# matrix geometry transformation

Transformation of geometric objects. 2 M2.1 - Transformation Geometry 1.1 The Euclidean Plane E2 Consider the Euclidean plane (or two-dimensional space) E2 as studied in high school geometry. Up Next. In mathematics, a geometric transformation is any bijection of a set to itself (or to another such set) with some salient geometrical underpinning. how to multiply transformation matrix & vector (hover over each cell) x' y' 1. new vector (hover over the dots) behold the beast! Let $T$ be a linear transformation from $\mathbb{R}^2$ to $\mathbb{R}^2.$ If the matrix of $T$ is of the form $$\begin{bmatrix} \cos \theta & -\sin \theta \\ \sin \theta & \cos \theta \end{bmatrix}$$ then $T$ is a (counterclockwise) rotation transformation through an angle $\theta.$, Proof. If we want to dilate a figure we simply multiply each x- and y-coordinate with the scale factor we want to dilate with. We do not use singular affine transformations in this course. To do so let $w=\begin{bmatrix}w_1\\ w_2\end{bmatrix}$ and $x=\begin{bmatrix}x_1\ x_2\end{bmatrix}.$ Then we find \begin{align*} \operatorname{proj}_L(x) & = \frac{1}{\left|\left| w\right|\right|^2} \left((x_1 w_1+x_2 w_2)\begin{bmatrix} w_1 \\ w_2\end{bmatrix} \right) \\ & = \frac{1}{\left|\left| w\right|\right| ^2} \left((x_1 w_1\begin{bmatrix} w_1 \\ w_2\end{bmatrix}+x_2 w_2 \begin{bmatrix}w_1 \\ w_2\end{bmatrix} \right) \\ & = \frac{1}{\left|\left| w\right|\right|^2} \left(\begin{bmatrix}x_1 w_1^2 \\ x_1w_1 w_2\end{bmatrix} + \begin{bmatrix} x_2w_1w_2 \\ x_2w_2^2\end{bmatrix} \right) \\ & = \frac{1}{\left|\left|w\right|\right|^2} \begin{bmatrix} x_1 w_1^2+x_2w_1w_2 \\ x_1w_1 w_2+x_2w_2^2\end{bmatrix} = \frac{1}{\left|\left|w\right|\right|^2} \begin{bmatrix} w_1^2 & w_1 w_2 \\ w_1 w_2 & w_2^2 \end{bmatrix} \begin{bmatrix} x_1 \\ x_2\end{bmatrix} \end{align*} as desired. Visual representation of transformation from matrix. To see which matrix you need for a given coordinate transformation, all you need to do is look at the way the base vectors change. We give several examples of linear transformations on the real plane that are commonly used in plane geometry. All rights reserved. The transformation matrices are as follows: Mathematics was the elegant language the universe was written in! $$3\cdot \begin{bmatrix} x_{1} &x_{2} &x_{3} &x_{4} \\ y_{1}&y_{2} &y_{3} &y_{4} \end{bmatrix}$$. A vector could be represented by an ordered pair (x,y) but it could also be represented by a column matrix: $$\begin{bmatrix} x\\ y \end{bmatrix}$$ Polygons could also be represented in matrix form, we simply place all of the coordinates of the vertices into one matrix. Find the matrix $A$ of the orthogonal projection onto the line $L$ spanned by $w = \begin{bmatrix} 4 \\ 3 \end{bmatrix}$ and project the vector $u=\begin{bmatrix} 1\\ 5\end{bmatrix}$ onto the line $L$ spanned by $w.$. The transformation matrix usually has a special name such as dilation, contraction, orthogonal projection, reflection, or rotation. Projective transformation enables the plane of the image to tilt. We can use matrices to translate our figure, if we want to translate the figure x+3 and y+2 we simply add 3 to each x-coordinate and 2 to each y-coordinate. Reflection about the x-axis A key feature of such matrix models is that space (and time) emerges from degrees of freedom of matrices. Matrix Transformations. Example. The transformation rotates 45 degrees counterclockwise and has a scaling factor of $\sqrt{2}.