Plan oblique relief for web maps

Abstract

Plan oblique relief shows terrain with a side view on a two-dimensional map, resulting in visualizations where the third dimension of the terrain is more explicit than on traditional two-dimensional maps. Existing plan oblique maps are static: the angle of terrain inclination is not adjustable and the orientation of plan oblique inclination does not change with the orientation of the map. This article introduces two complementary methods that address these issues by using the 3D graphics pipeline to render plan oblique relief for tile-based web maps. The goal is to allow users to adjust the terrain inclination and map rotation angles to better visualize the third dimension of the terrain. The first method pre-renders plan oblique tiles with a server-side application. The tiles are visualized with a standard web mapping framework. The second method renders plan oblique relief on-the-fly in a web browser using WebGL and a customized version of OpenLayers 3, which enables users to select arbitrary terrain inclination and map rotation angles. The second method uses a tiled digital terrain model that is loaded by the web browser. The browser applies the plan oblique transformation, computes a shaded relief, and texturizes the terrain with tiled map layers.

Keywords:

• plan oblique relief
• 3D map
• relief map
• terrain map
• WebGL
• OpenLayers 3

Acknowledgments

The authors would like to thank William McNulty of Google for his support and Google for a Faculty Research Award. The authors would like to give special thanks to Brooke E. Marston, Oregon State University, for editing the text of this article, to Tom Patterson and Roger Smith for the permission to reproduce their maps, and to the anonymous reviewers for their valuable comments.

Additional information

Funding

This work was supported by the French National Research Agency [grant number ANR-12-CORD-0025] and Google through a Google Faculty Research Award.