Focal Statistics (Image Analyst)

Available with Spatial Analyst license.

Available with Image Analyst license.

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

Input and output values from the Focal Statistics tool for a rectangle neighborhood with the Sum statistic set
OutRas = FocalStatistics(InRas1, NbrRectangle(3,3,"CELL"), "SUM", "DATA")

Usage

  • There are several neighborhood shapes and statistics types to choose from. The available statistics depend on the type of the input raster.

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

  • The irregular and weight Neighborhood types require that 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 about creating and using kernel files.

  • For integer input rasters, the valid choices for Statistics type are: majority, maximum, mean, median, minimum, minority, percentile, range, standard deviation, sum, and variety. For float input rasters, the valid statistics are: maximum, mean, median, minimum, percentile, range, standard deviation, and sum. Majority, minority, and variety are not available.

  • If the input raster is integer, the output raster will be integer for the following statistics: majority, maximum, minimum, minority, range, sum, and variety. The output will be float for: mean, median, percentile, and standard deviation.

    If the input raster is of float type, the output will be float for all of the available statistic types.

  • For the Median setting of the Statistics type parameter, if the neighborhood has an odd number of cells, the values will be ranked and the middle value will be reported as the median. If the neighborhood has an even number of cells, the values will be ranked and the middle two values will be averaged.

  • For the Majority setting of the Statistics type parameter, if one cell value occurs most frequently in the neighborhood (a single value with the highest frequency of occurrence), that value will be returned for the processing cell. If two or more cell values have the highest frequency of occurrence (a tie among cell values), no single majority value is identified, and the output for that processing cell will be NoData. For the Minority setting, ties among the least frequently occurring values in a neighborhood will also be assigned NoData.

  • The Neighborhood parameter can be set to Weight only for the Mean, Standard deviation, and Sum statistic types.

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

Parameters

LabelExplanationData Type
Input raster

The raster for which the focal statistics for each input cell will be calculated.

Raster Layer
Neighborhood
(Optional)

The cells surrounding a processing cell that will be used in the statistic calculation. There are several predefined neighborhood types to choose from, or a custom kernel can be defined.

Once the neighborhood type is selected, other parameters can be set to fully define the shape, size, and units of measure. The default neighborhood is a square rectangle with a width and height of three cells.

The following are the forms of the available neighborhood types:

  • Annulus, Inner radius, Outer radius, Units type

    A torus (donut-shaped) neighborhood defined by an inner radius and an outer radius. The default annulus is an inner radius of one cell and an outer radius of three cells.

  • Circle, Radius, Units type

    A circular neighborhood with the given radius. The default radius is three cells.

  • Rectangle, Height, Width, Units type

    A rectangular neighborhood defined by height and width. The default is a square with a height and width of three cells.

  • Wedge, Radius, Start angle, End angle, Units type

    A wedge-shaped neighborhood defined by a radius, the start angle, and the end angle. The wedge extends counterclockwise from the starting angle to the ending angle. Angles are specified in degrees, with 0 or 360 representing east. Negative angles can be used. The default wedge is from 0 to 90 degrees, with a radius of three cells.

  • Irregular, Kernel file

    A custom neighborhood with specifications set by the identified kernel text file.

  • Weight, Kernel file

    A custom neighborhood with specifications set by the identified kernel text file, which can apply weights to the members of the neighborhood.

For the annulus, circle, rectangle and wedge neighborhood types, the distance units for the parameters can be specified in Cell units or Map units. Cell units is the default.

For kernel neighborhoods, the first line in the kernel file defines the width and height of the neighborhood in numbers of cells. The subsequent lines indicate how the input value that corresponds to that location in the kernel will be processed. A value of 0 in the kernel file for either the irregular or the weight neighborhood type indicates the corresponding location will not be included in the calculation. For the irregular neighborhood, a value of 1 in the kernel file indicates that the corresponding input cell will be included in the operation. For the weight neighborhood, the value at each position indicates what the corresponding input cell value is to be multiplied by. Positive, negative, and decimal values can be used.

Neighborhood
Statistics type
(Optional)

Specifies the statistic type to be calculated.

