Labeling Streets in Interactive Maps Using Embedded Labels

Abstract

We consider the problem of labeling linear objects (such as streets) in interactive maps where the user can pan, zoom, and rotate continuously. Our labels contain text (such as street names). They are embedded into the objects they label, i.e., they follow the curvature of the objects, they do not move with respect to the map background, but they scale in order to maintain constant size on the screen. To the best of our knowledge, this is the first work that deals with curved labels in interactive maps.

Our objective is to label as many streets as possible and to select label positions of high quality while forbidding labels to overlap at street crossings. We present a simple but effective algorithm that takes curvature and crossings into account and produces aesthetical labelings. On average over all interaction types, our implementation reaches interactive frame rates of more than 85 frames per second.

Video

We have implemented our algorithm. For our tests, we extracted a map of our hometown Würzburg from an OpenStreetMap data set that is provided by GEOFABRIK. The set contains 620 polylines.
Moreover, we have implemented some camera paths. In the following two videos, we show a camera path where all types of interaction (panning, zooming in, zooming out, rotation) are executed. We only show a quite small part of the map as we intend to simulate a navigation system.

The first video gives an impression of how our heuristic works. It shows a larger part of the map than a navigation system would. The extension of the virtual display is indicated by a brighter rectangle. The video shows the interactions in slow motion. With these two tricks, we enable the viewer to better understand the behavior of our algorithm.


If the video does not work, you can download it (39 MB, DivX-compressed).

Some comments:

• Sometimes labels overlap a little bit.
  This is due to the fact that we use an outline (black border around characters) that visually enlarges the label.
• While rotating, labels flicker; for example, Silcherstraße at 2:55 to 3:00.
  For determining street segments that lie within the view, we test if the start or the end point of a segment lies within the view. Indeed, there are segments that start and end outside the view but yet intersects it.
• Characters of a label overlap.
  As there are renderer for OpenStreetMap data for placing letters of curved text, we did not pay too much time for our drawing routine.

The second video reflects a natural speed of interaction; it shows only the virtual display (e.g., of a navigation system).


If the video does not work, you can download it (24 MB, DivX-compressed).

→ The labelings of the two videos might differ a little. As the speed of the movement differs, the number of visible segments of a street differs and, in turn, the evaluation differs.

The third video shows the same camera path as before but in a bird view. Our labels have a perspective distortion.


If the video does not work, you can download it (48 MB).

Acknowledgments

Combination of Two Street-Labeling Algorithms: Embedded Street and Billboard Labeling

When using a digital map in navigation mode, labels along a user's route are very important for the user. Consequently, these labels should be very well legible. On that account, for her PhD thesis (download), Nadine Schwartges also combined the algorithm for embedding curved labels into their streets and the algorithm for labeling streets along a route with billboards. For the following video, we use the same map as before.


If the video does not work, you can download it (24 MB).