Jinxiang Chai CSCE441: Computer Graphics 3D Transformations 0

Outline 2D Coordinate transformation Composite transformation 3D transformation Required readings: HB 7-8, 9-1 to 9-9 1

Image space Coordinate Transform: 3D Geometry Pipeline 2 Normalized project space View space World spaceObject space Aspect ratio & resolution Focal length Rotate and translate the camera

Coordinate Transformation: 3D Modeling/Design Coordinate transformation from one reference frame to another 3

Coordinate Transformation: Animation/Robotics How to model 2D movement of animated characters or robots? 4 Click herehere

Coordinate Transformation Coordinate transformation from one reference frame to another 5

Coordinate Transformation Coordinate transformation from one reference frame to another 6 Local reference frame

Coordinate Transformation Coordinate transformation from one reference frame to another 7 Local reference frame Global reference frame

Coordinate Transformation Coordinate transformation from one reference frame to another ? 8 Local reference frame Global reference frame

Review – Vector Operations Dot Product 9

Review – Vector Operations Dot Product: measuring similarity between two vectors 10

Review – Vector Operations Dot Product: measuring similarity between two vectors 11

Review – Vector Operations Dot Product: measuring similarity between two vectors Unit vector: 12

Review – Vector Operations Dot Product: measuring similarity between two vectors 13

Review – Vector Operations Dot Product: measuring similarity between two vectors 14

Review – Vector Operations Cross Product: measuring the area determined by two vectors 15

Review – Vector Operations Cross Product: measuring the area determined by two vectors 16

2D Coordinates 2D Cartesian coordinate system: P: (x,y) 17

2D Coordinate Transformation 2D Cartesian coordinate system: P: (x,y) 18

2D Coordinate Transformation 2D Cartesian coordinate system: P: (x,y) 19

2D Coordinate Transformation Transform object description from to p 20

2D Coordinate Transformation Transform object description from to p 21 Given the coordinates (x’,y’) in i’j’ - how to compute the coordinates (x,y) in ij?

2D Coordinate Transformation Transform object description from to p 22 Given the coordinates (x’,y’) in i’j’ - how to compute the coordinates (x,y) in ij?

2D Coordinate Transformation Transform object description from to p 23 Given the coordinates (x’,y’) in i’j’ - how to compute the coordinates (x,y) in ij?

2D Coordinate Transformation Transform object description from to p 24

2D Coordinate Transformation Transform object description from to p 25

2D Coordinate Transformation Transform object description from to p 26

2D Coordinate Transformation Transform object description from to p 27

2D Coordinate Transformation Transform object description from to p 28

2D Coordinate Transformation Transform object description from to p 29

2D Coordinate Transformation Transform object description from to p 30

2D Coordinate Transformation Transform object description from to p 31

2D Coordinate Transformation Transform object description from to p 32

2D Coordinate Transformation Transform object description from to p 33

2D Coordinate Transformation Transform object description from to p 34

2D Coordinate Transformation Transform object description from to p 35

2D Coordinate Transformation Transform object description from to p 36

2D Coordinate Transformation p 37 What does this column vector mean?

2D Coordinate Transformation Transform object description from to p 38 What does this column vector mean? Vector i’ in the new reference system

2D Coordinate Transformation Transform object description from to p 39 What does this column vector mean?

2D Coordinate Transformation Transform object description from to p 40 What does this column vector mean? Vector j’ in the new reference system

2D Coordinate Transformation Transform object description from to p 41 What does this column vector mean?

2D Coordinate Transformation Transform object description from to p 42 What does this column vector mean? The old origin in the new reference system

2D Coordinate Transformation 2D translation p 43

2D Coordinate Transformation 2D translation p ? ? ? ? 44

2D Coordinate Transformation 2D translation p

2D Coordinate Transformation 2D translation&rotation p ? 46

2D Coordinate Transformation 2D translation&rotation p ? 47

2D Coordinate Transformation 2D translation&rotation p 48

2D Coordinate Transformation 2D translation&rotation p ? 49

2D Coordinate Transformation 2D translation&rotation p 50

2D Coordinate Transformation 2D translation&rotation p ? 51

2D Coordinate Transformation 2D translation&rotation p 52

2D Coordinate Transformation An alternative way to look at the problem P=[x,y] 53 - set up a transformation that superimposes the x’y’ axes onto the xy axis

