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Create Accuracy Assessment Points

Available with Spatial Analyst license.

Available with Image Analyst license.

Summary

Creates randomly sampled points for post-classification accuracy assessment.

A common practice is to randomly select hundreds of points and label their classification types by referencing reliable sources, such as field work or human interpretation of high-resolution imagery. The reference points are then compared with the classification results at the same locations.

Usage

  • This tool creates a set of random points and assigns a class to them based on reference data.

  • This tool can also assign a class to the set of points using a previously classified image or a feature class.

  • After running this tool, you can edit the table if you want to manually assign a class to some or all of the points.

Syntax

CreateAccuracyAssessmentPoints (in_class_data, out_points, {target_field}, {num_random_points}, {sampling})
ParameterExplanationData Type
in_class_data

The input classification image or other thematic GIS reference data. The input can be a raster or feature class.

Typical data is a classification image of a single band, integer data type.

If using polygons as input, only use those that are not used as training samples. They can also be GIS land-cover data in shapefile or feature class format.

Raster Layer; Mosaic Layer; Feature Layer
out_points

The output point shapefile or feature class that contains the random points to be used for accuracy assessment.

Feature Class
target_field
(Optional)

Specifies whether your input data is a classified image or ground truth data.

  • CLASSIFIEDThe input is a classified image. This is the default.
  • GROUND_TRUTHThe input is reference data.
String
num_random_points
(Optional)

The total number of random points that will be generated.

The actual number may exceed but never fall below this number, depending on sampling strategy and number of classes. The default number of randomly generated points is 500.

Long
sampling
(Optional)

Specify a sampling scheme to use.

  • STRATIFIED_RANDOMCreate points that are randomly distributed within each class, where each class has a number of points proportional to its relative area. This is the default
  • EQUALIZED_STRATIFIED_RANDOMCreate points that are randomly distributed within each class, where each class has the same number of points.
  • RANDOMCreate points that are randomly distributed throughout the image.
String

Code sample

CreateAccuracyAssessment example 1 (stand-alone script)

This example creates random points for accuracy assessment.

import arcpy
from arcpy.ia import *

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

CreateAccuracyAssessmentPoints("c:\\test\\cls.tif", "c:\\test\\apnt1.shp", 
                               "COMPUTED", "1500", "RANDOM")

Licensing information

  • Basic: Requires Image Analyst or Spatial Analyst
  • Standard: Requires Image Analyst or Spatial Analyst
  • Advanced: Requires Image Analyst or Spatial Analyst

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