ArcGIS Help 10.1 - VfSymLinear (arcpy.sa)

Summary

Defines the relationship between the vertical cost factor and the vertical relative moving angle (VRMA) through a symmetrical linear function in either the negative or positive side of the VRMA, respectively. The two linear functions are symmetrical with respect to the VF (y) axis.

Illustration

VfSymLinear vertical factor for the PathDistance functions.

Discussion

The VfSymLinear 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 VfSymLinear class is composed of two linear functions relative to the VRMAs that are symmetrical to the VF (y) axis. Both lines intercept the y-axis at the VF value associated with the zeroFactor. The slope of the lines is defined as a single slope relative to the positive VRMA using the slope vertical factor argument, which is mirrored to the negative VRMAs.

Syntax

VfSymLinear ({zeroFactor}, {lowCutAngle}, {highCutAngle}, {slope})

Parameter	Explanation	Data Type
zeroFactor	The zeroFactor will be used to position the y-intercept of the symmetric linear function. (The default value is 1.0)	Double
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
slope	Identifies the slope of the straight line in the VRMA-VF coordinate system. Slope is specified as the rise/run. For example, a 30-degree slope is 1/30, specified as 0.03333 (rise/run: 1 VF on the y axis / 30 degrees on the x axis); a 90-degree slope as 0.011111. (The default value is 0.011111)	Double

Properties

Property	Explanation	Data Type
zeroFactor (Read and Write)	The zeroFactor is used to position the y-intercept for the vertical factor class.	Double
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
slope (Read and Write)	Identifies the slope of the straight line in the VRMA-VF coordinate system. Slope is specified as the rise over the run. For example, a 30-degree slope is 1/30, specified as 0.03333 (rise/run: 1 VF on the y axis / 30 degrees on the x axis); a 90-degree slope as 0.011111.	Double

Code Sample

VfSymLinear example 1 (Python window)

Demonstrates how to create a VfSymLinear 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 = VfSymLinear(1.0, -90, 90, -0.01111)
outPathDist = PathDistance("source.shp", "costraster", "", "", "", "",
                           myVerticalFactor)
outPathDist.save("C:/sapyexamples/output/pathdistvfsl")

VfSymLinear example 2 (stand-alone script)

Performs a PathDistance analysis using the VfSymLinear class.

# Name: VfSymLinear_Ex_02.py
# Description: Uses the VfSymLinear 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 VfSymLinear Object
zeroFactor = 1.0
lowCutAngle = -90
highCutAngle = 90
slope = -0.01111
myVerticalFactor = VfSymLinear(zeroFactor, lowCutAngle, highCutAngle, slope)

# 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/pathdistvfsl2")