$. This is a rotation combined with a scaling. Mathplanet is licensed by Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 Internationell-licens. in Mathematics and has enjoyed teaching precalculus, calculus, linear algebra, and number theory at both the junior college and university levels for over 20 years. When we want to create a reflection image we multiply the vertex matrix of our figure with what is called a reflection matrix. List Geometry - Scaling Geometry - Rotation Geometry - Translation (Addition) Linear Transformations that keep the origin fixed are linear including: Geometry - Rotation, Geometry - … \end{equation} We obtain \begin{equation} \label{ref3} \operatorname{ref}_L(x)=2 \operatorname{proj}_L(x)-x. When A is an invertible matrix there is a matrix A −1 that represents a transformation that "undoes" A since its composition with A is the identity matrix. The coordinate transformation itself consists of using the old coordinates in … In the general linear group , similarity is therefore the same as conjugacy , and similar matrices are also called conjugate ; however in a given subgroup H of the general linear group, the notion of conjugacy may be more restrictive than similarity, since it requires that P be chosen to lie in H . Example. Vocabulary words: transformation / function, domain, codomain, range, identity transformation, matrix transformation. Proof. To shorten this process, we have to use 3×3 transformation matrix instead of 2×2 transformation matrix. \end{align*} The important conclusion is that every linear transformation is associated with a matrix and vice versa. Matrix Transformations. Theorem. Example. Translate the coordinates, 2. Dave will teach you what you need to know, Systems of Linear Equations (and System Equivalency) [Video], Invariant Subspaces and Generalized Eigenvectors, Diagonalization of a Matrix (with Examples), Eigenvalues and Eigenvectors (Find and Use Them), The Determinant of a Matrix (Theory and Examples), Gram-Schmidt Process and QR Factorization, Orthogonal Matrix and Orthogonal Projection Matrix, Coordinates (Vectors and Similar Matrices), Gaussian Elimination and Row-Echelon Form, Linear Transformation (and Characterization), Linear Transformation Matrix and Invertibility, Matrices and Vectors (and their Linear Combinations), Orthonormal Bases and Orthogonal Projections, Solving Linear Equations (Examples and Theory), Choose your video style (lightboard, screencast, or markerboard). A transformation A ↦ P −1 AP is called a similarity transformation or conjugation of the matrix A. Solution. We want to create a reflection of the vector in the x-axis. Visual representation of transformation from matrix. Matrices, Geometric Transformations Moving the blue points on the left will change the transformation matrix. Matrix from visual representation of transformation. The converse of the Pythagorean theorem and special triangles, The surface area and the volume of pyramids, prisms, cylinders and cones, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 Internationell-licens. If a vector $x=\begin{bmatrix} x_1\\ x_2\end{bmatrix}$ is rotated through an angle of $\pi/2$, then a vector $y=\begin{bmatrix} -x_2\\ x_1\end{bmatrix}$ is obtained, via $x\cdot y =0.