Committing on procedurally rigging a character takes a few things, some of which I realized this week when I was challenged while creating the spine rig setup on top of my base rig. To save time in the initial days, I didn't even consider the part where I should have spent some time to create a good quality base rig because throughout the process of creating this autorig, I will have to use (import) this base rig 100s of times.
I was using a previous rig I worked on which was pretty basic and I thought, that could be good for base rig. But I didn't know that a basic rig doesn't always mean a base rig. I won't even bother telling about my basic rig because it doesn't matter, what I want to emphasize on is the base rig. As per my knowledge, "Base" rig is the rig that is clean, is in a hierarchy, has the number of joints you will actually need in the process of creating the procedural rig, must have the best possible joint orientation.
What I did wrong was that my current base rig has only 3 spine joints and when I am scripting to create an IK spline spine, I cannot have a good spine with just 3 spine joints. If I want to work with that, which I won't since I wouldn't want 3 joint spine at least for human rig, I will have to have multiple control vertex in the spine curve and even that won't give good deformation.
I got my spine rig setup this week. I spent some time skinning the rig manually, to confirm whether the joints are getting skinned properly or not. bSkinSaver script is so helpful to save and load skin weights, now that I know how it works. I found the "base" rig issue after skinning process and currently, my code is having issue creating clusters for the spine curve. I think, I'll have to create a good base rig for the character and skin it before moving forward. I wish I could somehow skip this part but I know I need to do it, and after all, that is the reason I'm learning procedural rigging.
I found that even after creating a base rig, I had to add locators at the points where I wanted to create controls, such as chest, pelvis, etc. So, I added the locators in the specific positions and name it properly so that in future, if I want the controllers to be at a different location, I will just need to change the translation of the locator. We used locators because we needed only the translate node, not the shape node. Also, I added the spine curve manually in the base rig with a proper naming convention so that controls are created procedurally based on their name.
P.S.- My focus now is on procedurally rigging a biped character. Going forward, if I found that I got enough time, I'll start creating the autorig. Will try to make this procedural rig script in such a way that I can give it to others to test with their own characters.