The visualization was performed for three main reasons:

a) verification of the implementation correctness
b) exploring the properties of already implemented spatial data structures
c) possible design of new types of spatial data structures for ray shooting

First, set of images visualizing simple scene called balls1.nff in NFF format
from SPD package.

 The visualization of BVH (bounding volume hierarchy):

The visualization of OCTREE:
(Remark: BSP tree with midpoint subdivision will result in this case
   in the same subdivision)

The visualization of KD-tree:

The visualization of Uniform Grid:

There are some images for more complex scenes from the application. The application
based on OpenGL allows the visualization of these structures in realtime.

Uniform Grid:

Perspective mode of visualization inside the scene:

Only portion of KD-tree of scene tetra in "tree" visualization mode:

Scene gears in "path" visualization mode:

Scene teapot in "levels" visualization mode:

Only one object from scene balls visualized in "object" mode:

Adaptive Grids (Klimaszewski and Sedeberg) for scene tree in "scene" mode:

Locating error in the implementation of "Hierarchy of Uniform Grids"
  (some objects are referenced in the cells, where they do not belong, but
   the objects only touch these cells).

The visualization of spatial incoherency of BVH for larger spatial region
of scene "tetra":