[vtkusers] Speed up strategies for ray casting using vtkOBBTree?

[BBerco]

Dear all, 
I'm working on some ray casting applications with the help of vtkOBBTree.
This class does a fine job as it is easy to use and does exactly what I
want, but I was wondering if I could speed up the ray-casting process when
large data sets are involved.

I am dealing with ray-tracing from a LIDAR focal plane comprised of 128 x
128 elements to a target potentially comprised of hundreds of thousands of
vertices (833538 in my example). Illuminating it with each of the 128 x 128
= 16384 pixels in the focal plane takes more than 15 minutes (as my timer is
still running!). Obviously this is a computationally intensive problem, but
I was wondering if there were some alternative strategies that could speed
up the process.

Specifically, because I am casting each ray by going through the focal plane
rows by rows, the facet hit by the ray corresponding to pixel [i,j] should
be pretty close  to the facet hit by the ray coming from pixel[i,j+1] (if
not the same). So here's my first question: is their a way to restrict the
ray-facet intersect search to the neighbors of a given facet? This way, only
the very first pixel of the focal plane would require a global search
through the vtkOBBTree: the rest of the intersects could be searched inside
the neighbors of the impacted cells (and not inside the complete shape).

I guess I could somehow implement manually, but i'd rather not reinvent the
wheel.

Besides this idea, if there any ray casting strategy using built-in VTK
features more adapted to large datasets such as those I am dealing with?

Thanks!

Ben










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