Focal Statistics (Spatial Analyst)

Summary

Calculates for each input cell location a statistic of the values within a specified neighborhood around it.

Learn more about how Focal Statistics works

Illustration

OutRas = FocalStatistics(InRas1, NbrRectangle(3,3,MAP), "SUM", "")

Usage

• If the input raster is of floating point type, only the Mean, Maximum, Minimum, Range, STD, and Sum statistics are available; the Majority, Minority, Median and Variety statistics are not permitted. If the input raster is of integer type, all the statistics types are available.

• The values on the output raster depend on the operation.

• When a circular, annulus-shaped, or wedge-shaped neighborhood is specified, some of the outer diagonal cells may not be considered in the calculations since the center of the cell must be encompassed within the neighborhood.

• The Irregular and Weight Neighborhood types require a Kernel file be specified. Kernel files should have a ".txt" file extension.

  See the Irregular and Weight sections of How Focal Statistics works for information on creating and using kernel files.

• Only for the statistics types of Mean, Standard Deviation, or Sum can the Neighborhood type can be set to Weight.

• Input NoData cells may receive a value in the output if the Ignore NoData in calculations option is checked, provided at least one cell within the neighborhood has a valid value.

Syntax

FocalStatistics (in_raster, {neighborhood}, {statistics_type}, {ignore_nodata})

Parameter	Explanation	Data Type
in_raster	The raster to perform the focal statistics calculations on.	Raster Layer
neighborhood (Optional)	The Neighborhood class dictates the shape of the area around each cell used to calculate the statistic. The different types of neighborhood available are: NbrAnnulus, NbrCircle, NbrRectangle, NbrWedge, NbrIrregular, and NbrWeight. The following are the forms of the neighborhoods: NbrAnnulus({innerRadius}, {outerRadius}, {CELL | MAP}) NbrCircle({radius}, {CELL | MAP} NbrRectangle({width}, {height}, {CELL | MAP}) NbrWedge({radius}, {start_angle}, {end_angle}, {CELL | MAP}) NbrIrregular(kernel_file) NbrWeight(kernel_file) The {CELL | MAP} parameter defines the distance units as either being Cell units or Map units. The default neighborhood is a square NbrRectangle with a width and height of 3 cells.	Neighborhood
statistics_type (Optional)	The statistic type to be calculated. MEAN — Calculates the mean (average value) of the cells in the neighborhood. MAJORITY — Calculates the majority (value that occurs most often) of the cells in the neighborhood. MAXIMUM — Calculates the maximum (largest value) of the cells in the neighborhood. MEDIAN — Calculates the median of the cells in the neighborhood. MINIMUM — Calculates the minimum (smallest value) of the cells in the neighborhood. MINORITY — Calculates the minority (value that occurs least often) of the cells in the neighborhood. RANGE — Calculates the range (difference between largest and smallest value) of the cells in the neighborhood. STD — Calculates the standard deviation of the cells in the neighborhood. SUM — Calculates the sum (total of all values) of the cells in the neighborhood. VARIETY — Calculates the variety (the number of unique values) of the cells in the neighborhood. The default statistic type is MEAN.	String
ignore_nodata (Optional)	Denotes whether NoData values are ignored by the statistic calculation. DATA — Specifies that if a NoData value exists within a neighborhood, the NoData value will be ignored. Only cells within the neighborhood that have data values will be used in determining the output value. This is the default. NODATA —Specifies that if any cell in a neighborhood has a value of NoData, the output for the processing cell will be NoData. With this option, the presence of a NoData value implies that there is insufficient information to determine the statistic value for the neighborhood.	Boolean

Return Value

Name	Explanation	Data Type
out_raster	The output focal statistics raster.	Raster

Code Sample

FocalStatistics example 1 (Python window)

This example calculates the least-frequently occuring value in a ring-shaped neighborhood around each cell in the input raster.

import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outFocalStat = FocalStatistics("elevation", NbrAnnulus(5, 10, "CELL"), 
                               "MINORITY", "NODATA")
outFocalStat.save("C:/sapyexamples/output/focalstat01")

FocalStatistics example 2 (stand-alone script)

This example determines the least frequently occurring value in a 10-by-10 neighborhood around each cell in the input raster.

# Name: FocalStatistics_Ex_02.py
# Description: Calculates a statistic on a raster over a specified
#    neighborhood.
# 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
inRaster = "elevation"
neighborhood = NbrRectangle(10, 10, "CELL")

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

# Execute FocalStatistics
outFocalStatistics = FocalStatistics(inRaster, neighborhood, "MINORITY",
                                     "")

# Save the output 
outFocalStatistics.save("C:/sapyexamples/output/focalstatout")

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