SEM540b. Graphics and HCI
Class Exercise for Week 5. Specimen Examination Questions.
Each Examination question should take 30-45 minutes. Choose two from the following list and prepare solutions to be discussed in the following lecture.
Specimen Examination Questions for Computer Graphics. 1. Describe, using suitable equations and diagrams, the three transformations discussed in your two-dimensional computer graphics course. Give an example of each. Describe the GKS normalisation transformations to take a diagram described in world coordinates and map it on to the corresponding diagram in device coordinates. As an example, take the window in world coordinates defined by xmin = 0.0, xmax = 100.0, ymin = 0.0 and ymax = 80.0 and show how the point P (20,60) is affected by the GKS output. Assume you are displaying your output on a VGA screen with 640 pixels from left to right in the x-direction and 480 pixels from top to bottom in the y-direction. 2. A diagram consists of a polygon defined by listing the coordinates of its vertices in order around the polygon. Explain in general how you would decide whether any other point (x,y) lies inside or outside this polygon. Illustrate the method you have described by calculating whether the following three points lie inside or outside the polygon whose vertices are: A(30,60), B(90,70), C(70,140), D(80,30), E(40,10) and F(15,30). (i) P1 (10,90). (ii) P2 (40,40). (iii) P3 (80,40). Assume that you have a routine Floodfill(x,y,c) which will fill a polygon with the colour c starting from the seed point (x,y). Discuss whether the polygon defined above will require one or more seed-points (and hence callls to the routine) and show how to obtain suitable seed-point(s). What are the restrictions on this approach in general ? 3. A picture in a cell-array, bham2, contains the following values: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 6 1 1 6 6 1 1 1 1 1 1 1 1 1 1 6 1 1 6 6 6 1 1 1 1 1 1 1 1 1 6 1 6 6 6 6 6 1 1 1 6 1 1 1 1 6 6 6 6 6 6 6 1 1 6 6 1 1 1 1 1 1 6 6 6 6 6 6 6 6 6 1 1 1 1 1 1 6 6 6 6 6 6 6 6 1 1 1 1 1 1 1 6 6 6 6 1 6 6 1 1 1 1 1 1 1 1 1 6 6 1 1 1 1 1 1 1 1 1 1 1 1 6 6 6 6 1 1 1 1 1 1 1 1 1 1 1 6 6 6 6 1 1 1 1 1 1 1 1 1 1 1 6 6 6 6 1 1 1 1 1 1 1 1 1 1 1 1 6 6 6 1 6 6 6 1 1 1 1 1 1 1 1 1 6 6 6 6 6 6 1 1 1 1 1 1 1 1 1 1 6 6 6 6 1 6 6 6 1 1 1 1 1 1 1 1 1 1 6 6 6 6 1 1 1 1 1 1 1 1 1 1 1 1 6 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 where 1 produces a blue pixel and 6 produces a yellow one. (a) Describe how this image could be represented using run-length encoding and illustrate your method by generating the code for this image. (b) Given a GKS implementation where a window in world coordinates of 100x100 is mapped on to a screen 600x400 pixels, describe the result of the following cell-array calls. (i) CellArray(P1,P2,15,18,bham2) where P1 is (10.0,10.0) and P2 is (14.0,16.0). (ii) The same call where P1 is (12.0,16.0) and P2 is (14.667,20.5). (iii) The same call where P1 is (14.0,14.0) and P2 is (16.667,18.0). Specimen Examination Questions for H.C.I. 4. (a) Any succesful interface between human and computer has to find the common ground between two systems which differ greatly in properties such as size and speed. Describe the constraints imposed on this interface by the limits of human perception and memory. (b) It has been decided that an annual questionnaire collecting feedback from stuudents will be automated. Since student numbers are large and time is limited, all available terminals must be used. Some are colour and others monochrome, some have graphics and others only text, most have a full WIMP interface but a few have only screen and keyboard. Assuming an identical interface is required on every terminal in the system, identify the constraints on this common interface. (c) The aim of the questionnaire is to carry out a comparative survey of the lecture courses within the school as perceived by the students. It will cover topics such as the content of the course and its relevance to the subject as a whole, the standard of teaching and the availability of other resources needed for this course. You may also include questions on additional aspects that you consider important. Give a detailed description of the interface, remembering that it should be easy to understand and use and must comply with the constraints identified in (a) and (b). (d) How would your design differ if you had a free choice of system on which to run this questionnaire? 5. a) One of the methods which attempt to make personal computer systems more “friendly” is the provision of handwritten input. This software is a subset of the much larger problem of handwriting recognition in general. Describe the main difference between “on-line” and “off-line” handwriting recognition and explain the effect this difference has on the resulting systems. b) Describe in detail a possible system for handwritten input using a tablet and stylus. Your proposed system should consider the following questions: Will your system recognise letters or words and how will it do this? Will it recognise cursive handwriting? Can it be used by several different people or is it restricted to just one user? (c) Normally the security of such systems is assured by requiring a password to be entered at the start of each session. Is it practical for your system to recognise a signature instead? 6. Provide a structured description of the icons used by your favourite word-processor. Were they obvious to you when you first started using it? Suggest improved icons for some of the functions (explain why your improved icon is an improvement). Would you expect others to see things in the same way? (i.e. to what extent is your choice of icon determined by your personal history and what percentage of users would you expect to share the relevant parts of this background?) 7. The main problems of human-computer interaction arise because of the differing abilities of the two participants. Comment on these differences in each of the following area and explain how a compromise may be reached when defining an interface: (a) memory. (b) I/O channels. (c) response time. (d) size.