Page 160 - DCAP504_Computer Graphics

Unit 10: Clipping II

10.5 Self Assessment

1. State whether the following are true or false:
(a) The polygon edges are clipped that lie outside the window boundary.
(b) Parallel projections are the two-dimensional objects that are placed on a three-dimensional
projection plane.
(c) The main rule of all parallel projections is to choose a direction and construct a ray that starts
at a general point on the object and goes in the direction of the plane.
2. Fill in the blanks:
(a) Sutherland-Hodgeman algorithm uses a ………………….. strategy to solve the problem
related to the polygon clipping.
(b) The number of ………………….. that are intersected by the view plane determines the
number of principal vanishing points.
(c) Orthographic projections that show more than one side of an object are called
……………….orthographic projections.
3. Select the suitable choice for every question:
(a) In Weiler-Atherton Algorithm, when the path of traversal forms a………………you output
the sub-polygon as part of the overall result.
(i) Subject polygon

(ii) Clip polygon
(iii) Sub polygon
(iv) Convex polygon
(b) The ……………… is one of the perspective anomalies, where the far the object is from the
center of projection, the smaller it appears.

(i) Perspective foreshortening
(ii) Vanishing points
(iii) View confusion
(iv) Topological distortion
10.6 Review Questions

1. What is polygon clipping? Explain Sutherland-Hodgeman polygon clipping algorithm.
2. Mention the important points that need to be considered in Weiler-Atherton Algorithm.
3. What is projection? Mention the types of projection in computer graphics.
4. What are perspective anomalies?
5. Explain parallel projections.
Answers: Self Assessment

1. (a) True (b) False (c) True
2. (a) Divide-and-conquer (b) Principal axes (c) axonometric
3. (a) Sub polygon (b) Perspective foreshortening

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