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Topic: Intersection between two cones
Replies: 6   Last Post: Feb 7, 2013 4:36 AM

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Posts: 6
Registered: 4/16/12
Re: Intersection between two cones
Posted: Feb 7, 2013 2:52 AM
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"Bill Whiten" <> wrote in message <keteb4$gmc$>...
> "Doctor61" wrote in message <ket0to$214$>...
> > I have two 3d circles (centre coordiantes and radii) with their normals passing through origin. If you consider the origin to be the vertex of a right cone having the circle as the base, how can I determine if there is an intersection between these cones?
> if centre is x1,y1,z1 and radius r set d^2=x1^2+y1^2+z1^2
> Cone is intersection of spheres a^2 (d^2+r^2)=x^2+y^2+z^2 and
> a^2 r^2 = (a x1-x)^2+(a y1-y)^2+(a z1-z)^2
> Eliminate a to get equation of cone:
> x^2+y^2+z^2 = (r^2+d^2) (x1 x+y1 y+z1 z)^2/d^4
> (check this)
> Set x^2+y^2+z^2=1 and solve for points on two cones and this sphere.
> E.g. Solve linear equations (1= (r^2+d^2) (x1 x+y1 y+z1 z)^2/d^4 etc)
> for x and y then substitute into x^2+y^2+z^2=1 to get quadratic for z.
> Regards

Thanks Bill, but I do not get your method. You said "Cone is intersection of spheres a^2 (d^2+r^2)=x^2+y^2+z^2 and
> a^2 r^2 = (a x1-x)^2+(a y1-y)^2+(a z1-z)^2". But intersection of two spheres is a circle. Could you please elaborate a little?

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