$ More generally, if we rotate (counterclockwise) a given $x$ through an angle $\theta$ we determine, \begin{align} T(x) & =(\cos \theta) x+(\sin\theta) y =(\cos \theta)\begin{bmatrix}x_1\\ x_2\end{bmatrix} + (\sin \theta)\begin{bmatrix} -x_2\\ x_1\end{bmatrix} \\ &=\begin{bmatrix}(\cos \theta)x_1-(\sin\theta))x_2 \ (\sin \theta)x_1-(\cos\theta))x_2\end{bmatrix} \\ & =\begin{bmatrix} \cos \theta & -\sin \theta \\ \sin \theta & \cos \theta \end{bmatrix} \begin{bmatrix} x_1 \\ x_2\end{bmatrix} =\begin{bmatrix} \cos \theta & -\sin \theta \\ \sin \theta & \cos \theta \end{bmatrix} x \end{align}, Example. To find the image of a point, we multiply the transformation matrix by a column vector that represents the point's coordinate.. Note that the matrix form of an affine transformation is a 4-by-4 matrix with the fourth row 0, 0, 0 and 1. Column major format – convention to hold the space elements (points, vectors) as algebraic column vectors. Theorem. Practice: Matrices as transformations. as needed. \end{align*}, Example. Reflection transformation matrix is the matrix which can be used to make reflection transformation of a figure. A geometric transformation can be represented by a matrix.. If we want to create our vertex matrix we plug each ordered pair into each column of a 4 column matrix:\begin{bmatrix} x_{1} &x_{2} &x_{3} &x_{4} \\ y_{1}&y_{2} &y_{3} &y_{4} \end{bmatrix}= \begin{bmatrix} 1 &-1 & -1 & 1\\ 1 & 1 & -1 & -1 \end{bmatrix}$$. You can move this quadrilateral around to see the effect of the transformation. This allows the multiplication with a transformation matrix from the left. The transformation has a matrix of the form$$ \begin{bmatrix} 2u_1^2-1 & 2 u_1 u_2 \\ 2u_1 u_2 & 2u_2^2-1 \end{bmatrix} $$where u_1=\sqrt{2}/2 and u_2=-\sqrt{2}/2 since 2u_1^2-1=0, 2u_2^2-1=0, and 2u_1 u_2=-1. Since || u ||=1 and u lies on the line y=x, then matrix$$ \begin{bmatrix} 0 & -1 \\ -1 & 0 \end{bmatrix} $$represents the linear transformation which is a reflection through the line y=x.. This is called a vertex matrix. Theorem. Then, apply a global transformation to an image by calling imwarp with the geometric transformation object. Example. We can apply these linear transformations using matrix multiplication by using the matrices \begin{bmatrix} 1 & 0 \\ 2 & 1 \end{bmatrix} and \begin{bmatrix} 1 & 1/2 \\ 0 & 1 \end{bmatrix}.$$ \text{Vertical Shear:} \qquad T\begin{bmatrix} 2 \\ 3 \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 2 & 1 \end{bmatrix} \begin{bmatrix} 2 \\ 3 \end{bmatrix} = \begin{bmatrix} 2 \\ 7 \end{bmatrix}  \text{Horizontal Shear:} \qquad T\begin{bmatrix} 2 \\ 3 \end{bmatrix} = \begin{bmatrix} 1 & 1/2 \\ 0 & 1 \end{bmatrix} \begin{bmatrix} 2 \\ 3 \end{bmatrix} =\begin{bmatrix} 7/2 \\ 3 \end{bmatrix} $$. Given the vector \begin{bmatrix} 2 \\ 3 \end{bmatrix} in \mathbb{R}^2 show geometrically a vertical shear of 2 and a horizontal shear of \frac{1}{2}., Solution. For example, we can write$$ T(x)=\begin{bmatrix} 7 & 0 \\ 0 & 7 \end{bmatrix} x. The transformation you define is then applied to the quadrilateral on the right hand side. Matrix Representation of Geometric Transformations You can use a geometric transformation matrix to perform a global transformation of an image. Yeeeeeah. THE advantage of using transformation matrices is that cumulative transformations can be described by simply multiplying the matrices that describe each individual transformation.. To represent affine transformations with matrices, homogeneous coordinates are used. Solution. Suppose line $L$ is spanned by $w.$ We can decompose any vector $x$ as $x^{||}+x^\perp$ as diagrammed: Notice $x^\perp$ is the perpendicular component so \begin{equation}\label{perpeq} w \cdot x^\perp =0 \qquad \text{or equivalently} \qquad w \cdot (x -x^{||}) =0. Solution. Let $T$ be a linear transformation from $\mathbb{R}^2$ to $\mathbb{R}^2.