The Psi-s Plot: a Useful Representation for Digital Cartographic Lines

The Psi-s plot represents the geometry of a line by determining Psi, the orientation angle or heading, at points along the line, and plotting that value against s, the cumulative curvilinear distance along the line. No matter how convoluted the line is, the Psi-s plot will be a single-valued function of s; it is much easier to parameterize such a single-valued function. Straight lines on the Psi-s plot represent either straight lines or arcs of circles in x-y space. The Psi-s representation can be used to characterize the shapes of irregular polygons. It also has been used in analyses of river meander planform, and in the automated detection of contour crenulations. The Psi-s plot should be valuable in the generalization of digital cartographic lines; it should have an advantage over standard methods for representing geographic lines which include substantial proportions of circular arcs or straight lines. Circular arcs and straight lines are common components of rivers, roads, and railroads. The technique would appear to have great potential for feature recognition and shape characterization of digital cartographic lines. Electronic mail (BITNET) addresses for authors: ONEILLMP@VTVM1, GEODMM@UBVMS