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CS689, Winter 2001, Activity instructions, Week 12
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:
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
- How state and history representations interact in user interfaces,
- How to deal with limited bandwidth in the input/output of an
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"
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.
- 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?
- Are there operations other than pan and zoom that you can do? that you
would like to do?
- 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
- Are you using the same field of view when monitoring your drawing as
you use when perceiving what to draw next?
- 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