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TfLogisticGrowth

Available with Spatial Analyst license.

Summary

Defines a Logistic Growth 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 TfLogisticGrowth 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 increase 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 increase at a slower rate.

Syntax

TfLogisticGrowth ({minimum}, {maximum}, {yInterceptPercent}, {lowerThreshold}, {valueBelowThreshold}, {upperThreshold}, {valueAboveThreshold})
ParameterExplanationData Type
minimum

The starting point for the LogisticGrowth transformation function.

The minimum must be less than the maximum.

(The default value is None)

Double
maximum

The ending point for the LogisticGrowth transformation function.

The minimum must be less than the maximum.

(The default value is None)

Double
yInterceptPercent

Determines the value range in the increasing portion of the logistic growth curve. The smaller the yInterceptPercent, the smaller the input value range will be in the growth section of the curve; however, the preference for the values will increase at a faster rate. A smaller yInterceptPercent results in a more pronounced logistic growth curve.

The yInterceptPercent must be between 0 and 50.

(The default value is 1.0)

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

PropertyExplanationData 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 increasing portion of the logistic growth 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

Transformation function LogisticGrowth example 1 (Python window)

Demonstrates how to create a TfLogisticGrowth 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("biomass", TfLogisticGrowth(30, 412000, 15, "#", "#", "#", "#"), 1, 10)
outRescale.save("c:/sapyexamples/rescaletflg1")
Transformation function LogisticGrowth example 2 (stand-alone script)

Demonstrates how to transform the input data with the RescaleByFunction tool using the TfLogisticGrowth class.

# Name: TfLogisticGrowth_Ex_02.py
# Description: Rescales input raster data using a LogisticGrowth 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 = "biomass"

# Create the TfLogisticGrowth object
minimum = 30
maximum = 412000
yintercept = 15
lowerthresh = "#"
valbelowthresh = "#"
upperthresh = "#"
valabovethresh = "#"
myTfFunction = TfLogisticGrowth(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/rescaletflg2")

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