Subject:
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Re: Finding a rotation matrix for a triangle
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Newsgroups:
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lugnet.cad
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Date:
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Mon, 28 Nov 2005 18:55:53 GMT
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Viewed:
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1405 times
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Niels Bugge wrote:
> Back in the math class years ago, one of the possible definitions of
> a plane was a vector starting in some point on the plane, standing
> out at a 90 degrees angle to it. That way you would know the 3d angle
> of the plane from the vector.¬
> Now, if I could get the 3d rotations of such a vector corresponding
> to my triangle, I would be able to place any primitive precisely on
> it at the right angle.
You take the cross product of two of the sides of the triangle, this will
give the vector perpendicular to the triangle plane:
http://mathworld.wolfram.com/CrossProduct.html
It will point either upwars or downwards. Unless your triangle is in a known
winding state there's no way to programmatically decide what's up or down.
--
Anders Isaksson, Sweden
BlockCAD: http://web.telia.com/~u16122508/proglego.htm
Gallery: http://web.telia.com/~u16122508/gallery/index.htm
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Message has 1 Reply:
Message is in Reply To:
 | | Re: Finding a rotation matrix for a triangle
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| What I mean is: In MLCad, you can take a part, and rotate it via a vector command like turn 45 degrees around y axis clockwise. Or more complex rotations based on more axes. What I would like to know is: How do I find the rotation vector of a plane (...) (19 years ago, 28-Nov-05, to lugnet.cad)
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