

Since I have multiple rasters, and each raster has a corresponding value in the CSV, how do I call the specific row? (similar to a lookup for instance).

I don't want to add a script if I don't have to for ease of use.

Answer 1

Really old post but I guess a possible solution is to, unfortunately for your case, use a script in your modeler which:

• Retrieves the names all loaded raster layers.
• Iterate through the metadata which contains a column with raster names.
• Matches the loaded raster names with those in the metadata.
• If any matches are found, the raster's corresponding value is extracted.

---

1. You can create a script from:

   Processing Toolbox > Scripts > Tools > Create new script
   

   Then use something like the following which:

   ##Example=name
   ##Table=table
   ##Field=Field Table
   ##Output_value=output Number
   
   from qgis.core import QgsMapLayer, QgsMapLayerRegistry
   import csv
   
   raster_list = [layer.name() for layer in QgsMapLayerRegistry.instance().mapLayers().values() if layer.type() == QgsMapLayer.RasterLayer]
   with open(Table) as f:
       reader = csv.reader(f)
       for row in reader:
           for raster in raster_list:
               if raster in row[0]:
                   Output_value = row[1]
                   print Output_value
   

---

2. Then add the script into your modeler (I made a simple example with just two inputs):

   

   If I run this model using the script above, it simply prints the output value from the metadata which corresponds to the name of the raster:

   

---

3. Depending on how your model is contructed and possibly tweaking the script, you could perform your multiple raster calculations.