EDEM API: Custom particle factory

Hi,

I am looking to employ a custom particle factory depending on the height of the packed bed. I have a vertical column of a packed bed of particles. The height of the bed starts to reduce in the column as the particles are removed from the bottom. As the bed height falls below a certain level, I would like a certain amount of particles to be injected into the column at the top so that the bed height is increased again. I was thinking of accessing the location of particle to get an estimate of the bed height. Could anyone guide me on how to gain access to location of the particles using Factory API?