2D Coordinate Transformation An alternative way to look at the problem P=[x,y] 54 - set up a transformation that superimposes the x’y’ axes onto the xy axis

2D Coordinate Transformation An alternative way to look at the problem P=[x,y] 55 - set up a transformation that superimposes the x’y’ axes onto the xy axis

2D Coordinate Transformation An alternative way to look at the problem This transforms the point from (x,y) to (x’,y’) p 56

2D Coordinate Transformation An alternative way to look at the problem This transforms the point from (x,y) to (x’,y’) How to transform the point from (x’,y’) to (x,y)? p 57

2D Coordinate Transformation An alternative way to look at the problem This transforms the point from (x,y) to (x’,y’) How to transform the point from (x’,y’) to (x,y)? Invert the matrix! p 58

2D Coordinate Transformation An alternative way to look at the problem This transforms the point from (x,y) to (x’,y’) How to transform the point from (x’,y’) to (x,y)? Invert the matrix! p 59

2D Coordinate Transformation An alternative way to look at the problem This transforms the point from (x,y) to (x’,y’) How to transform the point from (x’,y’) to (x,y)? Invert the matrix! p 60

2D Coordinate Transformation An alternative way to look at the problem This transforms the point from (x,y) to (x’,y’) How to transform the point from (x’,y’) to (x,y)? Invert the matrix! p 61

2D Coordinate Transformation An alternative way to look at the problem This transforms the point from (x,y) to (x’,y’) How to transform the point from (x’,y’) to (x,y)? Invert the matrix! p 62

2D Coordinate Transformation Same results! p 63

2D Coordinate Transformation 2D translation&rotation p 64

2D Coordinate Transformation 2D translation&rotation p 65

2D Coordinate Transformation 2D translation&rotation p 66

2D Coordinate Transformation 2D translation&rotation p 67

2D Coordinate Transformation 2D translation&rotation p 68

2D Coordinate Transformation 2D translation&rotation p 69

Composite 2D Transformation How to model 2D movement of characters or robots? 70 Click herehere

Composite 2D Transformation A 2D lamp character 71

Composite 2D Transformation A 2D lamp character – skeleton size 72

Composite 2D Transformation How can we draw the character given the pose ? 73

Articulated Character Local reference frames with a default pose (0,0,0,0,0,0)

Composite 2D Transformation What’s the pose? 75

Composite 2D Transformation What’s the pose? 76

Composite 2D Transformation A 2D lamp character Given,, how to compute the global position of a point A? ? 77

Composite 2D Transformation What’s local coordinate ? ? 78

Composite 2D Transformation What’s local coordinate ? ? 79

Composite 2D Transformation What’s the current coordinate A ? ? 80

Composite 2D Transformation What’s the current coordinate A ? ? 81

Composite 2D Transformation What’s the current coordinate A ? ? 82

Composite 2D Transformation What’s the current coordinate A ? ? 83

Composite 2D Transformation What’s the current coordinate A ? 84

How to Animate the Character? A 2D lamp character 85

How to Animate the Character? Keyframe animation - Manually pose the character by choosing appropriate values for - Linearly interpolate the inbetween poses. - Works for any types of articulated characters! 86

3D Transformation A 3D point (x,y,z) – x,y, and z coordinates We will still use column vectors to represent points Homogeneous coordinates of a 3D point (x,y,z,1) Transformation will be performed using 4x4 matrix 87

Right-handed Coordinate System Left hand coordinate system Not used in this class and Not in OpenGL 88/94

3D Transformation Very similar to 2D transformation Translation transformation Homogenous coordinates 89

3D Transformation Very similar to 2D transformation Scaling transformation Homogenous coordinates 90

3D Transformation 3D rotation is done around a rotation axis Fundamental rotations – rotate about x, y, or z axes Counter-clockwise rotation is referred to as positive rotation (when you look down negative axis) x y z + 91

