This paper presents a method for classifying pen strokes in an on-line sketching system. The method, based on linear least squares fitting to a conic section equation, proposes using the conic equation’s natural classification property to help classify sketch strokes and identify lines, elliptic arcs, and corners composed of two lines with an optional fillet. The hyperbola form of the conic equation is used for corner detection. The proposed method has proven to be fast, suitable for real-time classification, and capable of tolerating noisy input, including cusps and spikes. The classification is obtained in o(n) time in a single path, where n is the number of sampled points. In addition, an improved adaptive method for clustering disconnected end-points is proposed. The notion of in-context analysis is discussed, and examples from a working implementation are given.

1.
Ullman
D. G.
,
Wood
S.
, and
Craig
D.
,
1990
, “
The Importance of Drawing in the Mechanical Design Process
,”
Computers & Graphics
, Vol.
14
, No.
2
, pp.
263
274
.
2.
Jenkins, D. L., and Martin, R. R., 1992, “Applying Constraints to Enforce User’s Intentions in Free-hand 2-D Sketches,” Intelligent Systems Engineering, Autumn, pp. 31–49.
3.
Kato, O., Iwase, H., Yoshida, M., and Tanahshi, J., 1982, “Interactive Hand-Drawn Diagram Input System,” Proc. IEEE Conference on Pattern Recognition and Image Processing (PRIP 82), Las Vegas, Nevada, pp. 544–549.
4.
Pavlidis, T., and Van Wyk, C. J., 1985, “An Automatic Beautifier for Drawings and Illustrations,” SIGGRAPH 85, Vol. 19, No. 3, pp. 225–234.
5.
Bengi
F.
, and
Ozguc
B.
,
1990
, “
Architectural Sketch Recognition
,”
Architectural Science Review
, Vol.
33
, pp.
3
16
.
6.
Eggli, L., Bru¨derlin, B. P., and Elber, G., 1995, “Sketching as a Solid Modeler Tool,” Third Symposium on Solid Modeling and Applications, ACM SIGGRAPH, pp. 313–321.
7.
Lipson
H.
, and
Shpitalni
M.
,
1995
, “
A New Interface for Conceptual Design Based on Object Reconstruction from a Single Freehand Sketch
,”
Annals of the CIRP
, Vol.
44
, No.
1
, pp.
133
136
.
8.
Lamb, D., and Bandopadhay, A., 1990, “Interpreting a 3D Object from a Rough 2D Line Drawing,” Proc First IEEE Conf on Visualization, 90, pp. 59–66.
9.
Marti
E.
,
Regomco´s
J.
,
Lo´pez-Krahe
J.
, and
Villanueva
J. J.
,
1993
, “
Hand Line Drawing Interpretation as Three Dimensional Object
,”
Signal Processing
, Vol.
32
, pp.
91
110
.
10.
Smith
R. W.
,
1987
, “
Computer Processing of line images: A Survey
,”
Pattern Recognition
, Vol.
20
, No.
1
, pp.
7
15
.
11.
Spur, G., and Jansen, H., 1984, “Automatic Recognition of Hand-drawn Contours for CAD Applications,” 16th CIRP Int. Seminar on Manufacturing Systems, pp. 63–72.
12.
Koo, J. C., and Fernandez, B., 1993, “Geometrical Error Correction Using Hierarchical/Hybrid Artificial Neural Systems,” IEEE International Conference on Neural Networks, pp. 232–237.
13.
Bookstein
F. L.
,
1979
, “
Fitting Conic Sections to Scattered Data
,”
Computer Graphics and Image Processing
, Vol.
9
, pp.
56
71
.
14.
Shpitalni
M.
, and
Lipson
H.
,
1995
, “
Identification of Faces in a 2D Line Drawing Projection of a Wireframe Object
,”
IEEE Transactions on Pattern Analysis and Machine Intelligence
, Vol.
18
, No.
10
, pp.
1000
1012
.
15.
Lipson
H.
, and
Shpitalni
M.
,
1996
Optimization-Based Reconstruction of a 3D Object From a Single Freehand Line Drawing
,”
Journal of Computer Aided Design
, Vol.
28
, No.
8
, pp.
651
663
.
16.
Nalwa, V. S., 1988, “Line-Drawing Interpretation: Straight Lines and Conic Sections,” IEEE Pattern Analysis and Machine Intelligence, Vol. 10, No. 4.
17.
Faux, I. D., and Pratt, M. J., 1981, Computational Geometry for Design and Manufacture, John Wiley.
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