A Comparison of Design Strategies for 3D Human Motions
Summary (3 min read)
1 Introduction
- In this paper the authors compare the design strategies for 3D human motion.
- The authors can order the various methodologies along a scale beginning at high realism for the motion design process in a production context, then middle realism for the interactive process provided by a wide range of motion modeling systems and finally low realism for real-time applications as simulators, virtual reality and games.
- Then, in the second part the authors focus on the wide range of systems providing interactive response time basically for design purpose or for some of them dedicated to human factors evaluation.
- The objectives of the ESPRIT project HUMANOID 2 are recalled in that context.
2 Motion Design in Film Production Context
- What is required in movie productions is much more than the mere physically-based realism ; it is rather a high believability conveying the intention of the motion and the emotional state of the character.
- Such practical knowledge can now guide the 3D animators [2][3] in bringing to "life" cartoon-like or toy-like characters as recently demonstrated with the movie "Toy Story" [4].
- Apart from that masterpiece which involved an important team (110 persons at Pixar [4]), this type of work is limited to short pieces for cost reasons.
- At this moment, most of them are special effects, commercials and, more and more, some sophisticated games [5].
- The logical requirement on the software tools is to ask both for the highest realism and the greatest freedom of design in order to edit and improve any detail of the motion.
2.1 Physics alone does not bring “Life”
- The major commercial systems for 3D human animation, as Alias-Wavefront-TDI and Softimage, propose various degrees of motion realism from the standard Keyframe techniques, Inverse Kinematics, Direct and Inverse Dynamics to the option of live recording.
- This is achieved with the large set of tools manipulating keyframes [4].
- Such requirements discard language-based interfaces in this context [8][9].
- This explain why the Performance Animation approach has been widely adopted in the film production context [14][5].
2.2 Live recording techniques are still too “superficial”
- Most of the Performance Animation systems dedicated to the recording of human body motion belong to two groups depending on the sensing technologies they rely on, either optical or magnetic.
- Both allow the real-time registration of the human motion, practically speaking from around 20Hz to 100Hz for magnetic, and from 50Hz to 200Hz for optical.
- Locating the anatomical frame at each joint of interest by applying a rigid transformation from the technical frame (or magnetic sensor frame) deriving the anatomical angles from the relative orientation between anatomical frames belonging to successive segments at a given joint.
- There is also a need to improve motion editing methods in order to enforce the cartesian constraints lost in the acquisition process while retaining the initial motion dynamics [20] [12].
3 The interactive simulation environment
- Apart from the wide range of commercial systems providing interactive response time for the purpose of animation design, the authors can consider here the systems dedicated to human factors evaluation, ergonomics, human behaviors studies and autonomous agent simulations.
- An equally important property of this technique is the ability to combine it with goal-oriented motions (defined with Inverse Kinematics) in a hierarchical fashion [7].
- Some interesting generalization of the transition management between multiple postures have be proposed to define simple behaviors that can also be used in real-time applications [32].
- This branch has begun with simple flock of birds and animal herds behaviors and now turns to simulate believable human behaviors in complex environments [22].
4 The real-time simulation environment
- The real-time simulation environment fully integrate the end-user within the animation loop in order to drive strategic simulation parameters.
- In that context, only very small system lag is acceptable in response to user input.
- Only simple characters can be animated in such a way due to the limited number of measured DOFs (even if more than one puppeteer are coordinating their performance, one usually animates the body while the other one animates the face).
- Even in that limited context it can be desirable to automatically alter the displayed hand posture in order to reflect the virtual hand interaction with the virtual objects [37].
5 The HUMANOID environment
- The HUMANOID environment is dedicated to the development of multimedia, VR and CAD applications involving virtual humans [26].
- The displacement is realized as an automatic secondary behavior of the Inverse Kinematics solution [7].
- It is achieved, for each step of the end effector behavior, in a two stages process : construction of each sensor’s kinematic jacobian which is inverted and multiplied to the correction displacement to get the correction posture variation of the character.
- The gravity and collision avoidance can be added thus automatically producing realistic postures as a background behavior.
- The second issue the authors want to highlight here is the interest of specifying the body motion from keyframed motion assigned to grasped objects.
6 Conclusions
- The authors have reviewed the various strategies used to animate 3D human characters by grossly classifying them in three classes of compromise between the requirements of motion realism and real-time interaction.
- On the other hand, some class of viewers can accept the imperfection of the displayed motion, whatever the production tool, if it allows a greater interaction.
- The design strategies for 3D human motions have been the object of important researches since the beginning of the 80s.
- Now and for the years to come, the considerable interest which has supported them is still raising as the computing power only begins to allow convenient handling of these classes of problems.
- Moreover, significant advances are soon to emerge in the direction of autonomous agents reacting to each other and to their environment.
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Citations
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Cites background from "A Comparison of Design Strategies f..."
...The design time is greatly reduced compared to pure keyframe design even if a second stage of motion refinement is to be planned after the capture [7]....
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...Design of human motion is a complex task and an active research area [7]....
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References
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"A Comparison of Design Strategies f..." refers background in this paper
...This branch has begun with simple flock of birds and animal herds behaviors and now turns to simulate believable human behaviors in complex environments [22]....
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...In that context the realism is more a matter of conformance with the situations potentially faced by populations of future users of public environment [22], working place or device [23]....
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...For this reason a real human being naturally adopts the postures inducing the best comfort for a desired behavior [41]....
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"A Comparison of Design Strategies f..." refers background in this paper
...Although the resulting motion is less artistic, it remains nearly as realistic as a recorded one in term of space, time and phase characteristics [27] [28] [29]....
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