Create Normal Raster (Spatial Analyst)

Summary

Creates a raster of random values with a normal (gaussian) distribution within the extent and cell size of the analysis window.

Illustration

OutRas = CreateNormalRaster(1, 0 0 4 4)

Note: This output is representative. The actual values will be different each time the tool is executed.

Usage

• The Create Normal Raster tool generates values for every cell in the output raster.

• The output raster from this tool is always floating point.

• The cell values will have up to 7 digits of precision after the decimal point.

• The output values will have a mean of 0.0 and a standard deviation of 1.0. If a different standard deviation is desired, multiply the output raster by that value. If a different mean is desired, add that value to the raster. For example, to create a raster where the values are characterized by a mean of 39 and a standard deviation of 2.5, multiply the results of Create Normal Raster by 2.5, then add 39.

  • In Map Algebra, you could do something like:

    import arcpy
    from arcpy import env
    from arcpy.sa import *
    env.workspace = "C:/data"
    outNorm = CreateNormalRaster(1, Extent(0, 0, 100, 100)) * 2.5 + 39
    outNorm.save("C:/output/norm2")

• The random number generator is automatically seeded with the current value of the system clock (seconds since January 1, 1970). Reseeding the Create Random Raster tool also reseeds Create Normal Raster.

Syntax

CreateNormalRaster ({cell_size}, {extent})

Parameter	Explanation	Data Type
cell_size (Optional)	The cell size for the output raster dataset. This is the value in the environment if specifically set. If not specifically set, it is the shorter of the width or height of the environment extent in the output spatial reference, divided by 250.	Analysis Cell Size
extent (Optional)	The extent for the output raster dataset. The Extent is a Python class. In this tool it is in the form of: Extent(XMin, YMin, XMax, YMax) where XMin and YMin define the lower-left coordinate of the extent, with XMax and YMax defining the upper-right coordinate. The coordinates are specified in the same map units as the in_raster. The extent will be the value in the environment if specifically set. If not specifically set, the default is 0, 0, 250, 250.	Extent

Return Value

Name	Explanation	Data Type
out_raster	The output raster of normally distributed values with a mean of 0.0 and a standard deviation of 1.0.	Raster

Code Sample

CreateNormalRaster example 1 (Python window)

This sample creates an output raster of normally distributed values at the defined cell size and extent.

import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outNormalRaster = CreateNormalRaster(2, Extent(0, 0, 150, 150))
outNormalRaster.save("C:/sapyexamples/output/outnormal")

CreateNormalRaster example 2 (stand-alone script)

This sample creates an output raster of normally distributed values at the defined cell size and extent.

# Name: CreateNormalRaster_Ex_02.py
# Description: Creates a raster of random values from a normal distribution
# 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
cellSize = 2
extent = Extent(0, 0, 150, 150)

# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")

# Execute CreateNormalRaster
outNormalRaster = CreateNormalRaster(cellSize, extent) 

# Save the output 
outNormalRaster.save("C:/sapyexamples/output/outnormraster")

Environments

Cell Size, Current Workspace, Mask, Output Coordinate System, Extent, Scratch Workspace, Snap Raster

Licensing Information

ArcView: Requires Spatial Analyst

ArcEditor: Requires Spatial Analyst

ArcInfo: Requires Spatial Analyst