COMMENTS:
SUMMARY:
LADDER is a sketch description language that describes how shapes are drawn and edited. This paper gives an overview of LADDER and shows how it can be used to develop a sketch interface. LADDER relies on both soft and hard constraints to facilitate recognition; soft constraints can include factors such as drawing order whereas hard constraints can be geometric constraints.
Shapes are categorized using the subcomponents of the shape, its geometric constraints, aliases for the parts of the shape, editing gestures and display methods. The hard constraints areas are the basis for the predefined constraints used to create LADDER.
DISCUSSION:
This gives a good explanation of LADDER and how it uses constraints to create shape definitions in order to classify strokes as specific shapes within a domain. I think anyone who’s programmed (or completed the last assignment for this class) could appreciate a language that can classify stroke relationship or characteristics in simple text such as “line1 intersects line2”.
One challenge to LADDER that I found interesting was the task of trying to identify incomplete shapes on the screen while the sketch is still in progress. Depending on how complicated the sketch is, unrecognized strokes can slow down the recognizer. I would think that most people would want to complete a shape they’re working on before moving on to another one. Instant feedback showing that a stroke is unrecognized would discourage the user from moving on until it’s complete.
I think the best thing to do is to shock users repeatedly until they finish their unrecognized symbols! That way they will never jump around (unless the shocks cause them to jerk their hand, thus resulting in more shocks).
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