$ If the matrix of $T$ is of the form $$\begin{bmatrix} k & 0 \\ 0 & k \end{bmatrix}$$ then $T$ is a scaling transformation. Matrix models are expected to give nonperturbative formulation of superstring theory [1– 3]. Theorem. By \cref{rotmatrix}, the matrix of this transformation is $$A= \begin{bmatrix} \sqrt{3}/2 & -1/2 \\ 1/2 & \sqrt{3}/2 \end{bmatrix} .$$ We will use matrix multiplication to perform the transformation, \begin{align} T\begin{bmatrix}4\ 2\end{bmatrix} & = \begin{bmatrix} \frac{\sqrt{3}}{2} & \frac{-1}{2} \\ \frac{1}{2} & \frac{\sqrt{3}}{2} \end{bmatrix} \begin{bmatrix} 4\\ 2\end{bmatrix} =\cos 30^\circ \begin{bmatrix}4\\ 2\end{bmatrix}+\sin 30^\circ \begin{bmatrix}4\\ 2\end{bmatrix} \\ & =\begin{bmatrix}2\left(\sqrt{3}+1\right)\\ \sqrt{3}+1\end{bmatrix}.\end{align}. Transformation Matrices: Dilation and Contraction For a matrix transformation, we translate these questions into the language of matrices. For each [x,y] point that makes up the shape we do this matrix multiplication: When the transformation matrix [a,b,c,d] is the Identity Matrix(the matrix equivalent of "1") the [x,y] values are not changed: Changing the "b" value leads to a "shear" transformation (try it above): And this one will do a diagonal "flip" about the x=y line (try it also): What more can you discover? Example. Each matrix in the matrix product is a basic geometric transformation matrix which corresponds to a basic geometric transformation. Rotate the translated coordinates, and then 3. This is because different authors/programs, use different conventions. Let $T$ be a linear transformation from $\mathbb{R}^2$ to $\mathbb{R}^2.$ If the matrix of $T$ is of the form $$\frac{1}{w_1^2+w_2^2} \begin{bmatrix} w_1^2 & w_1 w_2 \ w_1 w_2 & w_2^2 \end{bmatrix}$$ then $T$ is an orthogonal projection transformation onto the line $L$ spanned by any nonzero vector $w = \begin{bmatrix} w_1 \\ w_2 \end{bmatrix}$ parallel to $L.$. Next lesson. Theorem. The answer is yes since the matrix of the linear transformation is $$\begin{bmatrix} 7 & 0 \\ 0 & 7 \end{bmatrix}$$ which by definition is a scaling. If $k>1$ then the scaling is called a dilation, and is called a contraction when $k<1.$. • If transformation of vertices are known, transformation of linear combination of vertices can be achieved • p and q are points or vectors in (n+1)x1 homogeneous coordinates – For 2D, 3x1 homogeneous coordinates – For 3D, 4x1 homogeneous coordinates • L is a (n+1)x(n+1) square matrix – For 2D, 3x3 matrix – For 3D, 4x4 matrix The information is in fact the same but the order or the sign of the matrix coefficients may be different. Matrices are classified by the number of rows and the number of columns that they have; a matrix A with m rows and n columns is an m ×n (said 'm by n') matrix, and this is called the order of A. The dilation, contraction, orthogonal projection, reflection, rotation, and vertical and horizontal shears are detailed. Matrix from visual representation of transformation. The determinant of a 2x2 matrix. You may be surprised to find that the information we give on this page is different from what you find in other books or on the internet. Matrix Representation of a Rotation. Then \begin{equation}\label{ref1} \operatorname{ref}_L(x)=x^{||}-x^\perp \end{equation} and \begin{equation}\label{ref2} \operatorname{proj}_L(x)=x^{||}. If we want to counterclockwise rotate a figure 90° we multiply the vertex matrix with, $$\begin{bmatrix} 0 & -1\\ 1 & 0 \end{bmatrix}$$, If we want to counterclockwise rotate a figure 