[vtkusers] another question!- the order of three arbitrary points

[Andrew Maclean]

I think that you can just use the cross-product on the vector p1-p2 = V1 and
the vector p1-p3 = V2. Then V1 X V2 will give you the direction of the
normal. If this normal is in the direction you want than p1,p3,p2 are in
anticlockwise order. However if V2 X V1 gives you the normal in the
direction you want then p2,p3,p1 is the order you want. You can verify this
with a sheet of paper.

I guess the point is you have to decide what is outside, make sure the
normal points in that direction and then the ordering of the points follows
the scheme above.


Hope this helps,
   Andrew





1/07, PAUL <polinzhuo at 163.com> wrote:

>  Hello, everyone,
>
> As we know, we can get the exact direction of a plane, through the order
> of three arbitrary points on the plane, according to the right –hand rule.
> But I don't know how to find a way of getting the anticlockwise order of
> three arbitrary points when I watch an object from outside.(The three
> arbitrary points are on the object.)
>
> Paul
>
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-- 

___________________________________________
Andrew J. P. Maclean
Centre for Autonomous Systems
The Rose Street Building J04
The University of Sydney  2006  NSW
AUSTRALIA
Ph: +61 2 9351 3283
Fax: +61 2 9351 7474
URL: http://www.cas.edu.au/
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