particle emission from a fixed point?

Hello,

I would like to make a charged particle tracing simulation. It seems to me that I can only specify an inlet at the boundary of a domain, i.e. of finite extension. Is it possible to specify particle emission from a single point?

Another question: is it possible to emit particles according to 2D gaussian distributions (Twiss ellipses) in the (x,x') and (y,y') phase spaces? (x and y are the transverse coordinates to the propagation direction, and x' and y' are their derivatives w.r.t. the z coordinate). Do I need to do it using the API?

Thank you
Daniel