3D Transformation in Computer Graphics

Transformation:
Transformations are a fundamental part of the computer graphics. Transformations are the movement of the object in Cartesian plane.
Types of transformation
Why we use transformation
3D Transformation
3D Translation
3D Rotation
3D Scaling
3D Reflection
3D Shearing

1. World University Of Bangladesh

2. INTRODUCTION Here we introduce to about 3D Transformation

3. OBJECTIVE

4. Transformations are a fundamental part of the computer graphics. Transformations are the movement of the object in Cartesian plane . Transformation

5. Transformation are used to position objects , to shape object , to change viewing positions , and even how something is viewed. In simple words transformation is used for 1) Modeling 2) viewing Why we use transformation

6. Three Dimensional Transformations When the transformation takes place on a 3D plane , it is called 3D transformation. Methods for object modeling transformation in three dimensions are extended from two dimensional methods by including consideration for the z coordinate.

7. Three Dimensional Modeling Transformations Generalize from 2D by including z coordinate Straightforward for translation and scale, rotation more difficult Homogeneous coordinates: 4 components Transformation matrices: 4×4 elements

8. 3D Transformation . Simple transformation Complex & Conjugate transformation Translation Rotation Scaling Reflection Shearing 3D Transformation

9. 3D Point We will consider points as column vectors. Thus, a typical point with coordinates (x, y, z) is represented as:

10. 3D Point Homogenous Coordinate We don't lose anything The main advantage: it is easier to compose translation and rotation Everything is matrix multiplication

11. 3D Coordinate Systems Right Hand coordinate system: Left Hand coordinate system:

12. 3D Transformation In homogeneous coordinates, 3D transformations are represented by 4×4 matrixes:

13. TRANSLATION

14. 3D translation An object is translated in 3D dimensional by transforming each of the defining points of the objects. Moving of object is called translation. In 3 dimensional homogeneous coordinate representation , a point is transformed from position P = ( x, y , z) to P’=( x’, y’, z’) This can be written as:- Using P’ = T . P

15. 3D translation The matrix representation is equivalent to the three equation. x’=x+ t x , y’=y+ t y , z’=z+ t z Where parameter t x , t y , t z are specifying translation distance for the coordinate direction x , y , z are assigned any real value. Translate an object by translating each vertex in the object.

16. ROTATION

17. 3D Rotation In general, rotations are specified by a rotation axis and an angle. In two-dimensions there is only one choice of a rotation axis that leaves points in the plane.

18. 3D Rotation The easiest rotation axes are those that parallel to the coordinate axis. Positive rotation angles produce counterclockwise rotations about a coordinate axix , if we are looking along the positive half of the axis toward the coordinate origin. fig: 3D rotation

19. Coordinate Axis Rotations Obtain rotations around other axes through cyclic permutation of coordinate parameters: Fig:Coordinate Axis Rotations

20. Coordinate Axis Rotations Z-axis rotation: For z axis same as 2D rotation : x’=x* cos θ -y*sin θ Y’=x*sin θ +y* cos θ Z’=z Fig : Z-axis rotation

21. Coordinate Axis Rotations X-axis rotation : Y’=y* cos θ -z*sin θ Z’=z*sin θ +x* cos θ X’=x Fig : X-axis rotation

22. Coordinate Axis Rotations Y-axis rotation: Z’=z* cos θ -x*sin θ X’=z*sin θ +x* cos θ Y’=y Fig : Y-axis rotation

23. SCALING

24. 3D Scaling You can change the size of an object using scaling transformation . In the scaling process , you either expand or compress the dimensions of the object . Scaling can be achieved by multiplying the original coordinates of the object with scaling factor to get the desired result.

25. 3D Scaling About origin: Changes the size of the object and repositions the object relative to the coordinate origin . where Sx = scale factor in the x direction, Sy = scale factor in the y direction, and Sz = scale factor in the z direction. Fig: Scaling

26. 3D Scaling About any fixed point : Scaling with respect to an arbitrary fixed point is not as simple as scaling with respect to the origin . The procedure of scaling with respect to an arbitrary fixed point is: Translate the object so that the fixed point coincides with the origin. Scale the object with respect to the origin. Use the inverse translation of step 1 to return the objects to its original position.

27. 3D Scaling About any fixed point: fig : fixed point scaling The corresponding composite transformation matrix is:

28. 3d scaling The equations for scaling : x’ = x . sx S sx,sy,sz  y’ = y . sy z’ = z . sz fig name: After scaling

29. REFLECTIONS

30. 3D Reflections About an axis: equivalent to 180 ˚ rotation about that axis.

31. 3D reflection Reflection in computer graphics is used to emulate reflective objects like mirrors and shiny surfaces. Reflection may be an x-axis y-axis , z-axis. and also in the planes xy - plane,yz -plane , and zx -plane. Reflection relative to a given Axis are equivalent to 180 Degree rotations . Fig: reflection

32. 3d reflection Reflection about x-axis:- x’=x y’=-y z’=-z 1 0 0 0 0 -1 0 0 0 0 -1 0 0 0 0 1 Reflection about y-axis:- y’=y x’=-x z’=-z Fig: X axis reflection Fig:Y axis reflection

33. 3D reflection The matrix for reflection about y-axis:- -1 0 0 0 0 1 0 0 0 0 -1 0 0 0 0 1 Reflection about z-axis:- x’=-x y’=-y z’=z -1 0 0 0 0 -1 0 0 0 0 1 0 0 0 0 1 Fig: Z axis reflection

34. SHEARING

35. 3D Shearing A transformation that distorts the shape of an object such that the transformed shape appears as if the object were composed of internal layers that had been caused to slide over each other is called a shearing.

36. 3D Shearing In two dimensions, transformations relative to the x or y axes to produce distortions in the shapes of objects. In three dimensions, we can also generate shears relative to the z axis. fig: before shearing fig: after shearing

37. 3D Shearing Modify object shapes Useful for perspective projections: E.g. draw a cube (3D) on a screen (2D) Alter the values for x and y by an amount proportional to the distance from z ref

38. SHEARING ABOUT XY AXIS Parameters a and b can be assigned any real values. The effect of this transformation matrix is to alter x- and y-coordinate values by an amount that is proportional to the z value, while leaving the z coordinate unchanged. Boundaries of planes that are perpendicular to the z axis are thus shifted by an amount proportional to z. An example of the effect of this shearing matrix on a unit cube is shown in Fig., for shearing values a=b=1. Shearing matrices for the x axis and y axis are defined similarly.

39. In space, we divide shear transformation according to the direction of the surfaces xy,xz and yz . Values of Sx,Sy and Sz determine shear transformation sizes for all the directions. A shear transformation about the xy plane :       | 1  0 0 0 |       Axy =   |  0  1 0 0 | | Sx Sy 0 0|       |  0  0 0 1 | A shear matrix about the xz plane :        |  1  0  0  0 |     Axz =     | Sx   1 Sz   0| |  0  1  1  0 |        |  0  0  0  1 | A shear matrix about the yz plane :        | 1 Sy Sz 0 |       | 0  1  0 0 | Ayz = | 0  0  1 0 |      | 0  0  0 1 |

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