I'm at the stage of adding control bones to all the chest deform bones. On checking I thought my right arm wasn't working properly - it turns out it was ok but it's generated this question/confusion
Looking at it - the symmetrization of the Left arm (with X pointing Global +Z) has the right arm with X pointing to Global -Z. Is this the way it's supposed to be?
Wayne has previously cautioned to 'just let the computer take care of the symmetry' but my natural instinct is to manually adjust the .R bones so the X is on global +Z as per .L
Yep that's the way it is suppose to be, Charles.
Bone Roll and symmetry is a really confusing thing and I will do my best to not add to your confusion. But do you remember the other day when I said something like "all you need to know for now, is to let the computer symetrize it for you"? This is the reason, you probably won't understand it for a long time - and that's fine. I don't need to know how my microwave works in order to heat things up as hot as the centre of the sun and burn the roof of my mouth off. (maybe that is just me)
Ok here we go.
---
Blender's co-ordinate system is Right Handed. https://en.wikipedia.org/wiki/Right-hand_rule
Different software are either left handed or right handed and rotate that hand in a particular way...and call that their coordinate system.
This is a mathematical derived system - X in the thumb, Y is the pointer and Z is the middle finger.
Blender is right handed with the hand rotated so the middle finger is sticking up. (so bad arse!)
This is the same for bones.
X is left/right, Y is the length of the bone, Z is up/down
These axes can never change - because.......well mathematics.
If you place a bone inside an armature on the left hand side of the character and symmetrize it this is what you get.
The bones are facing opposite orientations, with the x, y mirrored but the Z is pointing in the same direction.
Many people first think that this might be incorrect and try to get the axes all the same - or at least try to get the X axis flipped.
I would love to be able to show this inside Blender - but it isn't possible.
Why?
Because in order to do that, the bone on the right side (screen left) would need to change to the left handed coordinate system.
This isn't possible because....well mathematics.
As you know, Blender let's us position the head and tail of the bone, and then use this weird thing called Bone Roll, to aim that Z axis.
Under the hood, Bone Roll is really a 3 dimensional vector that is converted into a human readable angle (from -180 to +180). This is the best way to handle it in my opinion because you don't have to deal with a vector, and you don't have to orient the head and the tail individually (like in some software)
It does give you the same value for -180 and +180 but in the scheme of things, that's a better trade off.
Let the computer do the thinking for you.
Just position your head and tail, then point the Z axis where you want and symmetrize.
