TfGaussian
サマリー
Defines a Gaussian transformation function which is determined from the midpoint and spread 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
ディスカッション
The tool that uses the TfGaussian object is Rescale by Function.
The equation for the Gaussian transformation function is:
\(\mu(x) = e^{\large -f1 \space * \space {(x - f2)}^2 }\)
The inputs to the equation are \(f1\), the spread, and \(f2\), the midpoint.
The function values range from 0 to 1, which are then transformed to the evaluation scale.
The spread determines how rapidly the transformation function values decrease from the midpoint. If the midpoint is within the lower and upper thresholds, then the spread determines how rapidly the function values decrease from the toScale to the fromScale. The larger the spread, the steeper the function will be around the midpoint. Said another way, as the spread gets smaller, the transformation function approaches the midpoint more slowly.
The selection of an appropriate spread value is a subjective process that is dependent on the range of the input values. The default value of 0.1 is a good starting point. Typically, the values vary within the ranges of 0.01 to 1 or 0.001 to 1, respectively. A default spread is calculated to fit the function to the minimum and maximum of the input dataset.
The Gaussian function is useful when the highest preference is near a specific value.
The Gaussian function is similar to the Near function, except the Near function has a narrower spread and therefore is steeper around the midpoint.
構文
TfGaussian({midpoint}, {spread}, {lowerThreshold}, {valueBelowThreshold}, {upperThreshold}, {valueAboveThreshold})
| 名前 | 説明 | データ タイプ |
|---|---|---|
|
midpoint (オプション) |
The user-defined value that defines the highest point of the Gaussian transformation function curve. If the midpoint value is between the lower and upper threshold, input cell locations with the corresponding value will receive the The default value is None. |
Double |
|
spread (オプション) |
Defines the spread of the Gaussian function that controls the steepness of the decay of the function from the midpoint. The spread generally ranges from 0.01 to 1; the larger the value results in a steeper decay from the midpoint. The default value is None. |
Double |
|
lowerThreshold (オプション) |
Defines the starting value at which to begin applying the specified transformation function. The input value corresponding to the The The default value is None. |
Double |
|
valueBelowThreshold (オプション) |
A user-specified value to assign output cell locations with input values below the The value for The default value is None. |
Variant |
|
upperThreshold (オプション) |
Defines the ending value at which to stop applying the specified transformation function. The input value corresponding to the The The default value is None. |
Double |
|
valueAboveThreshold (オプション) |
A user-specified value to assign output cell locations with input values above the The value for The default value is None. |
Variant |
プロパティ
| 名前 | 説明 | データ タイプ |
|---|---|---|
|
midpoint (読み取り/書き込み) |
The value of the |
Double |
|
spread (読み取り/書き込み) |
The value of the |
Double |
|
lowerThreshold (読み取り/書き込み) |
The value of the |
Double |
|
valueBelowThreshold (読み取り/書き込み) |
The value that will be assigned to the output cells whose input values are below the |
Variant |
|
upperThreshold (読み取り/書き込み) |
The value of the |
Double |
|
valueAboveThreshold (読み取り/書き込み) |
The value that will be assigned to the output cells whose input values are above the |
Variant |
コードのサンプル
Demonstrates how to create a TfGaussian 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("solar", TfGaussian(180, 0.0004, "#", "#", "#", "#"), 1, 10)
outRescale.save("c:/sapyexamples/rescaletfga1")
Demonstrates how to transform the input data with the RescaleByFunction tool using the TfGaussian class.
# Name: TfGaussian_Ex_02.py
# Description: Rescales input raster data using a Gaussian function and
# transforms the function values onto a specified evaluation scale.
# 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
inRaster = "solar"
# Create the TfGaussian object
midpoint = 180
spread = 0.0004
lowerthresh = "#"
valbelowthresh = "#"
upperthresh = "#"
valabovethresh = "#"
myTfFunction = TfGaussian(midpoint, spread, lowerthresh, valbelowthresh, upperthresh, valabovethresh)
# Set evaluation scale
fromscale = 1
toscale = 10
# Run RescaleByFunction
outRescale = RescaleByFunction(inRaster, myTfFunction, fromscale, toscale)
# Save the output
outRescale.save("c:/sapyexamples/rescaletfga2")