cpstruct2pairs

Extract valid control point pairs from cpstruct structure

Syntax

[movingPoints,fixedPoints] = cpstruct2pairs(cpstruct_in)

Description

[movingPoints,fixedPoints] = cpstruct2pairs(cpstruct_in) extracts the valid control point pairs from cpstruct_in, returning two arrays movingPoints and fixedPoints.

Examples

Convert cpstruct to Sets of Control Point Pairs

Read an aerial photograph and an orthoregistered image into the workspace.

aerial = imread('westconcordaerial.png');
ortho = imread('westconcordorthophoto.png');

Load some preselected control points for these images.

load westconcordpoints
whos

  Name                Size                Bytes  Class     Attributes

  aerial            394x369x3            436158  uint8               
  fixedPoints         4x2                    64  double              
  movingPoints        4x2                    64  double              
  ortho             366x364              133224  uint8          

Open the Control Point Selection tool, specifying the two images along with the predefined control points.

cpselect(aerial,ortho,movingPoints,fixedPoints);

Create the cpstruct structure. Using the Control Point Selection tool, select Export Points to Workspace from the File menu to save the points to the workspace. On the Export Points to Workspace dialog box, check the Structure with all points check box, and clear Moving points of valid pairs and Fixed points of valid pairs. Click OK. Close the Control Point Selection tool.

Use cpstruct2pairs to extract the moving and fixed points from the cpstruct.

[mPoints,fPoints] = cpstruct2pairs(cpstruct);

Compare the stored set of points with the set of points you exported.

fixedPoints, fpoints

fixedPoints =

  164.5639  113.2890
  353.5325  130.0798
  143.4046  284.8935
  353.5325  311.9810


fpoints =

  164.5639  113.2890
  353.5325  130.0798
  143.4046  284.8935
  353.5325  311.9810       

The two sets of points are identical, which indicates that all points in the stored set of points belong to valid control point pairs.

Input Arguments

cpstruct_in — Preselected control points

structure

Preselected control points, specified as a structure (cpstruct). cpstruct_in contains information about the x- and y-coordinates of all control points in the moving and fixed images, including unpaired and predicted control points. cpstruct2pairs eliminates unmatched and predicted control points, and returns the set of valid control point pairs.

cpstruct_in is a structure produced by the Control Point Selection tool (cpselect) when you choose the Export Points to Workspace option. For more information, see Export Control Points to the Workspace.

Data Types: struct

Output Arguments

movingPoints — Control point pairs from moving image being aligned

m-by-2 numeric array

Control point pairs from image being aligned, returned as an m-by-2 numeric array. The two columns represent the x- and y-coordinates of the control points, respectively, in the intrinsic coordinate system of the image.

Data Types: double

fixedPoints — Control point pairs from reference image

m-by-2 numeric array

Control point pairs from reference image, returned as an m-by-2 numeric array. The two columns represent the x- and y-coordinates of the control points, respectively, in the intrinsic coordinate system of the image.

Data Types: double

Extended Capabilities

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a

R2021b: Support for thread-based environments

cpstruct2pairs now supports thread-based environments.