Hexagonal Geometry Clipmaps for Spherical Terrain Rendering

Terrains can be rendered efficiently with rectangular 2D grid of heights. Terrain on spheres, on the other hand, can be rendered using Hierarchical Triangular Mesh (HTM) but the representation does not fit directly with 2D grid of heights. We present a unified representation of HTM and clipmapping using Hexagonal Geometry Clipmaps. This provides one to one correspondence of vertices and heights, low and constant memory usage, less storage space requirements, no pole singularity, fast vertex look-ups, and large range of view distances. Hexagonal clipmaps fit equilateral triangles of HTM and achieve uniform triangle count on the screen. We keep the clipmaps on the GPU for fast access from shaders and use vertex buffer objects for fast triangle rendering.