"K. Seshadri" wrote:
>> Mark wrote:
>> > Given the cartesian coordinates of
> > two points a and b in 3D space, I need the position
> > of a third point c such that the angle c-a-b has a fixed
> > value, say 104.5 degrees.
> > c
> > \
> > a - b
> > how can I obtain the coordinates (x,y,z) of c from the
> > known coordinates of a and b?
> > Clearly there are many equivalent choices of c satisfying
> > this requirement; what I'm looking for is simply the direction of some
> > a-c axis which form the required angle with the a-b axis.
> > is it a trivial problem? I haven't found a solution...
> > any help appreciated
> > Sent via Deja.com http://www.deja.com/> > Before you buy.
> The direction of a-c vector itself is not unique given the angle at a.
> It will sweep a cone about the axiz a-b. You need to provide atleast
> one more constraint in order to have it fixed.
Juma, Mark wants the equation for a cone at "his" angle to a - b, with
the apex of the cone at a. There should be an unequivocal equation for
that, but I'm not a good enough math person for that.
(Please answer to the newsgroup)