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Perpendicular and Parallel



Hi,
I have to find the vector "pv" perpendicular to an arbitrary vector "tv".
The perpendicular vector "pv" has to be parallel to the XZ (floor) plane.
How to do it?

I have successfully found a generic perpendicular with the cross product
between tv and a random vector rv. Of course the result is a vector not
always laying on the XZ plane so pv[1] != 0.
So I have found this trick. Firstly I set rv = tv. Then I set rv[1] = 0 or
rv[1] += 12345; So tv and pv lay on the same vertical plane.
So I find pv[1], that is pv is parallel to the plane XZ. Good.
The problem is that this trick doesn't work for any tv. E.g. when tv is
{0, 1, 0} it doesn't work.


Best Regards
-- 
Lorenzo
email: email@hidden

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