Where is the query located that populates the Select Category popup?

Hi Mike. A few weeks ago I purchased SIM Gallery after you replied to my pre-sale question that you would assist in locating a piece of code as I am trying to make SIM Gallery work with JomSocial Groups. I am now working on this, so here is my question. Where (i.e. the file path/name and line number) is the query code that pulls the list of available categories to display in the popup when you click the "Select Category" button on the edit album page?

Thanks in advance for the guidance-

Tim