Clarify the difference between rounding digits and significant digits

[martijn-heil]

I wonder, what exactly is the difference and how should these be used properly?

[pnorman]

I can't recall off-hand, it's been too many years since I've touched the code.

[martijn-heil]

Bugger, lol. Before I posted this I read the code, but why there's rounding digits and significant digits still didn't really make sense to me. If I remember correctly, from reading it, it seems like it's to snap new nodes to already-produced nodes in a way if they fall within a certain margin of error or something like that. I might be wrong, though. It's been some time since I last read it too.

[pnorman]

My guess is that one is for snapping nodes together, the other is for how many digits to output, which has a major influence on file size.