Similarly, an interior pixel is one in which all of its ¿-neighbors 
belong to the property set. The pixel connectivity map for an inte 
rior pixel may be tested for all d-bits being equal to 1. 
B7 
B6 
B5 
B4 
B3 
B2 
B1 
BO 
-- 
1 
-- 
1 
-- 
1 
-- 
1 
Furthermore, arc endpoints or contour folds can be recognized as 
contour pixels with only one neighbor and similarly, collapsing arcs 
are contour pixels with no interior pixels as neighbors (Figure 1, 
c and e) 
Cederberg (1979) uses a 3 x 3 neighborhood template to identify local 
maxima and minima pixels of a connected component in the generation 
of his raster scan chain code. A complete set of templates for 
detecting maxima and minima points in contours, arcs, and holes is 
presented in Table 1 (O'Connor, 1982). The templates for detecting 
a local minima are obtained by a 180° rotation of the maxima tem 
plates, which can be achieved by a four place logical shift operation 
of the 8-bit template. 
Component junctions or intersections can be detected by scanning the 
pixel connectivity maps for hole maximum and hole minimum pixels 
whose distance is not greater than the width of the object they 
represent. The junction point lies between these pixels. 
12 3 4 
1 
HOLE MINIMUM ^ 2 
3 
4 
Each of these characteristics is further illustrated in Figure 1. 
ENHANCED EDIT SEQUENCE 
As a means of illustrating the application of the previously described 
techniques, a sample edit sequence is presented in Figure 2a-e. This 
figure presents cased roads which contain a line gap and line over 
shoot to be edited (Figure 2a). The cartographic editing operations 
referenced in this sequence are defined as follows (Kolassa, 1982): 
Join. Connects and relabels components. 
Divide. Separates a labeled connected component into two 
separately labeled components without altering them spatially. 
Delete. Eliminates all members of a similarly labeled connected 
component. 
477