Thanks, I got the same info from another newsgroup and it worked great.

Here's the catch:  I've been using POV since version 0.5.  A long time ago I
started writing C/C++ programs to generate POV scripts and I still do.  The
fact of the matter is that what I used to need C/C++ for can now be done in
POV.  I should really just port my program to a POV script, but for now it's
just easier to keep doing what I'm doing.

Thanks,

Rick



"Ken Cecka" <cec### [at] alumniwashingtonedu> wrote in message
news:39C04B05.969385E2@alumni.washington.edu...
> First let me rephrase your question:
>
> You have a generic branch aimed in a particular direction.  You want to
> automatically reorient it to match branches on your tree.  The actual
> position of the branches doesn't really enter into the picture here
> because that is just translation, so we can simplify the problem to
> changing the orientation.  Now, lets say your generic branch starts at
> the origin, and ends at the point <Ax,Ay,Az>.  And you want to re-orient
> it so that it ends at <Bx,By,Bz>.  Lets refer to these points as
> vectors, A and B, and make one more simplification, that A and B are the
> same length.
>
> If this sounds like it describes what you want to do, it's the same
> question I asked several years back, and John VanSickle provided a great
> solution using Pov's generic matrix transforms.  He describes it on his
> web page on matrices at
>
> http://users.erols.com/vansickl/matrix.htm
> (scroll down to the section titled "Rotating from one vector to
> another")
>
> I never muddled through it enought to understand the math behind it, but
> it worked great for me at the time.
>
> Hope that helps (credit goes to John),
>
> Ken
>
> Rick Gutleber wrote:
> >
> > I've got a simple question that's bugged me for years.  The answers got
to
> > be simple, but I just can't figure it out.
> >
> > I'm writing a C++ program to programmatically generate a Christmas tree
and
> > I'm trying to put needles on the branches.  I have the start and end
point
> > of the branch so I figured I would create the needles as if the branch
> > started at the origin and pointed straight up and then just translate
and
> > rotate the union of the resulting needles so they actually appear on the
> > branch in the scene.  This translatation/rotation can occur in my C++
code
> > or the generated POV script, whichever is easier.
> >
> > I've got an arbitary unit vector that reflects the orientation of the
branch
> > (from VNormalize( ) in POV, or the good old Pythagorean distance
function in
> > my C++ code), how do I turn that into an equivalent rotate < x, y, z >
> > statement so the needles end up on the branch?  I'm sure it's just the
right
> > combination of atan( ) calls, but the details elude my addled brain.
> >
> > Thanks for the help!
> >
> > Rick
> > ric### [at] hiscom

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