Ellipsoidal Clipmaps – A planet-sized terrain rendering algorithm

Abstract

Terrain visualization is an important aspect of many applications, especially of 3D geographic information systems, which try to preserve the accuracy of the applied terrain model. A discrepancy of data representation, efficient streaming and the application to a chosen mathematical model of the whole planet, still imposes a challenge to a number of large terrain rendering engines. In this paper, we present ellipsoidal clipmaps – a new way to apply geometry clipmaps to an ellipsoid. The ellipsoid is divided into three partitions, seamlessly stitched together. Unlike previous geometry clipmap approaches, based on preloaded grid upon which the terrain is elevated, the underlying ellipsoidal grid is generated on the fly in the vertex shader. The proposed method guarantees sub-pixel precision of the planet Earth reference ellipsoid surface calculation, exploiting GPU single precision floating-point arithmetic. A tight coupling with the implementation of clipmaps enables consistent caching and fast data streaming, while the usage of equidistant cylindrical projection for the source data minimizes preprocessing and preserves low-to-moderate texture distortion.