Rigging in Animation: What Is It and Why It Matters


In the world of 3D medical animation, there is an entire jargon that can leave the average person confounded. Computer animation design-centric terms such as NURBS, bezier, rigid bodies, and follow through are a few examples that will likely send most people to the search engine. On this list is rigging. What is rigging in animation, and why does it matter?

model of bacteria

Let’s analyze.

Rigging (or skeletal animation) is a way to build the underlying structure of a character or other articulated object using series of interconnected digital bones or “joints”.  The hierarchical set of interconnected joints collectively forms the skeleton, or rig, of the object. Therefore, the process for creating the bone structure of a 3d model is known as rigging, and it can be used to help manipulate a 3D object like a marionette puppet similarly to how a skeleton would act in real life.

When making the model, designers can see the bones of the rig via computer software using a  3D view, but the bones are hidden beneath the mesh when the final model is put into action. By creating this invisible skeleton, rigs add an element of control to the animation process as they help solidify a model’s constitution and avoids deformities in the character they create.

Computer software allows rigging artists to view their renderings from several perspectives, allowing them to spot potential deformities in the animated character’s bone structure before the animation is recorded. Some key points that rigging artists will be looking out for when designing their 3D skeleton include:

  • Number of joints – joints in rigged skeletons are very similar to the joints in a human skeleton—they guide and control movement. With this in mind, the rigging artist will want to add more joints in the areas of the model that demand a higher degree of control, as fewer joints in the model will lead to more mechanical movements.
  • Rig hierarchy – for the end motion to be realistic, the rig must be designed logically. As rigs operate under a parent/child relationship, the corresponding joints must be created in the proper size and scale. For example, the shoulder joint should supersede the elbow joint, which should supersede the wrist joint.
  • Inverse kinematics (IK) built into the rig – while the logical hierarchy of the rig takes precedent, it is also essential for the rigging artist to rig for inverse kinematics. This is the process through which the motion of the skeleton works opposite of logic. For example, for an animated character to demonstrate a push-up, the child wrist joint should remain while the parent’s elbow joints move.
  • Control curve opportunities – the rigging artist can help the animator by grouping a set of rigged joints together using a control curve. This cluster of grouped joints has its control placed outside of the rigged skeleton. It allows the animator to move the entire group of joints in a single motion without individually manipulating each bone.

Based on this information, it can be seen how the rig for an animated character works in much the same way as the skeleton supports a human body. The digital bones in the rig act together to create virtual tissue that defines the movement of an animated object. This interconnected digital tissue creates a hierarchical environment in which the movement of a parent joint triggers movement in the “child” joint of the model unless the skeleton has been rigged for inverse kinematics.

It is a useful process for animation because rigs can create life-like motion of a model. Animators can then use the rig to help control the motions of the 3D model. As a result, the rig gives animators unprecedented control, flexibility, complexity, and fluidity of motion over more primitive animation techniques—all vital characteristics for effective medical animations.

When executed correctly, the rigged skeleton will bind seamlessly to the organic mesh, making the animated character’s motion highly convincing. This is an improvement over animation processes in which control over each individual body part/individual 3d object is required.

How Does Rigging in Animation Work?

Pretty much any type of object can be rigged. This has made it a popular technique in the entertainment industry, as it has helped modern cartoons display more life-like renderings of characters than more primitive animation techniques.

This application applies equally well to the medical field. For example, medical animation professionals can use rigging in animation to create realistic  interpretations of bones, joints, and organ systems. This can allow practitioners to create accurate simulations of how the body will behave.

It can also be highly beneficial when paired with 3D printing technology. For example, practitioners often have to create specialized prosthetics for specific patients, so having the ability to animate the prototyped piece in a digital simulation before execution can help eliminate much of the guesswork and trial and error associated with newly fabricated  materials.

The following breakdown looks at how rigging fits into the overall process of medical animation:

Surface Representation is Created

Prior to rigging, a model of the object must be created. Therefore, designers will create what is known as the surface representation of the object. Within the CAD world, this surface representation may also be referred to as the mesh or the skin. To the casual observer, the mesh may look like nothing more than a drawing of an arm, a leg, or bust.  That’s because the mesh, by itself, is nothing more than a model. As a surface representation, it needs some bones to give it life. This is where rigging comes in.

Skeleton is Assembled and Transformed

Once the mesh is in place, a skeleton is created to fit within the mesh. This may be a group of backbones, arm, leg, head bone, spine—basically any part of the body that matches the sketch the medical animator is trying to recreate.

After the bones of the skeleton have been put in place, designers can use animation software to transform the skeleton. This means that the position, rotation, and scale of the bones can be changed.

In a process known as keyframing, these transformations are recorded along a timeline, with these recorded instructions resulting in an animation of the 3d model.

