Labeling Streets Along a Route in Interactive 3D Maps Using Billboards

Abstract

We consider the problem of labeling linear objects, such as streets, in interactive 3D maps, where the user can continuously pan, zoom, and rotate a perspective view of the scene. We dynamically annotate streets that belong to a user’s route, assuming that the future course of the route, within the currently visible part of the map, is known or well predicted. We use billboards as annotations, that is, each label is a rectangle holding the annotation text, is oriented towards the user, placed at some distance above the midpoint of the street to be labeled, and connected to the point by a vertical line segment, the leader. Our goal is to maintain an overlap-free labeling that reacts to changes of the view in real time. To this end, we dynamically vary the lengths of the leaders. In order to achieve that labels move smoothly, we do not strictly forbid label–label overlaps. We present a force-directed algorithm that applies forces to labels to cause overlapping labels to repel each other, while keeping leaders as close to their desired length as possible. On real-world data, with a realistic number of labels, we obtain frame rates of more than 400 frames per second, while drastically reducing the total overlapped area per frame, compared to an algorithm with fixed leader lengths.