ArcMap

Update Accuracy Assessment Points

Available with Spatial Analyst license.

Summary

Updates fields in the attribute table to compare ground truth points to the classified image. It can also update the set of points used for accuracy assessment to reflect changes in the classification scheme or in the ground truth data.

Accuracy assessment takes known points and uses them to assess the validity of the classification model.

Usage

  • Update the attribute table of a feature class that represents accuracy assessment points. If you created the feature class using the Create Accuracy Assessment Points tool, there will be a field for GROUND_TRUTH and for CLASSIFIED. This tool can start with either ground truth data and compare it to the classified output, or it can start with the classified output and compare that to ground truth data.

    These two fields are then compared using the Compute Confusion Matrix geoprocessing tool.

  • You can also update the set of points with data from an additional input raster or feature class.

  • You can manually update the GROUND_TRUTH field if you want to change or identify a set of points.

Syntax

UpdateAccuracyAssessmentPoints (in_class_data, in_points, out_points, {target_field})
ParameterExplanationData Type
in_class_data

Input classification image or other thematic GIS data in raster or feature class format.

Typical data is a classification image (single band, integer data type) or the training polygon output from an ArcMap image classification toolbar.

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

Raster Layer | Feature Layer
in_points

The point feature class providing the accuracy assessment points to be updated.

All points from this input will be copied to the updated output feature class, and the target_field will be updated from the input raster or feature class data.

Feature Layer
out_points

The output point feature class which contains the updated random point field for accuracy assessment purposes.

Feature Class
target_field
(Optional)

There are two options: CLASSIFIED and GROUND_TRUTH. If you want to assess the accuracy of a classified image, choose CLASSIFIED. If the input is considered ground truth or reference data, such as a training polygon shapefile or feature class, choose GROUND_TRUTH.

  • CLASSIFIED —Creates a field in the attribute table that shows the corresponding value from the classified image for each point.
  • GROUND_TRUTH —Appends points to an existing set of accuracy assessment points.
String

Code sample

UpdateAccuracyAssessment example 1 (stand-alone script)

This example updates the points used for accuracy assessment.

import arcpy
from arcpy.sa import *

arcpy.gp.UpdateAccuracyAssessmentPoints("aapnt1.shp", "grndtru.tif", "aapnt2.shp", "GROUND_TRUTH")

Environments

Licensing information

  • ArcGIS Desktop Basic: Requires Spatial Analyst
  • ArcGIS Desktop Standard: Requires Spatial Analyst
  • ArcGIS Desktop Advanced: Requires Spatial Analyst

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