3D Transformation Rotation about z – similar to 2D rotation x y z + 92

3D Transformation Rotation about y: z -> y, y -> x, x->z y z x x y z 93

3D Transformation Rotation about x (z -> x, y -> z, x->y) x y z z x y 94

Inverse of 3D Transformations Invert the transformation In general, X= AX’->x’=A -1 X T(t x,t y,t z ) T(-t x,-t y,-t z )

3D Rotation about Arbitrary Axes Rotate p about the by the angle 96

3-D Rotation General rotations in 3-D require rotating about an arbitrary axis of rotation Deriving the rotation matrix for such a rotation directly is a good exercise in linear algebra The general rotation matrix is a combination of coordinate-axis rotations and translations! 97

3D Rotation about Arbitrary Axes Rotate p about the by the angle 98

3-D Rotation General rotations in 3-D require rotating about an arbitrary axis of rotation Deriving the rotation matrix for such a rotation directly is a good exercise in linear algebra Standard approach: express general rotation as composition of canonical rotations  Rotations about x, y, z 99

Composing Canonical Rotations Goal: rotate about arbitrary vector r by θ  Idea: we know how to rotate about x,y,z  Set up a transformation that superimposes rotation axis onto one coordinate axis  Rotate about the coordinate axis  Translate and rotate object back via inverse of the transformation matrix 100

Composing Canonical Rotations Goal: rotate about arbitrary vector r by θ  Idea: we know how to rotate about x,y,z  So, rotate about z by -  until r lies in the xz plane  Then rotate about y by -β until r coincides with +z  Then rotate about z by θ  Then reverse the rotation about y (by β )  Then reverse the rotation about z (by  ) 101

3D Rotation about Arbitrary Axes Rotate p about the by the angle 102

3D Rotation about Arbitrary Axes Translate so that rotation axis passes through the origin 103

3D Rotation about Arbitrary Axes Rotation by about z-axis 104

3D Rotation about Arbitrary Axes Rotation by about y-axis 105

3D Rotation about Arbitrary Axes Rotation by about z-axis 106

3D Rotation about Arbitrary Axes Rotation by about y-axis 107

3D Rotation about Arbitrary Axes Rotation by about z-axis 108

3D Rotation about Arbitrary Axes Translate the object back to original point 109

3D Rotation about Arbitrary Axes Final transformation matrix for rotating about an arbitrary axis 110

3D Rotation about Arbitrary Axes Final transformation matrix for rotating about an arbitrary axis 111

3D Rotation about Arbitrary Axes Final transformation matrix for rotating about an arbitrary axis

3D Rotation about Arbitrary Axes Final transformation matrix for rotating about an arbitrary axis A 3 by 3 Rotation matrix—orthogonal matrix

Rotation Matrices Orthonormal matrix:  orthogonal (columns/rows linearly independent)  normalized (columns/rows length of 1) 114

Rotation Matrices Orthonormal matrix:  orthogonal (columns/rows linearly independent)  normalized (columns/rows length of 1) The inverse of an orthogonal matrix is just its transpose: 115

Rotation Matrices Orthonormal matrix:  orthogonal (columns/rows linearly independent)  normalized (columns/rows length of 1) The inverse of an orthogonal matrix is just its transpose: 116

Rotation Matrices Orthonormal matrix:  orthogonal (columns/rows linearly independent)  normalized (columns/rows length of 1) The inverse of an orthogonal matrix is just its transpose: 117

Why? Rotation Matrices 118

Why? Rotation Matrices 119

Why? Rotation Matrices 120

Why? Rotation Matrices 121

Rotation Matrices Orthonormal matrix:  orthogonal (columns/rows linearly independent)  normalized (columns/rows length of 1) The inverse of an orthogonal matrix is just its transpose: e.g., 122

3D Coordinate Transformation Transform object description from to p 123

2D Coordinate Transformation Transform object description from to p 124

3D Coordinate Transformation Transform object description from to p 125

3D Coordinate Transformation Transform object description from to p 126

3D Coordinate Transformation Transform object description from to 127 p

3D Coordinate Transformation Transform object description from to 128 x y z

Composite 3D Transformation Similarly, we can easily extend composite transformation from 2D to 3D 129

Composite 3D Transformation 130