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images.geotrans.PiecewiseLinearTransformation2D class

Package: images.geotrans

2-D piecewise linear geometric transformation

Description

A PiecewiseLinearTransformation2D object encapsulates a 2-D piecewise linear geometric transformation.

You can create a PiecewiseLinearTransformation2D object using the following methods:

  • fitgeotrans — Returns a PiecewiseLinearTransformation2D object that maps control point pairs using a piecewise linear transformation

  • The PiecewiseLinearTransformation2D class constructor

Construction

tform = images.geotrans.PiecewiseLinearTransformation2D(movingPoints,fixedPoints) creates a PiecewiseLinearTransformation2D object given m-by-2 matrices movingPoints and fixedPoints, which define matched control points in the moving and fixed images, respectively. The piecewise linear transformation creates a mapping by breaking up the plane into regions and using a different affine transformation to map control points in each region.

Input Arguments

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x- and y-coordinates of control points in the moving image, specified as an m-by-2 matrix.

Data Types: double | single

x- and y-coordinates of control points in the fixed image, specified as an m-by-2 matrix.

Data Types: double | single

Properties

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Describes the dimensionality of the geometric transformation for both input and output points.

Methods

images.geotrans.PiecewiseLinearTransformation2D.outputLimitsFind output limits of geometric transformation
images.geotrans.PiecewiseLinearTransformation2D.transformPointsInverseApply inverse geometric transformation

Copy Semantics

Value. To learn how value classes affect copy operations, see Copying Objects (MATLAB) in the MATLAB® documentation.

Examples

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Fit a piecewise linear transformation to a set of fixed and moving control points that are actually related by a single global affine2d transformation across the domain.

Create a 2D affine transformation.

theta = 10;
tformAffine = affine2d([cosd(theta) -sind(theta) 0; sind(theta) cosd(theta) 0; 0 0 1])
tformAffine = 

  affine2d with properties:

                 T: [3x3 double]
    Dimensionality: 2

Arbitrarily choose 6 pairs of control points.

fixedPoints = [10 20; 10 5; 2 3; 0 5; -5 3; -10 -20];

Apply forward geometric transformation to map fixed points to obtain effect of fixed and moving points that are related by some geometric transformation.

movingPoints = transformPointsForward(tformAffine,fixedPoints)
movingPoints =

   13.3210   17.9597
   10.7163    3.1876
    2.4906    2.6071
    0.8682    4.9240
   -4.4031    3.8227
  -13.3210  -17.9597

Estimate piecewise linear transformation that maps movingPoints to fixedPoints.

tformPiecewiseLinear = images.geotrans.PiecewiseLinearTransformation2D(movingPoints,fixedPoints)
tformPiecewiseLinear = 

  PiecewiseLinearTransformation2D with properties:

    Dimensionality: 2

Verify the fit of our PiecewiseLinearTransformation2D object at the control points.

movingPointsComputed = transformPointsInverse(tformPiecewiseLinear,fixedPoints);
 
errorInFit = hypot(movingPointsComputed(:,1)-movingPoints(:,1),...
                   movingPointsComputed(:,2)-movingPoints(:,2))
errorInFit =

   1.0e-15 *

         0
         0
    0.4441
         0
         0
         0
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