In article <3ee52eb6@news.povray.org>,
 Lutz-Peter Hooge <lpv### [at] gmxde> wrote:

> Christopher James Huff <cja### [at] earthlinknet> wrote:
> 
> > What were the render times like?
> 
> For 512x384 without AA:
> 
> bilinear:               14s
> bilinear as function: 1m05s
> bicubic as function:  4m10s
> 
> So bicubic is about 4 times slower (not unexpected, it uses 16 samples
> instead of 4 in bilinear).

I was actually wondering about isosurface vs. height field.
An isosurface solver optimized for the constraints of a height field 
might be worth it...I've done some experiments with this before in my 
little test-bed tracer, I might revive that work. With an image as the 
data source, it could do some things to further speed computation.

For example, I'm thinking about a quad-tree structure storing the min 
and max heights of areas to allow them to be skipped in the intersection 
search. (If a ray enters and exits a partition above or below the range 
of the height field, an intersection is not possible.) This optimization 
should also be possible for mesh-based height fields, but I suspect 
wouldn't be much of an improvement over a more straightforward quad-tree 
method.

There are a few other improvements that could be made to the existing 
primitive. At least one thing which has already been done by someone 
else: switch the orientation of the two-triangle patches depending on 
the direction the surface is curving. This way, the diagonals follow the 
contours of the curves and the artifacts are much less jarring. Better 
smoothing would also be nice, I find it hard to believe the current 
smoothing is optimal. And a couple more ideas...I kind of like the 
bilinear patch effect of the isosurface, and am going to try to figure 
out how to test intersections directly. And there's a point-cloud 
raytracing algorithm that I've been looking at which might work nicely 
on height field data.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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