NbrAnnulus

Summary

Defines an annulus neighborhood which is created by specifying an inner and outer circles' radii in either map units or number of cells.

Illustration

NbrAnnulus neighborhood example for the FocalStatistics function

NbrAnnulus neighborhood example for the BlockStatitistcs function

Discussion

Tools that use neighborhood annulus object: Block Statistics, Focal Statistics, Point Statistics, and Point Density.

The annulus shape is comprised of two circles, one inside the other to make a donut shape. Cells with centers that fall outside the radius of the smaller circle but inside the radius of the larger circle will be included in processing the neighborhood; therefore, the area that falls between the two circles constitutes the annulus neighborhood.

When the annulus object is used and the innerRadius or the outerRadius are not specified, then default values are provided.

The innerRadius must be less than or equal to the outerRadius.

The radius is identified in cells or map units, measured perpendicular to the x- or y-axis. When the radii is specified in map units, they are converted to radii in cell units. The resulting radii in cell units produces an area that most closely represents the area calculated by using the original radii in map units. Any cell center encompassed by the annulus will be included in the processing of the neighborhood.

Syntax

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

Parameter	Explanation	Data Type
innerRadius	The inner radius of an annulus neighborhood. (The default value is 1)	Double
outerRadius	The outer radius of an annulus neighborhood. (The default value is 3)	Double
units	Defines the units of the neighborhood. CELL —The unit of measurement is in cells. MAP —The units are in map coordinates. (The default value is CELL)	String

Properties

Property	Explanation	Data Type
innerRadius (Read and Write)	The inner radius of the annulus neighborhood.	Double
outerRadius (Read and Write)	The outer radius of the annulus neighborhood.	Double
units (Read and Write)	Defines the units of the neighborhood.	String

Code Sample

NbrAnnulus example 1 (Python window)

Demonstrates how to create a NbrAnnulus class and use it in the BlockStatistics tool within the Python window.

import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outNbrA = BlockStatistics("block", NbrAnnulus(1, 2, "CELL"))
outNbrA.save("C:/sapyexamples/output/blstatnbra2")

NbrAnnulus example 2 (stand-alone script)

Implements the BlockStatistics tool using the NbrAnnulus class.

# Name: NbrAnnulus_Ex_02.py
# Description: Uses the NbrAnnulus object to execute BlockStatistics tool.
# Requirements: Spatial Analyst Extension

# 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 = "block"

# Create the Neighborhood Object
innerRadius = 1
outerRadius = 3
myNbrAnnulus = NbrAnnulus(innerRadius, outerRadius, "MAP")

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

# Execute BlockStatistics
outBlkStats =  BlockStatistics(inRaster, myNbrAnnulus, "MINIMUM", "DATA")

# Save the output 
outBlkStats.save("C:/sapyexamples/output/blstat_Ann3")