I had a bit of spare time over the holidays so I set myself a side project to work on when I got a spare moment.
I decided to try my luck with a custom locator as I've never built one before but I wanted to make it useful in some way so I went for a pose-reader! Yea..very original I know. But it's always a staple in any riggers toolkit (whether as a plugin or just straight out the box Maya nodes).
This video by Marco Giordano helped me get my maths straight on the subject and I had to read up a bit about spherical co-ordinates to build the cone points at the correct place given some angle.
Unfortunately it's legacy viewport only. The scripted examples (Python API) for custom locators in the devkit seem to be..well...a bit of a mess. So I skipped VP 2.0 support. I'm lazy.