180° we multiply the vertex matrix with, $$\begin{bmatrix} -1 & 0\\ 0& -1 \end{bmatrix}$$, If we want to counterclockwise rotate a figure 270°, or clockwise rotate a figure 90°, we multiply the vertex matrix with, $$\begin{bmatrix} 0& 1\\ -1& 0 \end{bmatrix}$$, Rotate the vector A 90° counter clockwise  and draw both vectors in the coordinate plane, $$\underset{A}{\rightarrow}=\begin{bmatrix} -1 & 2\\ -1 & 3 \end{bmatrix}$$. Interpret the linear transformation $$T(x)= \begin{bmatrix} 1& 1 \\ -1 & 1 \end{bmatrix} x$$ geometrically. Copyright © 2020 Dave4Math LLC. Note : It is customary to assign diﬀerent meanings to the terms set and space. If we wanted to plot this, and that is what I'll do. A vector could be represented by an ordered pair (x,y) but it could also be represented by a column matrix: Polygons could also be represented in matrix form, we simply place all of the coordinates of the vertices into one matrix. Moreover, if the inverse of an affine transformation exists, this affine transformation is referred to as non-singular; otherwise, it is singular. In this section we learn to understand matrices geometrically as functions, or transformations. \end{equation} For simplicity assume $L$ is a any line that passes through the origin and let $u$ be a unit vector $u = \begin{bmatrix} u_1 \ u_2 \end{bmatrix}$ lying on $L.$ In the special case of a unit vector $u$ it follows that $\operatorname{proj}_L(x)=(u\cdot x)u.$ Then \begin{align*} \operatorname{ref}_L(x)& =2 \operatorname{proj}_L(x)-x =2(u\cdot x)u-x \\ & = 2(u_1x_1+u_2x_2)\begin{bmatrix} u_1 \\ u_2 \end{bmatrix}-\begin{bmatrix} x_1 \\ x_2 \end{bmatrix} \\ & =2u_1 x_1 \begin{bmatrix} u_1 \\ u_2 \end{bmatrix}+2u_2x_2 \begin{bmatrix} u_1 \\ u_2 \end{bmatrix}-\begin{bmatrix} x_1 \\ x_2 \end{bmatrix} \\ & = \begin{bmatrix} 2u_1^2x_1+2u_1 u_2x_2-x_1 \\ 2u_1u_2x_1+2u_2^2 u_2x_2-x_2 \end{bmatrix} \\& = \begin{bmatrix} 2u_1^2-1 & 2u_1 u_2\\ 2u_1 u_2 & 2u_2^2-1 \end{bmatrix} \begin{bmatrix}x_1\\ x_2\end{bmatrix}. $$We can reflect the vector \begin{bmatrix} 1 \\ 5 \end{bmatrix} about the line L using matrix multiplication$$ T \begin{bmatrix} 1 \\ 5 \end{bmatrix} = \frac{1}{25} \begin{bmatrix} 7 & 24 \\ 24 & -7 \end{bmatrix} \begin{bmatrix} 1 \\ 5 \end{bmatrix} =\begin{bmatrix}127/25\\ -11/25\end{bmatrix}$$as desired. Find the matrix A of a reflection through the line through the origin spanned by w = \begin{bmatrix} 4 \\ 3 \end{bmatrix} and use it to reflect  \begin{bmatrix} 1 \\ 5 \end{bmatrix} about the line L.. Practice: Matrices as transformations. matrices. Try to follow the logic of this lesson without paying too much attention to what other documents might say, and read the next chapter which will explain exactly how different conventions change the way we prese… Transformation Matrices.$$\overrightarrow{A}=\begin{bmatrix} -1 & 3\\ 2 & -2 \end{bmatrix}$$, In order to create our reflection we must multiply it with correct reflection matrix, Hence the vertex matrix of our reflection is,$$\\ \begin{bmatrix} -1 & 0\\ 0 & 1 \end{bmatrix} \cdot \begin{bmatrix} -1 & 3\\ 2 & -2 \end{bmatrix}=\\ \\\\\begin{bmatrix} (1\cdot -1)+(0\cdot2) & (1\cdot3)+(0\cdot-2)\\ (0\cdot-1)+(-1\cdot2) & (0\cdot3)+(-1\cdot-2) \end{bmatrix}= \begin{bmatrix} -1 & 3\\ -2 & 2 \end{bmatrix}$$, If we want to rotate a figure we operate similar to when we create a reflection. Base vectors e 1 and e 2 turn into u and v, respectively, and these vectors are the contents of the matrix. To convert a 2×2 matrix to 3×3 matrix, we h… Scale the rotated coordinates to