Easy presentation for college students on 3-D Computer Graphics

1. Three Dimensional Graphics
The three-dimensional transformations are extensions of two-
dimensional transformation. In 2D two coordinates are used, i.e.,
x and y whereas in 3D three co-ordinates x, y, and z are used.
For three dimensional images and objects, three-dimensional
transformations are needed. These are translations, scaling, and
rotation. These are also called as basic transformations are
represented using matrix. More complex transformations are
handled using matrix in 3D.

2. 3D Geometry
Three dimension system has three axis x, y, z. The orientation
of a 3D coordinate system is of two types. Right-handed system
and left-handed system.
Using right-handed system co-ordinates of corners A, B, C, D
of the cube
Point A x, y, z
Point B x, y, 0
Point C 0, y, 0
Point D 0, y, z

3. Translation
 It is the movement of an object from one position to another position. Translation
is done using translation vectors. There are three vectors in 3D instead of two.
These vectors are in x, y, and z directions.
 Matrix representation of point translation.
 Point shown in fig is (x, y, z). It become (x1,y1,z1) after translation. Tx Ty Tz are
translation vector

4. Example:-
A point has coordinates in the x, y, z direction i.e., (5, 6, 7). The translation is
done in the x-direction by 3 coordinate and y direction. Three coordinates and in
the z- direction by two coordinates. Shift the object. Find coordinates of the new
position.
Solution: Co-ordinate of the point are (5, 6, 7)
Translation vector in x direction = 3
Translation vector in y direction = 3
Translation vector in z direction = 2
Translation matrix is
Multiply co-ordinates of point with translation matrix
x becomes x1=8
y becomes y1=9
z becomes z1=9

5. Scaling
Scaling is used to change the size of an object. The size can be increased or decreased. The
scaling three factors are required Sx Sy and Sz.
Sx=Scaling factor in x- direction
Sy=Scaling factor in y-direction
Sz=Scaling factor in z-direction
Matrix for Scaling-

6. Example:-
Given a 3D object with coordinate points A(0, 3, 3), B(3, 3, 6). Apply the scaling
parameter 2 towards X axis, 3 towards Y axis and 3 towards Z axis and obtain the
new coordinates of the object.
Solution :- Given-
Old coordinates of the object = A (0, 3, 3), B(3, 3, 6).
Scaling factor along X axis = 2
Scaling factor along Y axis = 3
Scaling factor along Z axis = 3
For Coordinates A(0, 3, 3)
Let the new coordinates of A after scaling = (Xnew, Ynew, Znew).
Xnew = Xold x Sx = 0 x 2 = 0
Ynew = Yold x Sy = 3 x 3 = 9
Znew = Zold x Sz = 3 x 3 = 9
Thus, New coordinates of corner A after scaling = (0, 9, 9).

7. For Coordinates B(3, 3, 6)
Let the new coordinates of B after scaling = (Xnew, Ynew, Znew).
Xnew = Xold x Sx = 3 x 2 = 6
Ynew = Yold x Sy = 3 x 3 = 9
Znew = Zold x Sz = 6 x 3 = 18
Thus, New coordinates of corner B after scaling = (6, 9, 18).

8. Rotation
It is moving of an object about an angle. Movement can be anticlockwise or clockwise. 3D
rotation is complex as compared to the 2D rotation. For 2D we describe the angle of
rotation, but for a 3D angle of rotation and axis of rotation are required. The axis can be
either x or y or z.

9. Matrix for representing three-dimensional rotations about the Z axis
Matrix for representing three-dimensional rotations about the X axis
Matrix for representing three-dimensional rotations about the Y axis

10. Example:-
Given a homogeneous point (1, 2, 3). Apply rotation 90 degree towards X, Y and Z axis and find
out the new coordinate points.
Solution :- Old coordinates = (Xold, Yold, Zold) = (1, 2, 3) Rotation angle = θ = 90º
For X-Axis Rotation-
Xnew = Xold = 1
Ynew = Yold x cosθ – Zold x sinθ = 2 x cos90° – 3 x sin90° = 2 x 0 – 3 x 1 = -3
Znew = Yold x sinθ + Zold x cosθ = 2 x sin90° + 3 x cos90° = 2 x 1 + 3 x 0 = 2
Thus, New coordinates after rotation = (1, -3, 2).0
For Y-Axis Rotation-
Xnew = Zold x sinθ + Xold x cosθ = 3 x sin90° + 1 x cos90° = 3 x 1 + 1 x 0 = 3
Ynew = Yold = 2
Znew = Yold x cosθ – Xold x sinθ = 2 x cos90° – 1 x sin90° = 2 x 0 – 1 x 1 = -1
Thus, New coordinates after rotation = (3, 2, -1).
For Z-Axis Rotation-
Xnew = Xold x cosθ – Yold x sinθ = 1 x cos90° – 2 x sin90° = 1 x 0 – 2 x 1 = -2
Ynew = Xold x sinθ + Yold x cosθ = 1 x sin90° + 2 x cos90° = 1 x 1 + 2 x 0 = 1
Znew = Zold = 3
Thus, New coordinates after rotation = (-2, 1, 3).

