# Map Algebra with ImageMath¶

You can open the ImageMath raster calculator under Applications ‣ ImageMath

## Calculate NDVI¶

• Make sure to open the testdatasets for this example

• Specify the input and output parameters according to the screenshot below (you can of course alter the names, but make sure to also adapt them in the script)

• Enter this code in the editor on the right side. You do not need to alter Output Grid and Processing for now.

# select the red band
red = enmap[38]
# select the nir band
nir = enmap[64]
# calculate ndvi
ndvi = (nir-red)/(nir+red)

• Click the run button . The result should be listed in the Data Sources panel.

• Make sure to open the testdatasets for this example

• Select enmap_berlin.bsq under Inputs and name it enmap. Further select landcover_berlin_polygon.shp and name it mask.

• Under Outputs specify output path and file and name it result

• Enter this code in the editor

result = enmap
# set all cells not covered by mask to nodata
result[:, mask[0] == 0] = noDataValue(enmap)
# specify nodata value
setNoDataValue(result, noDataValue(enmap))
# copy metadata to result raster