I am continuing to bang my head trying to understand some aspects of families. I am currently trying to build a complete fixtures library for our Interiors group, and my head hurts trying to understand some of this.

I started by looking at the "Lighting Fixture ceiling based" template, and I get a Ref Level, along with the standard front, back, left and right elevations.

Then I looked at the "Downlight - Recessed Can" family from the OOTB Imperial Library. There I have a Ground Floor level, and a Level 2, and a ceiling object between. I don't understand the need for the Ground Floor, and I really don't understand needing to relate to the floor above!. My understanding is that you would use Linework in conjunction with an Underlay to show the light fixture in the Floor Plan. Or is the example fixture actually a special case that is intended to always show up in plan? And does the Ground Floor automatically relate to the actual floor level in some way? In other words, could I create a pendant fixture where the mounting plate always happens at the ceiling, but the height of the pendant is controlled relative to the floor, and changing ceiling height causes the cord to lengthen, the mount stays at the ceiling and the pendant stays put relative to the floor? And how to I add that Floor Level? Is it just the name that makes it relate to the actual floor level?

Inquiring minds want to know?

Thanks,
Gordon