Expert: Sherman D. - 1/6/2008

Question
I am doing some physics programming, and I need to be able to generate a
circle of 3d points around a given center point on a given plane.  So if I
randomly made a plane in 3d space, I could generate a given number of
points around a given point on the plane (in global coords) with a given
radius.

given:

The plane is defined by an normal vector and scalar value 'k'.
Vectors are all x,y,z and basic vector math can be performed
(project,cross,etc)

what i've tried:

I made a group of 2d points that are in a circle, and tried to project that onto
the planes, but I ended up with ellipses (which makes sense if you think
about it).

I know that somehow you could rotate and transform the 2d points (if they all
has z=0) to go onto the plane, but i'm not sure how to do this.  I can use
matrices and basic matrix function (translate, scale rotate), and rotation is by
giving angle(degrees) and then the vector to rotate around.

I am completely stuck on this any help would be greatly appreciated.  

Answer
www.algebrahelp.com/calculators

click on 3D Equation Graphing Calculator.

for a 3D, you have to take in x, y, and z form. if you are working with 2d points, then you have (x,y), (x,z), and (y,z), i'm guessing your only using (x,y) type coordinates.

keep in mind that the circle cordinates are

(x - h)^2 + (y - k)^2 = r^2

you might need to be thinking spherically.

Other than this, sorry i can't help you, because i don't work in 3D.

except when trying to find solutions to

ax + bx + cz = d

type problems where you have workable rows and columns. And i don't use matrices to solve them.