As is well known, the contour line has always been the key unit in such projects of automatic recognition of geographic
maps, but how to handle the contour lines' breakpoints automatically is still not settled thoroughly. This paper first
synthetically analyzes four classical algorithms of the contour lines' breakpoints connecting methods, then presents a
layering-based breakpoints connecting policy. Taking brown plate map as data source, separately recognizing and
extracting the influencing factors such as elevation annotation, dry riverbeds, cliffs symbols which lead to the contour
lines' long-distance break from the map as the reference layers, then judging on the reference layer when connecting the
breakpoints, and according to the different influencing factors, designing the corresponding algorithms to achieve the
true connecting of the contour lines.
This paper first synthetically analyzes three classical algorithms of constructing Delaunay Triangulation Irregular Net (DTIN),
then uses improved convex hull algorithm to construct non-constrained D-TIN. The non-constrained D-TIN may
cause some Delaunay triangles which span contour lines, so these Delaunay triangles must be dealt with. Then the local
adjusting algorithm based on diagonals changing of the impacted region is used to embed contour lines into D-TIN as
constrained segments and ultimately construct constrained D-TIN (CD-TIN). After constructing CD-TIN which supports
the spatial data mining, it is easy to compute normal vectors of Delaunay triangles in the CD-TIN, and then get their
gradient values. By means of the relationship of gradient values and terrain features, flats and mountain regions can be
distinguished from topographic map based on contour lines. Even the terrain features such as mountain peak can be also
recognized in the recognized mountain regions primarily by Flat-Triangle whose three vertexes have the same digital
elevation.
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