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CS689, Winter 2001, Activity instructions, Week 12

CS689, Winter, 2001

Activity instructions, Week 12


Make a line drawing from an original having available only a limited field of view.

In this lecture, which looks more toward the limits of current user interface techniques we will be looking at two issues:

  1. How state and history representations interact in user interfaces, and
  2. How to deal with limited bandwidth in the input/output of an interface.
To give you a feel for what is involved in this I have looked for an activity that is normally done using a state representation, and having you do it using a history representation. The activity is reproducing a drawing. The hard part of copying a drawing, once we get beyond the technical control of the pencil (which is the limit for people like me), is getting the different parts of the drawing in the right spatial relationship to one another. To do so, we are constantly needing to look at the drawing as a whole, seeing what is where.

For this activity you are going to copy a drawing that is about eight inches square, but without being able to look at more than about two inches at a time. How is this limitation imposed? By looking through a mask, and the easiest way to impose a mask is to get you to look through a tube four or five centimetres in diameter. So find a tube from a paper towel roll, and cut it to be about fifteen to twenty centimetres long. Hold it in front of one of your eyes with your non-dominant hand. Close the other eye and look through the tube at the drawing you are copying, while drawing holding the pencil in your dominant hand. You will probably need to do something to hold the paper on which you are drawing fixed in place, which adds another constraint to the drawing process, which is ordinarily a two-handed activity: one hand orienting and positioning the paper, one hand moving the pencil. (Drawing differs from drafting primarily in how the paper is managed.)

Choose a drawing to copy, the "original". It should be about 20 cm square, and can be continuous tone or line art. Your verison should be just line art, done with an ordinary HB pencil, and it should be the same size as the original. Feel free to move back and take a look at either original or copy from a distance to see how you are coming along. Move back even farther and look at both original and copy if you like. (The tube is supposed to be long enough that you can't do any drawing while you are in the "zoomed back" state.)

The essence of this activity is to notice how you work serially to build up the holistic perception that you can get by looking at the entire drawing at once under normal conditions. That it is not easy to do is a bit counter-intuitive. We have good sharp detailed vision only in the fovea, the central two degrees of the visual field: the viewing arrangement you have does not obscure any part of foveal vision! We move the fovea from place to place in order to build up the detailed perception of complex objects. But there must be much more going on in normal vision; peripheral vision must play an important role in locating the detailed area in the right location relative to perceptions that occur before and after it.

While you are doing the drawing think about the following things.

  1. You have available two operations, pan and zoom, that are easy to implement with your viewer. When do you use each of them? And when you use them what aspects are you trying to draw and what features of the original are you trying to perceive?
  2. Are there operations other than pan and zoom that you can do? that you would like to do?
  3. Pan and zoom are almost always inplemented in graphical programs, where the user looks at the world through a relatively small window. What other operations do you see in graphical interfaces? Are there ideas you had from the question above that might be useful for graphical interfaces?
  4. Are you using the same field of view when monitoring your drawing as you use when perceiving what to draw next?
  5. Not monitoring the drawing as it develops is a technique taught in many art and design classes. That is, you are told to draw without looking at what you are drawing, only looking at the thing being drawn. Is this a useful way to improve performance when working with a restricted field of view?

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