Boundary Labeling with Octilinear Leaders

A major factor affecting the readability of an illustration that contains textual labels is the degree to which the labels obscure graphical features of the illustration as a result of spatial overlaps. Boundary labeling addresses this problem by attaching the labels to the boundary of a rectangle that contains all features. Then, each feature should be connected to its associated label through a polygonal line, called leader, such that no two leaders intersect. In this paper we study the boundary labeling problem along a new line of research, according to which different pairs of type leaders (i.e. doand pd, odand pd) are combined to produce boundary labelings. Thus, we are able to overcome the problem that there might be no feasible solution when labels are placed on different sides and only one type of leaders is allowed. Our main contribution is a new algorithm for solving the total leader length minimization problem (i.e., the problem of finding a crossing free boundary labeling, such that the total leader length is minimized) assuming labels of uniform size. We also present an NP-completeness result for the case where the labels are of arbitrary size.

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