An Incremental Parser to Recognize Diagram Symbols and Gestures Represented by Adjacency Grammars

Syntactic approaches on structural symbol recognition are characterized by defining symbols using a grammar. Following the grammar productions a parser is constructed to recognize symbols: given an input, the parser detects whether it belongs to the language generated by the grammar, recognizing the symbol, or not. In this paper, we describe a parsing methodology to recognize a set of symbols represented by an adjacency grammar. An adjacency grammar is a grammar that describes a symbol in terms of the primitives that form it and the relations among these primitives. These relations are called constraints, which are validated using a defined cost function. The cost function approximates the distortion degree associated to the constraint. When a symbol has been recognized the cost associated to the symbol is like a similarity value. The evaluation of the method has been realized from a qualitative point of view, asking some users to draw some sketches. From a quantitative point of view a benchmarking database of sketched symbols has been used.