MA 108 Lecture Notes - Lecture 3: Rotation Matrix, Main Diagonal, Identity Matrix
31 Jan 2019
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Document Summary
A rotation is an isometry, so rotations preserve size (and shape). While rotation is a quite general concept and the center and angle of rotation can, If a point a is rotated about a center c, then the angle aca" is the angle of rotation. Case 1: 90 degree rotation about the origin. When a point is rotated 90 degrees, the x- coordinate of the image is the opposite of the original y-coordinate, and the y-coordinate of the image is the original x-coordinate. In coordinate notation, (x", y") = ( y, x ). For example, the point ( 3, 5) has the image ( -5, 3), and the point ( -2, -7) has the image ( 7, -2). multiplying the polygon matrix by the rotation matrix [ 0 -1 . The rotation matrix goes in front of the polygon matrix (this is called premultiplying ).
