Applying QGIS Raster Calculator upon two different Rasters?

Question

I want to Apply some calculations over rasters ,For which using Following Code.

  import time
  from qgis.analysis import QgsRasterCalculator, QgsRasterCalculatorEntry
  rasterpath='inputfile1'
  bohLayer = QgsRasterLayer(rasterpath,"temp")
  QgsMapLayerRegistry.instance().addMapLayer(bohLayer )
  entries = []
  # Define band1
  boh1 = QgsRasterCalculatorEntry()
  boh1.ref = 'boh@1'
  boh1.raster = bohLayer
  boh1.bandNumber = 1
  entries.append( boh1 )


  rasterpath='inputfile2'
  bohLayer1 = QgsRasterLayer(rasterpath,"temp1")
  QgsMapLayerRegistry.instance().addMapLayer(bohLayer1)

  # Define band2
  boh2 = QgsRasterCalculatorEntry()
  boh2.ref = 'boh1@1'
  boh2.raster = bohLayer1
  boh2.bandNumber = 1
  entries.append( boh2 )

  # Process calculation with input extent and resolution
  calc =QgsRasterCalculator('Float(boh1@1-boh@1)/Float(boh1@1+boh@1)','outputfile','GTiff', bohLayer.extent(), bohLayer.width(), bohLayer.height(), entries )
  calc.processCalculation()

But it Gives out 4 as parse Error instead of 0(as success) what is the error in code ??

Answer 1

You need to include a space when using mathematical operators with references to rasters in your formula. So try changing

Float(boh1@1-boh@1)/Float(boh1@1+boh@1)

to

Float(boh1@1 - boh@1)/Float(boh1@1 + boh@1)