In this paper, Tracy unleashes LADDER unto the world. LADDER is a sketching language, designed to describe sketches as combinations of geometric primitives following geometric constraints. A primitive shape is one that cannot be broken down into simpler shapes, for example a line- or arc-segment. Geometric constraints define how shapes interact with the world and with each other. For example, a constraint might describe one line as horizontal or two lines as perpendicular.
LADDER builds complex shapes up from combinations of simpler shapes, simultaneously tackling the grouping and recognition problems. The downside to this approach is that putting a large number of primitives on the screen will cause an exponential runtime explosion, which has been known to injure innocent bystanders with recursively-enumerable shrapnel.
Tracy notes that LADDER works well for shapes that can be described in terms of geometric primitives, especially shapes that don't have too much detail. How, then, should we deal with detailed shapes? This is one area of consideration for the current assignment. Is there a general way of approaching detailed shapes, or does each shape require custom-tailored recognition techniques?
I think the next reading (#12) addresses that. I'm betting successful recognition of complex shapes is NP-Hard. This is just supposition, but if anyone has any details regarding this, please share.
ReplyDeleteWhether a shape can be recognized in LADDER is determined by whether users can explicitly describe the shape. For complicated shapes, I guess, it is also difficult for users to describe exactly, like what a cat is like. So LADDER is just to recognize what users can exactly describe.
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