Recognition of hand-lettered characters in the GTX 5000 drawing processor

The GTX 5000 drawing processor is a commercial device that scans engineering drawings and converts them to computer-aided design format. As part of this process, it automatically classifies the hand-lettered (or occasionally machine-printed) characters that appear on the drawing. The techniques used in this process are described. Although the basic approach (decision trees using numerical features) is standard, the nonparametric recursive technique described for building the decision trees and the use of multiple decision trees for confidence determination are useful refinements. The author also discusses many of the requirements and practical engineering consideration needed to make this commercial product. Finally, results are given on the accuracy of the character-recognition system, based on a set of approximately 9000 hand-lettered characters from engineering drawings