You don't understand!  The answer I wanted was something like "that's easy -
use VrotateLikeMarkWants()"

I'll have to try and work out a "manual" approach :(  trig here I come...
--

Mark Hanford
http://www.mrhanford.com/povray


"bob h" <omn### [at] charternet> wrote in message
news:3ca48bd9$1@news.povray.org...
> "Mark Hanford" <ren### [at] blueyondercouk> wrote in message
> news:3ca4518f@news.povray.org...
> >
> > I have an object created at the origin and oriented along the x-axis (an
> > arrow, actually).
> > What I want to do is rotate the arrow to point in a particular
direction,
> as
> > specified by a vector.
> >
> > So for a vector of <3,3,0>, the rotation should be <0,0,45>
>
> Well, there is vaxis_rotate and vrotate but those result in a vector
> position, not the rotational amount between two vectors. I'm no math
wizard
> to begin with so I'm not sure if there is an easy way. In the beta of 3.5
> (3.1 and 3.5 are going to be quite different regarding this I believe) a
> math 'include' macro might do okay. One is VAngleD, which can result in
the
> number of degrees between two vectors. Might be a problem if you wanted it
> to give you the axis of rotation, but another macro called VRotationD will
> give you the degrees rotated based on what you specify as the rotational
> axis. See my example of that, if you have version 3.5:
>
> #include "math.inc"
>
> #declare Angle=VRotationD(x, <3,3,0>, z);
>
> text {ttf "timrom.ttf", str(Angle,0,0), 1, 0
>         pigment {color red 1}
> }
>
> Note that I used "x" for the first vector (same as <1,0,0>) because the
> macro can't see <0,0,0> in a way that can figure it out apparently. So
you'd
> think of the first as a starting plane, I guess that's a good way to
explain
> it. If the vectors are non-zero then the macro can calculate against those
> as planes, from what I can tell. Also, sign (+/-) is based on a different
> geometry from the left-handedness rotation, it would seem. Frankly, I'm
not
> certain how it is done and what results should be expected.
> Perhaps someone else could give you a better idea.
>
> bob h
>
>
>

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