Introduction
LADDER is a system for describing and recognizing hand drawn shapes using a human readable geometric description language. This is meant to allow system designers to create sets of shapes that can be recognized as part of a visual grammar, that is a certain domain. In addition to shape recognition, LADDER also allows designers to describe how recognized shapes should be displayed, what actions can be performed on them or what actions they perform on other shapes.
Shape structures can be made up of basic recognition shapes, such as lines, poly-lines, circles etc. as well as previously defined shapes. Constraints can then be placed on the relationships between these subshapes.
The system uses these descriptions in a bottom up approach, starting with identifying basic shapes from strokes, constructing many higher level shapes from each basic shape. Eventually each shape is part of one high level shape.
Discussion
LADDER is very useful for domains with simple geometric shapes that are easy to describe either individually or as part of a hierarchy. This becomes problematic with more complex individual shapes that are hard to describe. It might be interesting, as mentioned in LADDER's future work, if a designer could automatically generate a LADDER description of a complex shape, both to make it easier on the designer and to show which shapes might be problematic for LADDER to describe at all. In such cases it would seem useful if a designer could use some other manner of recognition to describe a particular shape, but could then use that shape in a later LADDER description. This way LADDER could incorporate more complex shapes while still keeping the geometric descriptions to create composite complex shapes.
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