A new method of three-dimensional orientation chain coding for recognition and plotting

A new method for 3-D space curve encoding is presented. The new method, "orientation chain coding", uses the orientation angles as the quantization criteria for encoding a local curve segment. The space curve can be chain coded by tracing either the source curve or the decoded curve. The source curve chain coding procedure preserves the pattern of changing curvature by encoding each original curve segment directly. The resultant code string preserves the global curve shape. This is an essential property in recognition oriented tasks.;Given an arbitrarily shaped surface patch, a mesh description made of space curves lying on the surface can be used to represent the surface. Since the curve shape is preserved during the encoding procedure, the resultant code strings of the curves lying on the surface can be used to represent the shape of a surface patch. For surfaces with regularity, the curve patterns lying on them also exhibit regularity. The encoding method for preserving curvature can be used to derive a structural surface representation, and the curvature changes of the curves can be used as features for surface shape recognition. The curve patterns on quadric surfaces are discussed.;This source curve chain coding method can also be used to represent the 3-D trajectories of characteristic points on moving objects. Since the shape of a trajectory is preserved, the code string can retain the features of a time varying movement and thereby, can be used for motion understanding and tracking.;When the global quantization error is the major concern in encoding a curve, the approximated orientation chain coding can be used. This method encodes a curve based upon the decoded curve. At each encoding step, a code that can minimize the global quantization error of the decoded curve is selected. The resultant code string can precisely approximate a space curve. A set of such code strings, therefore, can precisely approximate an arbitrarily shaped 3-D surface patch.