Available with Spatial Analyst license.
Summary
Defines a Logistic Decay transformation function which is determined from the minimum, maximum, and y intercept percent shape–controlling parameters as well as the lower and upper threshold that identify the range within which to apply the function.
Learn more about how the parameters affect this transformation function
Discussion
The tool that uses the TfLogisticDecay object is Rescale by Function.
The function values range from 0 to 100, which are then transformed to the evaluation scale.
If the minimum parameter is set greater than the lowerThreshold, or the maximum parameter is set less than the upperThreshold, the function curve will decrease at a faster rate. If the minimum parameter is set less than the lowerThreshold, or the maximum parameter is set greater than the upperThreshold, the function curve will decrease at a slower rate.
Syntax
TfLogisticDecay ({minimum}, {maximum}, {yInterceptPercent}, {lowerThreshold}, {valueBelowThreshold}, {upperThreshold}, {valueAboveThreshold})| Parameter | Explanation | Data Type |
minimum |
The starting point for the LogisticDecay transformation function. The minimum must be less than the maximum. (The default value is None) | Double |
maximum | The ending point for the LogisticDecay transformation function. The minimum must be less than the maximum. (The default value is None) | Double |
yInterceptPercent | Determines the value range in the decreasing portion of the logistic decay curve. The greater the yInterceptPercent, the smaller the input value range will be in the decay section of the curve; however, the preference for the values will decrease at a faster rate. A larger yInterceptPercent results in a more pronounced logistic decay curve. The yInterceptPercent must be between 50 and 100. (The default value is 99.0) | Double |
lowerThreshold | Defines the starting value at which to begin applying the specified transformation function. The input value corresponding to the lowerThreshold is assigned to the fromScale evaluation scale value on the output raster. Input values below the lowerThreshold are assigned to the valueBelowThreshold and are not considered in the function value range. The lowerThreshold must be less than the upperThreshold. (The default value is None) | Double |
valueBelowThreshold | A user-specified value to assign output cell locations with input values below the lowerThreshold. The value for valueBelowThreshold can be float, integer, or NoData. In the tool dialog box, no quotation marks are used around NoData; however, quotation marks are required around "NoData" when scripting. (The default value is None) | Variant |
upperThreshold | Defines the ending value at which to stop applying the specified transformation function. The input value corresponding to the upperThreshold is assigned to the toScale evaluation scale value on the output raster. Input values above the upperThreshold are assigned to the valueAboveThreshold and are not considered in the function value range. The lowerThreshold must be less than the upperThreshold. (The default value is None) | Double |
valueAboveThreshold | A user-specified value to assign output cell locations with input values above the upperThreshold. The value for valueAboveThreshold can be float, integer, or NoData. In the tool dialog box, no quotation marks are used around NoData; however, quotation marks are required around "NoData" when scripting. (The default value is None) | Variant |
Properties
| Property | Explanation | Data Type |
| minimum (Read and Write) | The value of the minimum of the transformation function which defines the starting point for the function. | Double |
| maximum (Read and Write) | The value of the maximum of the transformation function which defines the ending point for the function. | Double |
| yInterceptPercent (Read and Write) | The value of the yInterceptPercent for the transformation function which determines the value range that will be in the decreasing portion of the logistic decay curve. | Double |
| lowerThreshold (Read and Write) |
The value of the lowerThreshold for the transformation function which defines the starting value at which to begin applying the specified transformation function. | Double |
| valueBelowThreshold (Read and Write) |
The value that will be assigned to the output cells whose input values are below the lowerThreshold. | Variant |
| upperThreshold (Read and Write) |
The value of the upperThreshold for the transformation function which defines the ending value at which to stop applying the specified function. | Double |
| valueAboveThreshold (Read and Write) | The value that will be assigned to the output cells whose input values are above the upperThreshold. | Variant |
Code sample
Demonstrates how to create a TfLogisticDecay class and use it in the RescaleByFunction tool within the Python window.
import arcpy
from arcpy.sa import *
from arcpy import env
env.workspace = "c:/sapyexamples/data"
outRescale = RescaleByFunction("elevation", TfLogisticDecay(421, 4450, 75, "#", "#", "#", "#"), 1, 10)
outRescale.save("c:/sapyexamples/rescaletfld1")Demonstrates how to transform the input data with the RescaleByFunction tool using the TfLogisticDecay class.
# Name: TfLogisticDecay_Ex_02.py
# Description: Rescales input raster data using a LogisticDecay function and
# transforms the function values onto a specified evaluation scale.
# Requirements: Spatial Analyst Extension
# Author: esri
# 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 = "elevation"
# Create the TfLogisticDecay object
minimum = 421
maximum = 4450
yintercept = 75
lowerthresh = "#"
valbelowthresh = "#"
upperthresh = "#"
valabovethresh = "#"
myTfFunction = TfLogisticDecay(minimum, maximum, yintercept, lowerthresh, valbelowthresh, upperthresh, valabovethresh)
# Set evaluation scale
fromscale = 1
toscale = 10
# Execute RescaleByFunction
outRescale = RescaleByFunction(inRaster, myTfFunction, fromscale, toscale)
# Save the output
outRescale.save("c:/sapyexamples/rescaletfld2")