I need help with finding information on writing voxel landscape engine with 6 degrees of freedom. I''ll be happy about all online information resources. Thank you

A site from someone considering doing the same thing :
http://www.base-sixteen.com/terraVox/

Two papers on extending the basic "voxel" method to 6 DOF :
http://citeseer.nj.nec.com/28271.html
http://graphics.lcs.mit.edu/~gs/research/dispmap/
(they describe the same method, but with different words and different applications ... I am not aware of any available implementation of the algorithm BTW)

These papers describe the only real way to extend the "voxel" method to 6 DOF, you can use a 4 DOF "voxel" engine and use image shearing/warping to simulate 6 DOF ... but it looks like crap. In theory you could also just raycast the heightmap without using ray coherence, read the first paper to understand what I mean there, but its just too damn slow.

For a hardware accelerated engine you are better off with a CLOD approach BTW (although that leaves the task of performing occlusion culling, which in a "voxel"-engine is built into the same algorithm). For some doc''s on that topic and on examples of landscape engines in general see :
http://ddg.sourceforge.net/telist.html

1) Make rough frustrum and occlusion culling in a lowres 4DOF software engine,
2) render all visible clusters as hw accel''d polygon meshes.

A cluster has the size of one voxel, and can be for example
flat street, grass with tree on it, corner of a house, I mean like
in 2D tile-based games.

Meshes of this size can be rendered very fast on todays hardware.
Triangle counts are so high nowadys, that it does not have to look edgy.
You can yous LOD for your clusters. With these hight triangle counts,
popping is less noticeable.

Arne