[Development in Progress]
"In its simplest form, 3D rigging is the process of creating a skeleton for a 3D model so it can move. Most commonly, characters are rigged before they are animated because if a character model doesn't have a rig, they can't be deformed and moved around. They are stuck in whichever pose the modeler decided to put them in. The rigging process can become very technical and seem overwhelming at times, but after a little practice you'll be creating great rigs in no time."
Biped Rig put together for a student short film. Requirements included vast facial emotion range and the ability to transform into a mermaid. The 3D model acquired had solid topology but its advised you break the mesh further before setting out to rig for a film.
Josh Sobel's "Expressive Facial Rigging" course is a great place to start for somebody with no experience with facial rigging for animation. This is what was used as reference to put together Sirena's facial rig. The course uses several instances of the face mesh, each with its own set of joints driving the mesh to get deformations for different parts of the face. It divides parts of the face among the many instances of the face mesh and all these meshes are input into the main mesh as blendshapes. Controls are created for the main mesh to drive the blendshapes. Sculpted blendshapes are also used as correctives and to achieve drastic and anatomically correct deformations on the mouth. This course is also an amazing primer to weight painting. Somebody with no real knack for weight painting will come out of this course with a strong grasp of how to do it efficiently and will be confident about handling other novel weight painting jobs. The facial rig approximately took about 3 weeks.
The course does not explicitly go over how to rig the eyebrows but the same "ribbon spline" technique as for the lips can be used to rig the eyebrows. For Sirena, exclusively geometry-based blendshapes were used for the eyebrows and one thing to keep notice of with such an approach is knowing that corrective blendshapes will absolutely be necessary for cases where you're activating more than 1 blendshapes. Before starting, you should know how to break the mesh down into parts and not having to duplicate the entire mesh when you only need a duplicate of the face for a blendshape. This tutorial should teach you how to separate the mesh. Also, this tool will literally save your life at one point or another. You will learn that how blendshapes work is by replicating the positions of the same vertices on another mesh and how Maya knows what vertex position to take for each vertex on the target mesh is using vertex numbers assigned to each vertex. Messing with the mesh, can lead to reordering of the vertices and this is where the aforementioned tool will come in handy.
Free resources I wish I'd known about before I set out to rig the face: UIW 3D Animation and Game Design's "Joint Based Facial Expression" course on Youtube. This goes over creating a far more complex and thorough facial rig. Great step by step walkthroughs, lots of learning.
The biped rig was based almost exactly off a beginner level PluralSight course. Though it did the job, the rig could've been better. The course doesn't really go into industry weight-painting pipelines and its advised to go through Josh Sobel's course first because it also acts as a primer for weight painting. Better resources for bipeds for film don't really explicitly exist, you'll have to gather bits and pieces but great resources for bipeds for games exist and are great learning tools for rigging for film as well. Jeremy Ernst's "Creature Rigging for Games" is an amazing course that every rigger should be familiar with. The facial rig approximately took about 1.5 weeks.
Transforming into a Mermaid
This was basically a hack. A separate model for the fish tail was bought and the initial plan was to stitch the meshes together. This, however would have required to go through the entire rigging + weight painting process over again and the ETC project schedule just doesn't allow it. The solution was to create a separate fish tail rig and move it over to the desired position in the world space so it looks like the biped model and the tail model are one. This was followed by applying an invisible texture to all the faces of the biped model that weren't part of the character as a mermaid (the legs and part of the hips).