VfSec (arcpy.sa)

Summary

Defines the relationship between the vertical cost factor and the vertical relative moving angle through a secant function.

Illustration

VfSec vertical factor for the PathDistance functions.

Discussion

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

The vertical factor (VF) object defines the relationship between the vertical cost factor and the vertical relative moving angle (VRMA).

VF defines the vertical difficulty encountered in moving from one cell to the next.

VRMA identifies the slope angle between the FROM or processing cell and the TO cell.

The VF is determined by the secant function of the VRMA.

Syntax

VfSec ({lowCutAngle}, {highCutAngle}, {secPower})

Parameter	Explanation	Data Type
lowCutAngle	The VRMA degree defining the lower threshold, below which (less than) the VFs are set to infinity. (The default value is -90.0)	Double
highCutAngle	The VRMA degree defining the upper threshold, beyond which (larger than) the VFs are set to infinity. (The default value is 90.0)	Double
secPower	The power to which the values in the secant VRMA function will be raised. The VF is determined by: VF = sec(VRMA)power (The default value is 1.0)	Double

Properties

Property	Explanation	Data Type
lowCutAngle (Read and Write)	The VRMA degree defining the lower threshold, below which (less than) the VFs are set to infinity.	Double
highCutAngle (Read and Write)	The VRMA degree defining the upper threshold, beyond which (larger than) the VFs are set to infinity.	Double
secPower (Read and Write)	The power to which the values in the secant VRMA function will be raised. The VF is determined by: VF = sec(VRMA)power	Double

Code Sample

VfSec example 1 (Python window)

Demonstrates how to create a VfSec 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"
myVerticalFactor = VfSec(-90, 90, 1)
outPathDist = PathDistance("source.shp", "costraster", "","", "", "",
                           myVerticalFactor)
outPathDist.save("C:/sapyexamples/output/pathdistvfs")

VfSec example 2 (stand-alone script)

Performs a PathDistance analysis using the VfSec class.

# Name: VfSec_Ex_02.py
# Description: Uses the VfSec 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 = "source.shp"
inCostRaster = "costraster"

# Create the VfSec Object
lowCutAngle = -90
highCutAngle = 90
secPower = 1
myVerticalFactor = VfSec(lowCutAngle, highCutAngle, secPower)

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

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

# Save the output 
outPathDist.save("C:/sapyexamples/output/pathdistvfs2")