Hi,

I need to sample data in space on the faces of a 3D cube.

Is there a parametric equation that approximates the square (in 2D) or the cube (3D) ?

Thanks a lot!

Benoit

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- Nov 15th 2010, 09:33 AMbenoixParametric equation of the square? (or the cube in 3D)
Hi,

I need to sample data in space on the faces of a 3D cube.

Is there a parametric equation that approximates the square (in 2D) or the cube (3D) ?

Thanks a lot!

Benoit - Nov 22nd 2010, 08:39 AMragnar
A parametric equation that describes a surface must have two parameters, call them $\displaystyle u$ and $\displaystyle v$. Suppose you want a plane that runs through a point $\displaystyle P_{0}$ which contains two nonparallel lines $\displaystyle l$ and $\displaystyle m$. (In the case of a square in the first quadrant of a Cartesian plane with a corner at the origin, your point will be anywhere in the square and the lines can be $\displaystyle y = x$ and $\displaystyle y = 2x$.) Suppose the equations of the lines are given as $\displaystyle a_{1}x + b_{1}y + c_{1}z = d_{1}$ and $\displaystyle a_{2}x + b_{2}y + c_{2}z = d_{2}$ for constants $\displaystyle a_{1}, a_{2}, b_{1}..., d_{2}$ and suppose the point's coordinates are $\displaystyle (x_{1}, y_{1}, z_{1})$. Then the parametric equations of the plane will be $\displaystyle x = x_{1} + ua_{1} + va_{2}, y = y_{1} + ub_{1} + vb_{2}, z = z_{1} + uc_{1} + vc_{2}$.

Probably the lesson here is that, whatever you're doing, you don't want to be doing it with parametric equations. I could be wrong. - Nov 22nd 2010, 08:48 AMbenoix
Hi Ragnar,

Thank you very much for your answer! In fact i do need to sample data on the surface of the cube (or more precisely on a $\displaystyle C^1$ surface very close to the cube).

That's to find an optimal configuration of points on the cube for a given energy ( minimization with least square criteria).

The best would be maybe to look at spherical coordinates, it might be more easy...

Thanks again