Global visualization process terrain database builder

1. A process for prioritized refinement of a tile mesh modeling a surface in a level-of-detail hierarchy, comprising:

obtaining a plurality of elevation values for an elevation grid of the surface;

downsampling a rasterized elevation grid to a resolution based on a minimum edge size for triangles of the tile mesh, as determined by a level-of-detail (LOD) parameter, balancing object-space and view-space LOD mechanisms;

encoding the elevation grid into a linearized quadtree of virtual nodes;

iteratively refining the quadtree according to an adaptive sampling pattern based on prioritized split tests using application specific criteria; and

converting the optimized linearized quadtree into a tile mesh,

wherein a split test forces a limiting degree of prioritized refinement along mesh boundaries in multi-tile databases to avoid introducing inter-tile data dependencies during tile creation and display.

2. The process according to claim 1 , wherein the prioritized split tests comprise a constraint on a degree of refinement along mesh boundaries so as to ensure avoidance of artifacts.

3. The process according to claim 1 wherein the prioritized split tests comprise a smoothness test, to ensure that the tile mesh adequately approximates the curvature of a planetary body when warped into a geocentric coordinate space, irrespective of any surface features that may or may not be present.

4. The process according to claim 1 , wherein the prioritized split tests comprise a maximum sampling error test.

5. The process according to claim 1 , wherein the prioritized split tests comprise a polar-sampling test that constrains the refinement of the mesh at extreme latitudes to compensate for singularities at the poles caused by geographic projection.

6. The process according to claim 1 further comprising using a dynamic, weighted combination of vertex normals and normal maps to enhance the appearance of surface topography and facilitate transitions throughout the level-of-detail hierarchy.

7. The process according to claim 1 wherein smooth transitions between coextensive tile meshes at adjacent levels of detail are supported.

8. The process according to claim 1 wherein the smooth transitions between coextensive tile meshes at adjacent levels of detail are supported using hardware acceleration.

9. The process according to claim 1 wherein terrain shaders may be optionally registered with a tile data structure comprising the tile mesh.

10. The process according to claim 1 wherein the level-of-detail hierarchy may exceed a client computer's memory.

11. The process according to claim 1 wherein the tile mesh produced is suitable for use in both flat-earth and round earth terrain model databases.

12. The process according to claim 1 , wherein a split test enforces a maximum sampling error and applies to a single or multi-tile database assuming either a flat or ellipsoidal reference model.

13. The process according to claim 1 , wherein a split test ensures that the tile mesh approximates the curvature of a planetary body when warped into a geocentric coordinate space, irrespective of any surface features that may or may not be present.

14. The process according to claim 1 , wherein a split test is a polar sampling test that constrains the prioritized refinement at extreme latitudes to compensate for singularities at the poles caused by geographic projection.

15. The process according to claim 1 , wherein the tile mesh is suitable for use with point-of-interest terrain models where priority is allocated to specific locations on the terrain.