How Rigging Improves the Animation Process

Rigging is an essential technique in the animation field because it allows computer designers to make realistic motion and deformation. By effectively using rigging techniques, modern 3D animation is far superior to traditional animation and stop motion animation, especially when precision in the medical field is necessary. Several factors allow rigging to yield superior animated renderings.

Hierarchical Instructions

Throughout the keyframing process, the recorded movements create a set of hierarchical instructions that the computer will repeat when moving an animated object. In this hierarchical structure, each bone in the rigged skeleton is part of a parent/child relationship with the other bones to which it connects in the rig, just like in a real organism. For example, if a hip bone is moved, the femur, knee, shin, and foot will all move as a result of these hierarchical instructions.

This simplifies the animation process for designers as it limits the number of instructions that they ultimately have to write and allows the animated object to imitate real life as accurately as possible.

Weight Painting

How the mesh interacts with the rig will be determined by a weight scale. Each bone within the model will control a certain amount, or weight, of mesh. Therefore, without some fine-tuning to the weight scale, some distortion in the animation may occur if certain bones within the rig carry too much influence over a particular section of the mesh.

A technique known as weight painting is used to effectively distribute the necessary portion of the skeleton to an assigned section of mesh. While the computer can often perform weight painting, some of the more intricate weight distribution challenges must be handled manually by a  design professional. While sometimes difficult to master, weight painting is critical in eliminating distortion from the animation.

Movement Constraints

Programming movement constraints are another essential element in ensuring that an animated image moves smoothly. To guarantee smooth movement, the animation software must be programmed to restrict certain types of movements from particular bones. For example, a knee must be programmed with the constraint that it can only bend backward. This again reflects nature.

Why Rigging is Important in Medical Animation

As mentioned, eliminating costly trial and error, and helping perfect best practices without consuming resources  are a couple of the benefits of rigging in animation. However, there are many other benefits of how the realistic models created by rigging can improve the medical industry.

Medical Simulation

There are a finite number of cadavers in the world on which doctors can practice their procedures. As a result, animation provides a potential solution to this shortage. However, the animation must depict a 100% accurate rendering to have any value, making the smooth, life-like interpretations of rigged 3D models the best choice.

Rigged 3D animation also has a potential wide-reaching impact on the medical school industry. Many students are scared away from school due to the high price tag associated with laboratory and hospital training fees. If rigged 3d  animation becomes universally adopted as a medical simulation tool, it may make medical school more accessible to a broader pool of candidates.

Cellular and Molecular Animations

Much of what we know about cells and molecules has been learned from under a microscope. While different types of animation have been used throughout the years to depict cellular processes in more convenient realms, rigged animation can create motions that are true to the cell.

Processes that 3D animation can help recreate include interplay between organelles, transcription of DNA, the molecular action of enzymes, the interaction between pathogens and white blood cells, and virtually any other sub-molecular process imaginable.

Pharmaceutical Mechanism of Action

Adopting pharmaceutical products can often be delayed when medical decision makers must digest their possible theoretical effects. To help in this regard, pharmaceutical manufacturers may use rigged animation to provide action clips that help explain how a medication will work.

Emergency Care Instruction

Regardless of how much training a caregiver has received, it is often impossible to accurately simulate emergencies in a safe yet instructive manner, but rigging in animation can make this possible. Using animation in this way, novice practitioners can get a realistic look at how to administer CPR, abdominal thrust, mouth-to-mouth, AED, and other emergency care techniques.

Surgical Training

In addition to medical school training, rigging in 3D animation allows experienced surgeons to hone and expand on their craft. Whether by attempting new, risky, or vanguard procedures, surgeons can combine animation with virtual reality to practice their procedures without experimenting on patients.

Weaknesses of Rigging in Animation

Although rigging has allowed for superior control, fluidity, and complexity of motion in animated models, allowing for the most realistic animated characters possible, a couple of potential weakness have been pointed out:

  • A rigged skeletal system only represents a set of vertices and, taken independently, cannot accurately replicate the complexity of the human body
  • The realistic motion of the muscles and skin is only attained through the use of deformers and other secondary features

Best Practices of Rigging in Medical Animation

Although the section above expounded the exciting ways in which rigging in animation can be used in the medical field, it must be executed with 100% accuracy to make the animation admissible. As a result, whether you are a 3d designer contracting with a medical facility or creating animation in-house on company software, there are several important tips to help ensure that rigged animations turn out as accurately as possible.

Map Out Actions First

It is impossible to effectively rig an object without any idea about what that object will do. As a result, before placing a single bone, you must sit down and draw out a map of all action that needs to be animated.

