Conclusions
The simulation of wood grain using solid texturing is not
easy. Between adding noise and turbulance there are many parameters
that need to be tuned before a reasonable model is achieved.
While the base model of concentric cylinders and the use of
cylindrical coordinates makes for a nice intuitive mapping to logs in
the real world. This model can yield poor results if the object is
allowed to be placed at large distances from the z-axis. This is
because as R increases the arc swept out be theta increases causing
effects such as birdseye to enlarge and blur.
Lastly as pointed out in [1] and evident from the model of birdseye,
realistic models of woods(especially figured woods) are dependent on
more than just the x, y, z coordinate. In addition to surface normals,
the vectors from the point to the light source and to the viewer would
be needed to capture the irredesence of many woods.