Not strictly Houdini related, just a question from the mathematically challenged…

How can I convert a direction vector from cartesian to spherical coordinates?

I know the formula for a *position* (as well as the nodes topolar and frompolar) but not a vector… it's probably something simple that I'm overlooking…


Cheers,
Jon

Isn't a position just a vector, as well?

I'm not sure…

Direction vectors must be treated differently when doing a space transformation, so I assumed that applied to this as well.

wikipedia says

In mathematics, a spherical coordinate system is a coordinate system for three-dimensional space where the position of a point is specified by three numbers: the radial distance of that point from a fixed origin, its polar angle measured from a fixed zenith direction, and the azimuth angle of its orthogonal projection …

so you are missing two variables no, distance and azimuth angle

A direction vector is also a position on the unit sphere. You can use topolar for a direction vector, and it will return phi and theta, with r being the length of the vector (one if normalized).

Thanks, easier than I thought! And now makes more sense.