It is best to start planning by assuming that the model will need to perform a broad range of motion. This can be achieved by adding more joints to the rig. As the number of joints increases, the range of possible motions will increase exponentially. This is vital in ensuring that characters in the animation are flexible, move smoothly, and can perform complex motions.

A best practice in the medical animation industry is to create a rig that can perform all of the same movements that a human can. This will allow your object to adapt to any unexpected events in a simulation.

Don’t Over Rig the Object

Although the importance of adding multiple joints for a broad range of motions was just mentioned, it is also essential to avoid over rigging an object.

As the rigger and animator are often separate entities for most projects, talk to the animator and determine exactly what the animated model will be used for. Suppose the animation is intended to simulate an operating room procedure for knee surgery. In that case, you do not need to waste valuable time implementing complex facial rigs for the animated patient.

Ensure that the Rig is Properly Scaled

The correct anatomical placement of bones and joints is critical for animation in the medical field. While this may seem like common sense, cartoons and other types of entertainment animation may try to create surreal effects with their characters, so be sure that the placement of all body parts is scaled to ensure anatomical accuracy.

Without the correct anatomical rigging, the animation will appear distorted. Two exceptions to this rule are the knee and elbow joints. You will want to rig these joints a little closer to the skin instead of directly in the center of the limb to create the realistic protrusion that occurs when the joint is bent.

Use Deformers for Facial Rigging

The standard rigs used for bones and joints throughout the body will not work when rigging the face, as the eyebrows and cheekbones will require a stretchier, more organic rig.

Deformers can help in this regard. A deformer is a set of computer algorithms that can “move large sections of a model to simulate organic shapes and movement” with greater accuracy than standard rigs.

For example, with eyebrows, you could run a wire deformer along the brow to create precision when conveying emotion. If you need to create wrinkles in your character, a cluster deformer may be a strong bet, as cluster deformers allow the animator to control many vertices at once.

Take Advantage of All Perspectives

When building the rig, use multiple camera views to ensure that the rig fits the skin along all three dimensions. This should not be too difficult, as 3D animation software has grids that will allow you to judge the size and shape of the skeleton within the mesh.

Make sure to use a front view, bird’s eye view, and profile view. Taking advantage of these different perspectives allows you to pick out any anomalies in your rig—especially those that could potentially create a deformation.

The Best Rigging Software for 3D Medical Animation

While the virtues of rigging in animation have been extolled for its ability to create the most life-like animations in the industry, it is critical to choose the right platform to get the most out of potential rigging capabilities.

While 3D animation packages will come with rigging capabilities as part of the bundle, each will have subtle differences that may or may not appeal to your particular needs. The following are some great products that can help you effectively incorporate rigging techniques into your facility’s medical animation efforts.

  • Moka Studio – In addition to having support for motion capture techniques that can be applied to rigs, allowing for increased realism and faster development, Moka Studio has rolled out new technology for controlling rigged characters in real-time.
  • MayaThis is the industry standard for 3D animation. Used by the largest number of animators across the country, many rigging artists are adept at providing top-notch rigs on this platform. It provides all of the essential elements required for rigging a realistic medical model and is intuitive to navigate for less experienced riggers.
  • BlenderThis is an open-source animation software that is totally free. This makes it a strong choice for entities exploring the power of rigging in animation for science. While Blender has all of the tools necessary to rig and animate a model, it is not quite as powerful or comprehensive in its features as Moka Studio or Maya.
  • Mixamo – This is another strong option for novice rigging artists and an excellent product for professionals looking to rig their objects on the fly. Mixamo automates the rigging and weight painting process so that you can quickly see what your models look like in action. The platform also offers a host of default rigs that can be customized to create original object motions.
  • MakeHumanMakeHuman is a strong platform for creating generic human-like characters. It can be beneficial in a medical setting because it allows you to quickly customize models based on height and weight, with the product automatically rigging the model once these dimensions are inputted.

 

Below is a good video on human model 3d rigging by James Taylor:

 

Conclusion

Rigging in animation, or skeletal animation, is a computer animation technique used to represent a 3D object using a series of interconnected digital bones. It is essential in medical animation because, when properly deployed within a skin, quality rigs can allow the animator to control the model like a puppet, creating flexible, realistic designs unmatched by any other animation technique.  Such animation offers a host of cost-effective benefits that have the potential to improve the medical industry through life-like simulations.

I hope this article has helped you understand rigging better.  Click the following link to learn how to bake animation.

Dr. J

Dr. J has worked in biology all his life and holds several advanced degrees and certificates in biology, anatomy, scientific illustration, 3d animation and motion graphics. He has always had an interest in teaching others the wonders of biology using the latest advances in graphics, including visualization, digital microscopy, animation, illustration, VR and interactive media.

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