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.