Recognizing Free-form Hand-sketched Constraint Network Diagrams by Combining Geometry and Context

Authors: Tracy Hammond, Barry O’Sullivan

Comments:

Summary:
This paper discusses a sketch recognition system developed for Constraint Network diagrams using LADDER.
Author define geometrical recognition rules for nodes, lines , letters and constraints that would be used in the diagram. Example:
The letter V consists of two connecting lines abiding by the
following geometric rules:
1. The "neg" line is negatively or vertically sloped.
2. The "pos" line is positively or vertically sloped.
3. The endpoint "p1" of "pos" line and the endpoint "p1" of
the "neg" line are connected.
4. The endpoint "p2" of "pos" line is above the endpoint
"p1" of the "pos" line.
5. The endpoint "p2" of "neg" line is above the endpoint
"p1" of the "neg" line.
6. The endpoint "p2" of "neg" line is left of the endpoint
"p2" of the "pos" line.
7. The "pos" line and the "neg" line are of equal length.
Contextual rules are then used to further identify V:
1. The "node" contains the center of the "pos" line.
2. The "node" contains the center of the "neg" line.

The system combines the relative and absolute thresholds to get upper bounds and lower bounds. This solves the problem of loose thresholding in relative thresholds and strict thresholds of the absolute thresholds.

The system also allows editing of the sketched diagrams - delete, scale, drag ...

Discussion:
I see no significance in recognizing the letters inside the node. As they are just symbols to recognize each node , should it be recognized? Is it not enough to recognize just the nodes , lines and the constraints?. Removing letters from the recognition ,can actually reduce the complexity of rules.