The development and implementation of an algorithm for automated text string separation that is relatively independent of changes in text font style and size and of string orientation are described. It is intended for use in an automated system for document analysis. The principal parts of the algorithm are the generation of connected components and the application of the Hough transform in order to group components into logical character strings that can then be separated from the graphics. The algorithm outputs two images, one containing text strings and the other graphics. These images can then be processed by suitable character recognition and graphics recognition systems. The performance of the algorithm, both in terms of its effectiveness and computational efficiency, was evaluated using several test images and showed superior performance compared to other techniques. >

A robust algorithm for text string separation from mixed text/graphics images

A system for interpretation of images of paper-based line drawings is described. Since a typical drawing contains both text strings and graphics, an algorithm has been developed to locate and separate text strings of various font sizes, styles, and orientations. This is accomplished by applying the Hough transform to the centroids of connected components in the image. The graphics in the segmented image are processed to represent thin entities by their core-lines and thick objects by their boundaries. The core-lines and boundaries are segmented into straight line segments and curved lines. The line segments and their interconnections are analyzed to locate minimum redundancy loops which are adequate to generate a succinct description of the graphics. Such a description includes the location and attributes of simple polygonal shapes, circles, and interconnecting lines, and a description of the spatial relationships and occlusions among them. Hatching and filling patterns are also identified. The performance of the system is evaluated using several test images, and the results are presented. The superiority of these algorithms in generating meaningful interpretations of graphics, compared to conventional data compression schemes, is clear from these results. >

A system for interpretation of line drawings

A methodology for the interpretation of images of engineering drawings is presented. The approach is based on the combination of schemata describing prototypical drawing constructs with a library of low-level image analysis routines and a set of explicit control rules applied by an LR(1) parser. The resulting system (Anon) integrates bottom-up and top-down processing strategies within a single, flexible framework modeled on the human perceptual cycle. Anon's structure and operation are described and discussed, and examples of its interpretation of real mechanical drawings are shown. >

Knowledge-directed interpretation of mechanical engineering drawings

A system for the automatic acquisition of land register maps is described. The system converts paper-based documents into digital form for integration into an existing database. Processing a map begins with its digitization by a scanning device. A key step in the system is the conversion from raster format to graph representation, a special binary image format suitable for processing line structures. Subsequent steps include vectorization of the line structures and recognition of the symbols interspersed in the drawing. The system requires operator interaction only to resolve ambiguities and correct errors in the automatic processes. The final result is a set of descriptors for all detected map entities, which is then stored in a database. It is shown that the image representation, vectorization techniques, and optical character recognition subsystem are quite general and that the methodology implemented in the system can be generalized to the acquisition of other classes of line drawings. >

An interpretation system for land register maps

One of the most fundamental questions in visual language research is how to specify a visual language. By a visual language we mean a set of diagrams which are valid “sentences” in that language where a diagram is a collection of “symbols” in a two or three dimensional space. Which sentences are valid and what their meaning is depends on spatial relationships between the symbols. Thus, for example, mathematical expressions, plans, and musical notation are commonly used visual languages. In this chapter we survey the many formalisms which have been suggested over the last three decades for visual language specification, and also indicate their possible applications.

A survey of visual language specification and recognition

A Canadian feasibility study shows that the key to reliable and cost-effective automatic reading of drawings is detailed planning of an operator-assisted system.

Tim O. McNeil

Papers

From Paper Drawings to Computer-Aided Design

From paper drawings to computer-aided design