[PD] spherical vector addition

[Mathieu Bouchard]

On Thu, 26 Jun 2003, Cyrille Henry wrote:

> adding 2 spherical vector element by elements does not output the same 
> result.

No, it certainly does not. Adding spherical vectors like that has a
different meaning from usual addition, and frankly, I don't see how that
can be useful anywhere. If you want to do linear (cartesian) addition, you
have to get back into linear coordinates, add, and convert back to
spherical coordinates; or else, if there is a shortcut, it's quite
complicated.

The opposite, assuming linear coordinates, and then making a switch to
spherical/cylindric when necessary, is what makes most sense to
me. Especially because _then_ there are many shortcuts that you can
take: e.g. you can do rotation in linear coordinates using almost only
multiplications and additions.