Fix the awful ImplicitConvolveImpl.SetImagePath

ImplicitDraw
DrawOrthographicOctree
will draw those cubes terminal cubes crossing the surface, optimized for interpress output
Recursively check:
Test cubes at highest level first, enter line segments into a big array
is there anything clever about this?

ImplicitSurface
Curvature
set point.kMin and point.kMax: minimum and maximum curvature vectors at point.
do this numerically by binary subdivision in a circle in the plane perp. to surface normal.
SegmentConverge
Suppose you get a third point within the segment of convergence.
If the three points are approx. collinear, then use regula falsi;
otherwise, assume the function is complex enough to warrant fitting the three
points with a quadratic and solving for its roots
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