I have what I think should be a relatively simple question.  I am trying to make a 3D image of a region of a cosmological simulation, and plot points in the image.  I define my region with box(left_edge,right_edge) where left_edge and right_edge are in code units.  However, the points that I read in from an earlier file are in cgs units.  Since the file was written using yt output, I would like to just let yt do the conversions, but nothing has units attached.  I want the 3d image to get everything into the same units.  I feel like there are a few ways I could fix this problem--1)  tell yt that my points are in cgs units, 2) force the create_scene to be in cgs units, 3) get yt to tell me the conversion factor from code units to cgs units.  

Unfortunately, I don't know how to do any of these things!  

Can someone give me some advice on what to do here?

Thanks!

Stephanie