# Take Minimum value of multiple raster using ArcPy

Question asked by india123 on Jul 12, 2018
Latest reply on Jul 17, 2018 by india123

Hi all,

I have monthly raster for different parameters in three different folders. I am trying to take the minimum value of raster from each raster in two different parameters and solve the below equation. For that, I have written a code, but the code is producing an error.

It is giving an error in line no 35.

Sample data attached below

Code:

``def main():    import arcpy    import os    arcpy.env.overwriteOutput = True    # Checkout extension    arcpy.CheckOutExtension("Spatial")    ws_in_APAR = r'E:\APAR'    ws_in_TSCALAR = r'E:\T_SCALAR'    ws_in_WSCALAR = r'E:\W_SCALAR'    ws_out_GPP = r'E:\GPP_1982'    # list "mean" rasters (r001_APAR so on)    arcpy.env.workspace = ws_in_APAR    lst_ras_APAR = arcpy.ListRasters()    print "lst_ras_APAR", lst_ras_APAR    # list "mean" rasters (r001_TSCALAR so on)    arcpy.env.workspace = ws_in_TSCALAR    lst_ras_TSCALAR = arcpy.ListRasters()    print "lst_ras_TSCALAR", lst_ras_TSCALAR    # list "mean" rasters (r001_WSCALAR so on)    arcpy.env.workspace = ws_in_WSCALAR    lst_ras_WSCALAR = arcpy.ListRasters()    print "lst_ras_WSCALAR", lst_ras_WSCALAR    for ras_name in lst_ras_APAR, lst_ras_TSCALAR, lst_ras_WSCALAR   :        ras_APAR = arcpy.Raster(os.path.join(ws_in_APAR, ras_APAR))        ras_TSCALAR = arcpy.Raster(os.path.join(ws_in_TSCALAR, ras_TSCALAR))        ras_WSCALAR = arcpy.Raster(os.path.join(ws_in_WSCALAR, ras_WSCALAR))        # calculate (ras_TSCALAR.minimum wil take the minimum value of perticular raster)        ras_GPP = (ras_APAR * 1.48) * (ras_TSCALAR.minimum * ras_WSCALAR.minimum)        # save raster        ras_num = ras_name[:3]        out_name_GPP = os.path.join(ws_out_GPP, 'r{0}_GPP'.format(ras_num))        ras_GPP.save(out_name_GPP)if __name__ == '__main__':    main()``

Error message:

``Traceback (most recent call last):  File "E:\GPP.py", line 64, in <module>    main()  File "E:\GPP.py", line 47, in main    ras_APAR = arcpy.Raster(os.path.join(ws_in_APAR, ras_APAR))UnboundLocalError: local variable 'ras_APAR' referenced before assignment``