Re: Fortran to find nearest point from set in 3-D

octree I know about, but k-d tree etc. are new to me. By the way, I
will have to do this 'proximal-point' problem hundreds of times with
different sets of points B.

MOST of B can be eliminated at a glance. ... "At a glance" requires more computational effort than glancing

I figure that, too.

presumably you're already computed the distances from the grid cubes to
the old point ... discrete approximation to a convex set

Huh?

Do you know anything more about the sets?

Yes. Set A (the small one) comes from the triangular discretisation on
a set of surfaces and Set B (the big one) comes from the the corners of
a tetrahedral discretisation of 3-D space. Unfortunately all the
connectivity has been lost in the form that I have access to.

This means that the points in B are roughly equidistance apart, I may
even be able to give an 'a priori' maximum distance apart. If it helps,
call it 'D' for distance. I can also put hard upper and lower bounds on
each of the x, y and z of the triples (x,y,z) in B.

And if it's good enough to do this in the sup (max) norm instead of the
L^2 norm

L^2 won't take that much more time provided I remember not to take
square roots :-)

.