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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
I. To one part in the set, assume one of its nodes, P,, which 
is not at map boundary. The distances of P, to the two 
neighbor contour lines are d, and d». Compute the ratio r 
of d, to d. 
2. Geta triangle, if there is, one of whose vertices are P, and 
the other two are from the involved two neighbor contour 
lines. Interpolate a point on the facing edge of P, by the 
ratio got above. Insert the interpolated point in the broken 
part and CDT and let it be a new start. If there is not a 
triangle with that property then the interpolation reaches 
the map boundary or another broken part which joins 
current part to one. 
3. Repeat above until the current set is connected into one 
contour line. 
4. Repeat above until there is not broken part. 
In figure 7(a) there are two broken parts of one contour line and 
interpolation is started at P,. Triangle P,P,P; that is formed by 
three linking edges and involved three objects is used to 
interpolate a new point on edge P)P;. The thin solid line is 
interpolated to connect the two broken parts in figure 7(b). 
5. CONCLUSION AND DISCUSSION 
This paper designs a novel formalization framework of 
topological relation of contour lines based on the continuity of 
proximal relation between contour lines and the direction of 
contour lines. It is more practical because it only need to 
consider the adjacent contour lines. The algorithm implemented 
to construct the relation is more robust and efficient than raster 
algorithm and previous vector ones for it integrates the situation 
that there are often broken contour lines in topographic maps. 
We believe there are other interesting applications of this 
formalization framework than automatic contour labelling and 
the connection of broken contour lines in CDT as derivation of 
terrain features and terrain classification. Further research can 
consider the geometric characteristics of contour lines for these 
I-d curves implicate some characteristics of the 3-d topography 
and it may be of benefit to find the situation of local pits in the 
automatic contour labelling process and design more flexible 
algorithm for connecting the broken parts of contour lines at 
more complex situations. 
ACKNOWLEDGEMENT 
The suggestions and encouragements of Professor Hehai Wu 
and Professor Tinghua Ai at Wuhan University are gratefully 
acknowledged. 
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