The default statistic type is Mean.

If the input raster is integer, all the statistics types will be available. If the input raster is floating point, only the Mean, Maximum, Median, Minimum, Percentile, Range, Standard deviation, and Sum statistic types will be available.

  • MeanThe mean (average value) of the cells in the neighborhood will be calculated.
  • MajorityThe majority (value that occurs most often) of the cells in the neighborhood will be identified.
  • MaximumThe maximum (largest value) of the cells in the neighborhood will be identified.
  • MedianThe median of the cells in the neighborhood will be calculated. Median is equivalent to the 50th percentile.
  • MinimumThe minimum (smallest value) of the cells in the neighborhood will be identified.
  • MinorityThe minority (value that occurs least often) of the cells in the neighborhood will be identified.
  • PercentileA percentile of the cells in the neighborhood will be calculated. The 90th percentile is calculated by default. You can specify other values (from 0 to 100) using the Percentile value parameter.
  • RangeThe range (difference between largest and smallest value) of the cells in the neighborhood will be calculated.
  • Standard deviationThe standard deviation of the cells in the neighborhood will be calculated.
  • SumThe sum of the cells in the neighborhood will be calculated.
  • VarietyThe variety (the number of unique values) of the cells in the neighborhood will be calculated.
String
Ignore NoData in calculations
(Optional)

Specifies whether NoData values will be ignored by the statistic calculation.

  • Checked—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. If the processing cell itself is NoData, the processing cell may receive a value in the output raster, provided at least one cell within the neighborhood has a valid value. This is the default.
  • Unchecked—If any cell in a neighborhood has a value of NoData, including the processing cell, the output for the processing cell will be NoData. The presence of a NoData value implies that there is insufficient information to determine the statistic value for the neighborhood.
Boolean
Percentile value
(Optional)

The percentile value that will be calculated. The default is 90, for the 90th percentile.

The values can range from 0 to 100. The 0th percentile is essentially equivalent to the minimum statistic, and the 100th percentile is equivalent to the maximum statistic. A value of 50 will produce essentially the same result as the median statistic.

This option is only supported if the Statistics type parameter is set to Percentile. If any other statistic type is specified, this parameter will be ignored.

Double

Return Value

LabelExplanationData Type
Output raster

The output focal statistics raster.

Raster

FocalStatistics(in_raster, {neighborhood}, {statistics_type}, {ignore_nodata}, {percentile_value})
NameExplanationData Type
in_raster

The raster for which the focal statistics for each input cell will be calculated.

Raster Layer
neighborhood
(Optional)

The cells surrounding a processing cell that will be used in the statistic calculation. There are several predefined neighborhood types to choose from, or a custom kernel can be defined.

Once the neighborhood type is selected, other parameters can be set to fully define the shape, size, and units of measure. The default neighborhood is a square rectangle with a width and height of three cells.

The shape of the neighborhoods are defined by the Neighborhood class. The available neighborhood types are NbrAnnulus, NbrCircle, NbrRectangle, NbrWedge, NbrIrregular, and NbrWeight.

The following are the forms of the available neighborhood types:

  • NbrAnnulus({innerRadius}, {outerRadius}, {units})

    A torus (donut-shaped) neighborhood defined by an inner radius and an outer radius. The default annulus is an inner radius of one cell and an outer radius of three cells.

  • NbrCircle({radius}, {units}

    A circular neighborhood with the given radius. The default radius is three cells.

  • NbrRectangle({width}, {height}, {units})

    A rectangular neighborhood defined by height and width. The default is a square with a height and width of three cells.

  • NbrWedge({radius}, {startAngle}, {endAngle}, {units})

    A wedge-shaped neighborhood defined by a radius, the start angle, and the end angle. The wedge extends counterclockwise from the starting angle to the ending angle. Angles are specified in degrees, with 0 or 360 representing east. Negative angles can be used. The default wedge is from 0 to 90 degrees, with a radius of three cells.

  • NbrIrregular(inKernelFile)

    A custom neighborhood with specifications set by the identified kernel text file.

