Sketchpad: A Man-machine Graphical Communiction System

Ivan E. Sutherland

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ben's blog

Summary

Sutherland presents a new (in 1963) graphical communication system called Sketchpad that uses a pen interface instead of a keyboard. Using a light pen and a set of push buttons, a person can create drawings on a computer using Sketchpad.

Sketchpad uses a ring structure to store relationships between elements in a drawing. Elements are structured in a hierarchy where ancestors are more generic than their descendants. This allows for separation of generic and element specific code, not too unlike modern OOP. Sketchpad supports the addition of new element types as well.

Sketchpad supports the display of not only graphical elements, but also abstractions. An example of an abstraction is a constraint block, which is a rule that specifies certain values must be maintained (e.g. making lines parallel). By visualizing these abstractions, Sketchpad allows the user to make changes to them.

Several atomic operations, controlled by the push buttons, provide for the creation of new drawing elements in the display. One of these operations, the copy function, lets the user create a new instance of an existing element, referred to as a "definition picture." Definition pictures can contain "attachers," that are used in relating the definition picture to other elements. Copied instances are linked to each other, so a change to one affects the others. Using this copy functionality large patterns can easily be created and modified.

Sunderland used Sketchpad for a number of different applications including linkages, bridge structural diagrams, animation, and electrical circuit diagrams.

Discussion

This paper is obviously significant for being the first to use a pen interface, a ground breaking achievement, which was sadly not followed up on until much later. This work combines human drawing with the computer's mathematical computation. Sketchpad allows a person to apply real world constraints to a design drawing that isn't possible with pen and paper.

I found two faults with this work. The first is using a flick to terminate. A flick being, as described in the paper, a quick movement too fast for tracking program to recognize. Since the system is using the pen and paper metaphor, I think terminate should be done my moving the pen away from the display, but perhaps hardware limitations prevented them from doing so. The second is the use of push buttons. I realize hardware limitations may have necessitated this design decision, but that type interaction does not match the fluidity I feel when just using pen and paper. It does remind me of some recent work I've seen that uses bimanual pen and and direct-touch for interaction. Not the same idea, but similarities in using both hands with a pen in one.

My one question is,"where's the user study?" Perhaps it is just my HCI background that begs this question. Not that the paper needs a user study. It's innovative, that's enough a reason for writing about it. It seems that potentially more people would have pursued this approach had some evaluation shown that this work was an improvement over other interfaces.

The future work for me is fixing the problems described and evaluating the system.