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projective2d class

2-D projective geometric transformation

Description

A projective2d object encapsulates a 2-D projective geometric transformation.

You can create a projective2d object using the following methods:

  • fitgeotrans — Returns a projective2d object that maps control point pairs

  • The projective2d class constructors

Construction

tform = projective2d() creates a projective2d object with default property settings that correspond to the identity transformation.

tform = projective2d(A) creates a projective2d object given an input 3-by-3 matrix A that specifies a valid projective transformation.

Input Arguments

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Forward 2-D projective transformation, specified as a 3-by-3 numeric matrix. A has the form:

 A = [a b c;
      d e f;
      g h i]

Data Types: double | single

Properties

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Forward 2-D projective transformation, specified as a 3-by-3 numeric matrix.

The matrix T uses the convention:

[x y 1] = [u v 1] * T

where T has the form:

[a b c;...
 d e f;...
 g h i];

The default of T is the identity transformation.

Data Types: double | single

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

Methods

invertInvert geometric transformation
outputLimitsFind output spatial limits given input spatial limits
transformPointsForwardApply forward geometric transformation
transformPointsInverseApply inverse 2-D geometric transformation to points

Copy Semantics

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

Examples

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This example shows how to apply rotation and tilt to an image, using a projective2d geometric transformation object created directly from a transformation matrix.

Read a grayscale image into the workspace.

I = imread('pout.tif');

Create a geometric transformation object. This example combines rotation and tilt into a transformation matrix, tm. Use this transformation matrix to construct a projective2d geometric transformation object, tform.

theta = 10;
tm = [cosd(theta) -sind(theta) 0.001; ...
    sind(theta) cosd(theta) 0.01; ...
    0 0 1];
tform = projective2d(tm);

Apply the transformation using imwarp. View the transformed image.

outputImage = imwarp(I,tform);
figure
imshow(outputImage);

Create a projective2d object that defines the transformation.

theta = 10;
tform = projective2d([cosd(theta) -sind(theta) 0.001; sind(theta) cosd(theta) 0.01; 0 0 1]);
tform = 

  projective2d with properties:

                 T: [3x3 double]
    Dimensionality: 2

Apply forward geometric transformation to an input point.

[X,Y] = transformPointsForward(tform,5,10)
X =

    6.0276


Y =

    8.1265

Apply inverse geometric transformation to output point from previous step to recover the point we started with.

[U,V] = transformPointsInverse(tform,X,Y)
U =

    5.0000


V =

    10

Extended Capabilities

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