projtform2d

2-D projective geometric transformation

Since R2022b

Description

A projtform2d object stores information about a 2-D projective geometric transformation and enables forward and inverse transformations.

Creation

You can create a projtform2d object in these ways:

• fitgeotform2d — Estimate a geometric transformation that maps pairs of control points between two images.

• The projtform2d function described here.

Syntax

tform = projtform2d

tform = projtform2d(A)

tform = projtform2d(tformIn)

Description

tform = projtform2d creates a projtform2d object that performs an identity transformation.

tform = projtform2d(A) creates a projtform2d object and sets the property A as the specified 2-D projective transformation matrix.

tform = projtform2d(tformIn) creates a projtform2d object from another geometric transformation object, tformIn, that represents a valid 2-D projective geometric transformation.

Input Arguments

tformIn — Projective 2-D geometric transformation

affinetform2d object | rigidtform2d object | simtform2d object | transltform2d object | projtform2d object

Projective 2-D geometric transformation, specified as an affinetform2d object, rigidtform2d object, simtform2d object, transltform2d object, or projtform2d object.

Properties

A — Forward 2-D projective transformation

3-by-3 identity matrix (default) | 3-by-3 numeric matrix

Forward 2-D projective transformation, specified as a 3-by-3 numeric matrix. The default value of A is the identity matrix.

The matrix A transforms the point (u, v) in the input coordinate space to the point (x, y) in the output coordinate space using the convention:

$$\left[\begin{array}{c}{x}^{\prime }\\ y^{\prime }\\ k\end{array}\right]={\rm A}\times \left[\begin{array}{c}u\\ v\\ 1\end{array}\right]$$

where x = xʹ / k and y = yʹ / k.

Data Types: double | single

Dimensionality — Dimensionality of geometric transformation

2 (default)

This property is read-only.

Dimensionality of the geometric transformation for both input and output points, specified as 2.

Data Types: double

Object Functions

invert	Invert geometric transformation
outputLimits	Find output spatial limits given input spatial limits
transformPointsForward	Apply forward geometric transformation
transformPointsInverse	Apply inverse geometric transformation

Examples

Create 2-D Projective Transformation

Define a 3-by-3 geometric transformation matrix. This matrix specifies a projective transformation consisting of rotation and tilt.

theta = 30;
A = [cosd(theta) -sind(theta) 0; ...
     sind(theta)  cosd(theta) 0; ...
     0.001        0.001       1];

Create a projtform2d object from the transformation matrix.

tform = projtform2d(A)

tform = 
  projtform2d with properties:

    Dimensionality: 2

                 A: [0.8660   -0.5000         0
                     0.5000    0.8660         0
                     0.0010    0.0010    1.0000]

Examine the value of the A property.

tform.A

ans = 3×3

    0.8660   -0.5000         0
    0.5000    0.8660         0
    0.0010    0.0010    1.0000

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• projtform2d supports the generation of C code (requires MATLAB^® Coder™). For more information, see Code Generation for Image Processing.

• When generating code, you can only specify singular objects. Arrays of objects are not supported.

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 in R2022b

R2022b: Recommended over projective2d

Starting in R2022b, most Image Processing Toolbox™ functions create and perform geometric transformations using the premultiply convention. The projtform2d object stores information about 2-D projective geometric transformations in a format consistent with the premultiply convention.

The projective2d object is not recommended because it uses the postmultiply convention. Although there are no plans to remove the projective2d object at this time, you can streamline your geometric transformation workflows by switching to the projtform2d object. For more information, see Migrate Geometric Transformations to Premultiply Convention.