how to sort Indices of a circle in a 3d plane clockwise?

Hi,

I have a sort of dots circle in a 3d plane and I want all the indices of the dots to be arranged clockwise. the indices of the dots are attached. Do you know how to do that?

[Roger Stafford]

(Copied from http://www.mathworks.com/matlabcentral/newsreader/view_thread/333601):

In three dimensions the notion of clockwise versus counterclockwise loses its meaning. The notion of clockwise rotation is strictly a two-dimensional concept. It has the same indeterminacy as trying to distinguish between the two sides of an arbitrary three-dimensional plane. Which side is the "plus" side and which is the "minus" side?

[Mischa Kim]

Good point, Roger. Mathematically absolutely correct. From an engineering perspective I would argue that there is a somewhat "obvious" (and therefore in that same sense mathematically not necessarily definable), acceptable solution to the problem.

Answer 1

[Mischa Kim]

From the x and y data (from ind.mat) compute the polar angles of the dots using atan2. Add the polar angles as the fourth row to the matrix. Then use the sort command to sort the dots in descending order (in terms of angles).

[ELI]

Works grate except that it's needed to subtract the mean of x from x and the mean of y from y in order to set the center of the circle at the origin.