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"david sharp" <dav### [at] rcn com> wrote in message
news:3d7c04ec@news.povray.org...
> Trying to get POV 3.5 spline object to behave.
Looks like a decent start on a roller coaster. :)
--
light_source{0,1}#macro c(J,a)sphere{0,1pigment{rgb z}scale a translate J+O}
#end#macro B(R,V,O)c(0,4)intersection{c(V,R)difference{c(-z*4x+10)c(-z*4.1x+
10)c(0<7.5,45,5>)}}#end B(12,0z*25)B(8y*4<0,12,50>) // Batronyx ^"^
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"Ryan Mooney" <rdm### [at] earthlinknet> wrote
> Source... Or clues...??
Once you have the spline points, calculate the direction the spline curve
is heading at each point (its tangent) and call that 'forward', calculate
the
direction the spline curve is curving towards (from the rate of change of
the tangent) and call that 'left'. Do vcross(forward,left) and call that
'up'.
I just assume that the ribbon should always try to span the up direction.
(That is, the width of the ribbon should be perpendicular to the curvature).
Then make two spline curves; one moved 'up' from the original spline
and the other moved 'down' from the original. The 'ribbon' (or track, or
whatever) fills in the space between the up curve and the down curve.
I will work on the source to post.
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