custom touch getures

I'm using the excellent fingergestures library.

I want to write some custom gestures. I'm wondering if anyone has any advice for writing: a circle gesture, a swipe down, then up and to the side, a semi circle down then up and to the side.

I have some ideas for how to do this in a crude fashion (record all the points, then perform some sanity checks, then go through them to check for my approximate shapes). just wanted to see if this was the right course, or perhaps someone has already seen something else..