Labeling collinear sites

We consider a map labeling problem, where the sites to be labeled are restricted on a line L. This is quite common e.g. in schematized maps for road or subway networks. Each site s_i, is associated with an axis-parallel w_itimesh_i label l_i, which can be placed anywhere on the "boundary" of the input line L. The main task is to place the labels in distinct positions, so that they do not overlap and do not obscure the site set, and to connect each label with its associated site through a leader, such that no two leaders intersect. We propose several variations of this problem and we investigate their computational complexity under certain optimization criteria.