Graphics_3D viewing

All the information regarding 3D viewing is here. The whole presentation consists mainly of 3D viewing pipeline. This slide will make you clear about how one can have a 3d viewing of an object.

1. 3D viewing Presented by: Rabin BK BSc.CSIT 4 th Semester

2. CONTENTS 3-D viewing pipeline References

3. The viewing-pipeline in 3 dimensions is almost the same as the 2D-viewing-pipeline An additional projection step is done, which is the reduction of 3D-data onto a projection plane after the definition of the viewing direction and orientation 3D viewing pipeline

4. Step 1 & 2: Object Coordinates and World-Coordinates World Coordinate System Viewing Coordinate System

5. To convert world-coordinates to viewing-coordinates a series of simple transformations is needed. Mainly a translation of the coordinate origins onto each other and afterwards 3 rotations, such that the coordinate-axes also coincide (two rotations for the first axis, one for the second axis, and the third axis is already correct then). All these transformations can be merged by multiplication into one matrix, which looks about like this: Step 3: Viewing-Coordinates

6. Step 4: P rojection of object to viewing plane View Plane Parallel Projection Coordinate are transferred to viewing plane along parallel lines. Preserves relative size of object’s portions. Projection can be perpendicular or oblique to viewing plane.

7. Step 4: P rojection of object to viewing plane contd.. Perspective Projection Projection lines converge in a point behind viewing plane. Doesn’t preserve relative size but looks more realistic. View Plane Vanishing point

8. Step 4: P rojection of object to viewing plane contd.. Orthogonal (orthographic) projections Projection lines are parallel to normal. Used in engineering and architecture. Length and angles can be measured directly from drawings. Plane View Side Elevation View Front Elevation View

9. Step 5: Clipping Window and View Volume Orthogonal Projection View Volume Far Clipping Plane Near Clipping Plane View Plane Clipping window Before projecting, we need to eliminate the portion of scene that is outside the viewing frustum Need to clip objects to the frustum (truncated pyramid)

10. This coordinate system refers to a subset of the screen space where the model window is to be displayed. Typically the viewport will occupy the entire screen window, or even the entire screen, but it is also possible to set up multiple smaller viewports within a single screen window. The normalized view volume cube extending from 1, 1, 1 to -1, -1, -1 is mapped to a screen viewport, extending from xv min , yv min to xv max , yv max Step 6: 3D Viewport Transformation

11. Step 6: 3D Viewport Transformation The normalized view volume cube extending from 1, 1, 1 to -1, -1, -1 is mapped to a screen viewport, extending from xv min , yv min to xv max , yv max

12. R eferences https://www.cs.uic.edu/~jbell/CourseNotes/ComputerGraphics/Coordinates.html http://www.di.ubi.pt/~agomes/cg/teoricas/05e-viewing.pdf https://www.cs.drexel.edu/~david/Classes/CS430/Lectures/L-12_Intro3DViewing.6.pdf https://www.cs.cmu.edu/afs/cs/academic/class/15462-s09/www/lec/06/lec06.pdf

13. Queries