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Sample Final Exam
CMSC 427, Fall 2001
Time Limit: 120 minutes, Maximum Marks: 100 Open book, open notes
Name:
UMD Id:
Note: This exam has two pages. Please make sure you have both of them. If the meaning of a question is doubtful, state a meaningful, non-trivial as- sumption and proceed. Advice: To maximize partial credit, divide your time as per the minutes shown. Point value of each question equals its recommended time value in minutes.
Important: This is a sample final exam that covers the topics after the midterm. The real final exam will have more questions to ensure a better coverage of topics before and after the midterm that we have covered in the class. This paper has questions worth 55 minutes instead of the target 100 minutes. The general level of difficulty will be approximately what you see here.
Q.1 [ 8 × 5 = 40 minutes] (i) Perspective foreshortening occurs for textures and we discussed a couple of methods in the class to overcome it. Does perspective foreshortening also occur for shading under perspective projection? If yes, why doesn’t anyone try to address it using methods similar to those used in texturing? If not, why not, when linear interpolation for (u, v) coordinates across a triangle matches linear interpolation for (r, g, b) coordinates?
(ii) Assume that the viewer and the light source are both located at z = ∞ above a terrain with identical vertex normals. Assuming identical material and light colors for ambient, diffuse, and specular, no attenuation or spot- light factors, and Gouraud shading, which of the following illuminations will
be rendered as identical: (a) Ambient-only, (b) Diffuse-only, (c) Specular- only. If we change the shading from Gouraud to Phong, keeping the other parameters the same, which of the above illuminations (a), (b), (c) will be rendered identically?
(iii) What is the difference between back-plane culling and back-face culling?
(iv) Name a tracking technology for virtual environments that can work over large (potentially unrestricted) volumes.
(v) Ray tracing and radiosity are two methods for global illumination. List one advantage of ray tracing over radiosity and one advantage of radiosity over ray tracing
(vi)How can the convex-hull containment property of Bezier curves (and also of surfaces) be useful in collision detection?
(vii) What is the advantage of procedural textures over image-based tex- tures?
(viii) If a line is being drawn with RGB = (180, 200, 10) at end point A and RGB = (90, 260, 40) at end point B, what will be the RGB value of a point C that is between A and B and is twice as far from A as B? Assume that the line is being drawn under parallel projection and the colors are computed using linear interpolation.
Q.2 [ 2 × 7 .5 = 15 minutes] (i) Some researchers in graphics have claimed that 2 K (2048) uniformly distributed normals are sufficient for generating reasonably realistic illumination for large scenes. Assuming this is true, let us further assume that the viewer and the light source are both at infinity. How can you take advantage of these assumptions to speed up the illumination computations for each vertex?
(ii) You have been asked to render two iso-surfaces of a volume dataset of a person: one corresponding to the muscles and the second corresponding to the bones. Let us assume that the muscles occur at the density 120 and the bones at the density 200. We will like the muscles to appear in red and the bones in white. Show the RGBA transfer functions that will accomplish this.