complete the composite transformation. Unlike affine transformations, there are no restrictions on the last column of the transformation matrix. Let T be a linear transformation from \mathbb{R}^2 to \mathbb{R}^2. If the matrix of T is of the form$$ \begin{bmatrix} 1 & 0 \\ k & 1 \end{bmatrix} \qquad \text{or} \qquad \begin{bmatrix} 1 & k \\ 0 & 1 \end{bmatrix}, $$where k is any constant, then T defines a vertical shear or horizontal shear transformation, respectively. We give several examples of linear transformations on the real plane that are commonly used in plane geometry. Parallel lines can converge towards a vanishing point, creating the appearance of depth. Matrix Representation of a "Stretch" Matrix Representation of Transformations. and M.S.$$ from $\mathbb{R}^2$ to $\mathbb{R}^2$ a scaling? Dave4Math Â» Linear Algebra Â» Transformation Matrix (Plane Geometry). Next lesson. In some practical applications, inversion can be computed using general inversion algorithms or by performing inverse operations (that have obvious geometric interpretation, like rotating in opposite direction) and then composing them in reverse order. Matrix Representation of a Shear. The determinant of a 2x2 matrix. The transformation is a 3-by-3 matrix. \end{equation} To project $x$ onto the line $L$ we notice \begin{equation}\label{projfac} x^{||}=k w \end{equation} for some scalar $k.$ By substitution solving for $k$ we obtain \begin{equation}\label{facdef} k=\frac{w \cdot x}{w \cdot w}. \end{equation} We define the orthogonal projection of a vector $x$ onto a given line $L$ as \begin{equation}\label{projdef} \operatorname{proj}_L(x) =\frac{w \cdot x}{\left|\left| w \right|\right|}^2 w. \end{equation} We would like to have the form of a matrix. Articles Related Matrix A geometric transformation is represented by a transformation matrix. The most common reflection matrices are: $$\begin{bmatrix} 1 & 0\\ 0 & -1 \end{bmatrix}$$, $$\begin{bmatrix} -1 & 0\\ 0 & 1 \end{bmatrix}$$, $$\begin{bmatrix} -1 & 0\\ 0 & -1 \end{bmatrix}$$, $$\begin{bmatrix} 0 & 1\\ 1 & 0 \end{bmatrix}$$. Intuitively, a space is … Transformation matrix – a matrix that holds a specific transformation of the geometry. This is called a vertex matrix. Video transcript. There is really nothing complicated about matrices and why some people fear them is mostly because they don't really fully comprehend what they represent and how they work. THE advantage of using transformation matrices is that cumulative transformations can be described by simply multiplying the matrices that describe each individual transformation. Towards the end, I combine them to produce some interesting linear transformation. To perform a sequence of transformation such as translation followed by rotation and scaling, we need to follow a sequential process − 1. Let $u=\begin{bmatrix}4/5 \\ 3/5\end{bmatrix}.$ We notice $u$ is a unit vector, since $\left|\left| u \right|\right| =1.$ Then the matrix we seek is  A=\begin{bmatrix} 7/25 & 24/25 \\ 24/25 & -7/25 \end{bmatrix}. The transformation matrix usually has a special name such as dilation, contraction, orthogonal projection, reflection, or rotation. The above transformations (rotation, reflection, scaling, and shearing) can be represented by matrices. They play an instrumental part in the graphics pipeline and you will see them used regularly in the code of 3D applications.In the previous chapter we mentioned that it was possible to translate or rotate points by using linear operators. The Image of a Matrix Transformation.