  • NbrWeight(inKernelFile)

    A custom neighborhood with specifications set by the identified kernel text file, which can apply weights to the members of the neighborhood.

For the NbrAnnulus, Nbrcircle, NbrRectangle and NbrWedge neighborhoods, the distance units for the parameters can be specified in CELL units or MAP units. Cell units is the default.

For kernel neighborhoods, the first line in the kernel file defines the width and height of the neighborhood in numbers of cells. The subsequent lines indicate how the input value that corresponds to that location in the kernel will be processed. A value of 0 in the kernel file for either the irregular or the weight neighborhood type indicates the corresponding location will not be included in the calculation. For the irregular neighborhood, a value of 1 in the kernel file indicates that the corresponding input cell will be included in the operation. For the weight neighborhood, the value at each position indicates what the corresponding input cell value is to be multiplied by. Positive, negative, and decimal values can be used.

Neighborhood
statistics_type
(Optional)

Specifies the statistic type to be calculated.

  • MEANThe mean (average value) of the cells in the neighborhood will be calculated.
  • MAJORITYThe majority (value that occurs most often) of the cells in the neighborhood will be identified.
  • MAXIMUMThe maximum (largest value) of the cells in the neighborhood will be identified.
  • MEDIANThe median of the cells in the neighborhood will be calculated. Median is equivalent to the 50th percentile.
  • MINIMUMThe minimum (smallest value) of the cells in the neighborhood will be identified.
  • MINORITYThe minority (value that occurs least often) of the cells in the neighborhood will be identified.
  • PERCENTILEA percentile of the cells in the neighborhood will be calculated. The 90th percentile is calculated by default. You can specify other values (from 0 to 100) using the percentile_value parameter.
  • RANGEThe range (difference between largest and smallest value) of the cells in the neighborhood will be calculated.
  • STDThe standard deviation of the cells in the neighborhood will be calculated.
  • SUMThe sum of the cells in the neighborhood will be calculated.
  • VARIETYThe variety (the number of unique values) of the cells in the neighborhood will be calculated.

The default statistic type is MEAN.

If the input raster is integer, all the statistics types will be available. If the input raster is floating point, only the MEAN, MAXIMUM, MEDIAN, MINIMUM, PERCENTILE, RANGE, STD, and SUM statistic types will be available.

String
ignore_nodata
(Optional)

Specifies whether NoData values will be ignored by the statistic calculation.

  • DATAIf 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. If the processing cell itself is NoData, the processing cell may receive a value in the output raster, provided at least one cell within the neighborhood has a valid value. This is the default.
  • NODATAIf any cell in a neighborhood has a value of NoData, including the processing cell, the output for the processing cell will be NoData. The presence of a NoData value implies that there is insufficient information to determine the statistic value for the neighborhood.
Boolean
percentile_value
(Optional)

The percentile value that will be calculated. The default is 90, for the 90th percentile.

The values can range from 0 to 100. The 0th percentile is essentially equivalent to the minimum statistic, and the 100th percentile is equivalent to the maximum statistic. A value of 50 will produce essentially the same result as the median statistic.

This option is only supported if the statistics_type parameter is set to PERCENTILE. If any other statistic type is specified, this parameter will be ignored.

Double

Return Value

NameExplanationData Type
out_raster

The output focal statistics raster.

Raster

Code sample

FocalStatistics example 1 (Python window)

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

import arcpy
from arcpy import env
from arcpy.ia import *
env.workspace = "C:/data"
outFocalStat = FocalStatistics("elevation", NbrAnnulus(5, 10, "CELL"), 
                               "MINORITY", "NODATA")
outFocalStat.save("C:/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: Image Analyst Extension

# Import system modules
import arcpy
from arcpy import env
from arcpy.ia import *

# Set environment settings
env.workspace = "C:/data"

# Set local variables
inRaster = "elevation"
neighborhood = NbrRectangle(10, 10, "CELL")

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

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

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

Licensing information

  • Basic: Requires Image Analyst or Spatial Analyst
  • Standard: Requires Image Analyst or Spatial Analyst
  • Advanced: Requires Image Analyst or Spatial Analyst

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