- (Subtraction)
Summary
Subtracts the value of the second input raster from the value of the first input raster on a cell-by-cell basis.
Illustration
 |
OutRas = Raster("InRas1") - Raster("InRas2") |
Discussion
The - (Minus) operator is an overloaded operator since it exists in both Spatial Analyst and Python. To distinguish an input is a raster as opposed to a scalar variable the input raster is cast using the Raster class: Raster("inRas"). If both input are scalars, the Python - operator will be used working on scalars. If one or both of the input are rasters (identified by casting with the Raster class), the Spatial Analyst - is used and will work on each cell within the rasters.
The order of input is relevant for this operation.
If both input values are integers, the output values will be integers; otherwise, the output will be floating-point values.
Another way to perform the subtraction operator is a -= b which is an alternative way to write a = a - b.
Syntax
| Operand | Explanation | Data Type |
in_raster_or_constant1 |
The input from which to subtract the values in the second input. If the first input is a raster and the second is a scalar, an output raster is created with each input raster value being subtracted by the scalar value. | Raster Layer | Constant |
in_raster_or_constant2 |
The input values to subtract from the values in the first input. If the first input is a scalar and the second is a raster, an output raster is created with each input raster value being subtracted from the scalar value. | Raster Layer | Constant |
Return Value
| Name | Explanation | Data Type |
| out_raster |
The output raster object. The cell values are the result of subtracting the second input from the first. | Raster |
Code Sample
This sample subtracts the values of the second input raster from the first.
import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outMinus = Raster("degs") - Raster("negs")
outMinus.save("C:/sapyexamples/output/outminus")
This sample subtracts the values of the second input raster from the first.
# Name: Op_Minus_Ex_02.py
# Description: Subtracts the value of the second input raster from the
# value of the first input raster on a cell-by-cell basis
# Requirements: Spatial Analyst Extension
# Author: ESRI
# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *
# Set environment settings
env.workspace = "C:/sapyexamples/data"
# Set local variables
inRaster1 = Raster("degs")
inRaster2 = Raster("negs")
# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")
# Execute Minus
outMinus = inRaster1 - inRaster2
# Save the output
outMinus.save("C:/sapyexamples/output/outminus.tif")