# simtform3d

3-D similarity geometric transformation

Since R2022b

## Description

A simtform3d object stores information about a 3-D similarity geometric transformation and enables forward and inverse transformations.

## Creation

### Description

tform = simtform3d creates a simtform3d object that performs an identity transformation.

tform = simtform3d(scale,r,translation) creates a simtform3d object that performs a similarity transformation based on the specified scale factor scale, rotation matrix r, and amounts of translation in the x-, y-, and z-directions translation. The scale, r, and translation arguments set the Scale, R, and Translation properties, respectively.

example

tform = simtform3d(Scale,eulerAngles,Translation) creates a simtform3d object that performs a similarity transformation based on Euler angles and the specified value of the Scale and Translation properties.

tform = simtform3d(A) creates a simtform3d object and sets the property A to the specified 3-D similarity transformation matrix.

tform = simtform3d(tformIn) creates a simtform3d object from another geometric transformation object, tformIn, that represents a valid 3-D similarity geometric transformation.

### Input Arguments

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Euler angles in x,y,z order in degrees, specified as a 3-element numeric vector of the form [rx ry rz]. The Euler angles set the R property as a product of three rotation matrices (Rx, Ry, and Rz) according to:

Rx = [1 0 0; 0 cosd(rx) -sind(rx); 0 sind(rx) cosd(rx)];
Ry = [cosd(ry) 0 sind(ry); 0 1 0; -sind(ry) 0 cosd(ry)];
Rz = [cosd(rz) -sind(rz) 0; sind(rz) cosd(rz) 0; 0 0 1];
R = Rz*Ry*Rx;

Data Types: double | single

Similarity 3-D geometric transformation, specified as an affinetform3d object, rigidtform3d object, simtform3d object, or transltform3d object.

## Properties

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Forward 3-D similarity transformation, specified as a 4-by-4 numeric matrix. The default of A is the identity matrix.

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

$\left[\begin{array}{c}x\\ y\\ z\\ 1\end{array}\right]=Α×\left[\begin{array}{c}u\\ v\\ w\\ 1\end{array}\right]$

For a similarity transformation, A has the form:

$Α=\left[\begin{array}{cccc}s\ast \text{R}\left(1,1\right)& s\ast \text{R}\left(1,2\right)& s\ast \text{R}\left(1,3\right)& {t}_{x}\\ s\ast \text{R}\left(2,1\right)& s\ast \text{R}\left(2,2\right)& s\ast \text{R}\left(2,3\right)& {t}_{y}\\ s\ast \text{R}\left(3,1\right)& s\ast \text{R}\left(3,2\right)& s\ast \text{R}\left(3,3\right)& {t}_{z}\\ 0& 0& 0& 1\end{array}\right]$

where s is the scale factor and corresponds to the Scale property. R(i,j) are the elements of the rotation matrix specified by the corresponding (i,j) indices of the R property. tx, ty, and tz are the amount of translation in the x-, y-, and z-directions, respectively, and correspond to the elements of the Translation property.

Data Types: double | single

Scale factor, specified as a nonzero number. The scale factor corresponds to the value s in the similarity transformation matrix defined by property A.

Data Types: double | single

Rotation matrix, specified as a 3-by-3 numeric matrix. The rotation matrix performs rotation about the z-axis first, then the y-axis, and then the x-axis.

Amount of translation, specified as a 3-element numeric vector of the form [tx ty tz].

Data Types: double | single

Dimensionality of the geometric transformation for both input and output points, specified as 3.

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

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Specify the scale factor and the amount of translation. The transformation in this example does not perform rotation, so set the Euler angles to [0 0 0].

scaleFactor = 1.5;
eulerAngles = [0 0 0];
translation = [10 20.5 15];

Create a simtform3d object that performs the scaling and translation.

tform = simtform3d(scaleFactor,eulerAngles,translation)
tform =
simtform3d with properties:

Dimensionality: 3
Scale: 1.5000
Translation: [10 20.5000 15]
R: [3x3 double]
A: [4x4 double]

Examine the value of the A property.

tform.A
ans = 4×4

1.5000         0         0   10.0000
0    1.5000         0   20.5000
0         0    1.5000   15.0000
0         0         0    1.0000

## Version History

Introduced in R2022b