11. Reflection
It is also called a mirror image of an object. For this reflection axis and
reflection of plane is selected. Three-dimensional reflections are similar to
two dimensions. Reflection is 180° about the given axis. For reflection,
plane is selected (xy,xz or yz). Following matrices show reflection respect to
all these three planes
Reflection relative to XY plane

12. Matrix For XYCoordinates :-
Reflection relative to YZ plane
Reflection relative to XZ plane
Example:-
Given a 3D triangle with coordinate points A(3, 4, 1), B(6, 4, 2), C(5, 6, 3). Apply the
reflection on the XY plane and find out the new coordinates of the object.
Solution- Given:-Old corner coordinates of the triangle = A (3, 4, 1), B(6, 4, 2), C(5, 6,
3)
Reflection has to be taken on the XY plane

13. For Coordinates A(3, 4, 1)
Let the new coordintes of corner A after reflection = (Xnew, Ynew, Znew).
Xnew = Xold = 3
Ynew = Yold = 4
Znew = -Zold = -1
Thus, New coordinates of corner A after reflection = (3, 4, -1)
For Coordinates B(6, 4, 2)
Let the new coordinate of corner B after reflection = (Xnew, Ynew, Znew).
Xnew = Xold = 6
Ynew = Yold = 4
Znew = -Zold = -2
Thus, New coordinates of corner B after reflection = (6, 4, -2).
For Coordinates C(5, 6, 3)
Let the new coordinates of corner C after reflection = (Xnew, Ynew, Znew).
Xnew = Xold = 5
Ynew = Yold = 6
Znew = -Zold = -3
Thus, New coordinates of corner C after reflection = (5, 6, -3).
Thus, New coordinates of the triangle after reflection = A (3, 4, -1), B(6, 4, -2), C(5, 6, -3).

14. Shearing
It is change in the shape of the object. It is also called as deformation. Change can
be in the x -direction or y -direction or both directions in case of 2D. If shear occurs
in both directions, the object will be distorted. But in 3D shear can occur in three
directions
Shearing in X Axis-
Shearing in X axis is achieved by using the following shearing equations-
Xnew = Xold
Ynew = Yold + Shy x Xold
Znew = Zold + Shz x Xold
Shearing in Y Axis-
Shearing in Y axis is achieved by using the following shearing equations-
Xnew = Xold + Shx x Yold
Ynew = Yold
Znew = Zold + Shz x Yold

15. Shearing in Z Axis-
Shearing in Z axis is achieved by using the following shearing equations-
Xnew = Xold + Shx x Zold
Ynew = Yold + Shy x Zold
Znew = Zold
Example:-
Given a 3D triangle with points (0, 0, 0), (1, 1, 2) and (1, 1, 3). Apply shear
parameter 2 on X axis, 2 on Y axis and 3 on Z axis and find out the new
coordinates of the object
Solution-
Old corner coordinates of the triangle = A (0, 0, 0), B(1, 1, 2), C(1, 1, 3)
Shearing parameter towards X direction (Shx) = 2
Shearing parameter towards Y direction (Shy) = 2
Shearing parameter towards Y direction (Shz) = 3
Shearing in X Axis-

16. Coordinates A(0, 0, 0)
Let the new coordinates of corner A after shearing = (Xnew, Ynew, Znew).
Applying the shearing equations, we have-
Xnew = Xold = 0
Ynew = Yold + Shy x Xold = 0 + 2 x 0 = 0
Znew = Zold + Shz x Xold = 0 + 3 x 0 = 0
Thus, New coordinates of corner A after shearing = (0, 0, 0).
For Coordinates B(1, 1, 2)
Let the new coordinates of corner B after shearing = (Xnew, Ynew, Znew).
Applying the shearing equations, we have-
Xnew = Xold = 1
Ynew = Yold + Shy x Xold = 1 + 2 x 1 = 3
Znew = Zold + Shz x Xold = 2 + 3 x 1 = 5
Thus, New coordinates of corner B after shearing = (1, 3, 5).
For Coordinates C(1, 1, 3)

17. Let the new coordinates of corner C after shearing = (Xnew, Ynew, Znew).
Applying the shearing equations, we have-
Xnew = Xold = 1
Ynew = Yold + Shy x Xold = 1 + 2 x 1 = 3
Znew = Zold + Shz x Xold = 3 + 3 x 1 = 6
Thus, New coordinates of corner C after shearing = (1, 3, 6).
Thus, New coordinates of the triangle after shearing in X axis = A (0, 0, 0), B(1,
3, 5), C(1, 3, 6).