HfForward (arcpy.sa)

Summary

Defines the relationship between the horizontal cost factor and the horizontal relative moving angle through a forward function. The function establishes that only forward movement is allowed.

Illustration

HfForward horizontal factor for the PathDistance functions.

Discussion

The HfForward object is used in the Spatial Analyst tools Path Distance, Path Distance Allocation, and Path Distance Back Link.

If a horizontal relative moving angle (HRMA) is less than 45 degrees for a section of travel, the horizontal factor (HF) is set to the value associated with the zeroFactor. When the HRMA is larger than or equal to 45 degrees and less than 90 degrees, the HF is set to the sideValue. If the HRMA is equal to or greater than 90 degrees, the HF is set to infinity.

Syntax

HfForward ({zeroFactor}, {sideValue})

Parameter	Explanation	Data Type
zeroFactor	The zeroFactor will be used to position the y-intercept of the forward function. (The default value is 0.5)	Double
sideValue	Identifies the HF value that will be assigned for HRMAs that are equal to or less than 45 degrees and less than 90 degrees. In the diagram above, the sideValue is assigned 1. (The default value is 1.0)	Double

Properties

Property	Explanation	Data Type
zeroFactor (Read and Write)	The zeroFactor will be used to position the y-intercept of the function. The zeroFactor is assigned as the horizontal factor when HRMA is less then the cut angle.	Double
sideValue (Read and Write)	Identifies the HF value that will be assigned for HRMAs that are equal to or less than 45 degrees and less than 90 degrees. In the diagram above the sideValue is assigned 1.	Double

Code Sample

HfForward example 1 (Python window)

Demonstrates how to create an HfForward class and use it in the PathDistance tool within the Python window.

import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
myHorizFactor = HfForward(0.5, 1.0)
outPathDist = PathDistance("sourcepts.shp", "costraster", "", "", myHorizFactor)
outPathDist.save("C:/sapyexamples/output/pathdisthff")

HfForward example 2 (stand-alone script)

Performs a PathDistance analysis using the HfForward class.

# Name: HfForward_Ex_02.py
# Description: Uses the HfForward object to execute the PathDistance 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
inSourceData = "sourcepts.shp"
inCostRaster = "costraster"

# Create the HfForward Object
zeroFactor = 0.5
sideValue = 1.0
myHorizFactor = HfForward(zeroFactor, sideValue)

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

# Execute PathDistance
outPathDist = PathDistance(inSourceData, inCostRaster, "", "", myHorizFactor)

# Save the output 
outPathDist.save("C:/sapyexamples/output/pathdisthff2")