PIE Ud-

Hello again,

Continuing on much the same vein as before, I was looking at the term
Ud-. It seems almost every meaning attached to it carries the sense
of 'out/outside of'.
This then made me ponder how the Germanic Uz- 'out' produced the OHG
Ur 'original'.
It seems strange that 'out' would produce 'original'. If anything one
would expect Ur to carry the sense of 'derivative' or something akin
to 'that which develops outward from' , rather than meaning the
original core/root.

I'm just wondering if anyone could clarify this development for me, and
how 'out' came to mean 'original'?

Additionally, if there is no clear explanation; is it possible that the
OHG Ur (original) stems not from Ud-, but rather from Or- or Er-??

Many thanks for your time,
Aydan