BASH - Biomechanical Animated Skinned Human

Schleicher, R., Nitschke, M., Martschinke, J., Stamminger, M., Eskofier, B., Klucken, J., Koelewijn, A. (2021). BASH: Biomechanical Animated Skinned Human for Visualization of Kinematics and Muscle Activity. 16th International Conference on Computer Graphics Theory and Applications (GRAPP), 2021.

https://www.scitepress.org/Papers/2021/102106/102106.pdf

BASH Model

Converting a OpenSim [1] format file (.osim + .mot) to the SCAPE [2] framework. Visualization tool to inspect the animated model in 3D.

Processing Pipeline

Input Model: OpenSim

• Parser
• Model (.osim)
• Scale factors (.xml)
• Motion (.mot)
• Muscle Activation (.sto)

Baseline model Design for a new Musculoskeltal Model (in Blender)

• modeling
• import SCAPE mesh
• rig and skin skeleton (same hierarchy as musucloskeletal model)
• place markers (same set as musculoskeletal model)
• export model (.dae reorders vertices...) => mesh, markers & weights files

Scaling

• performed automatically, applied correctly to the hierachy, applied in bone space
• use .xml file or my estimation (defined in settings.h)
• scaled vs generic in ./data/cache/mesh/

Initial Pose Matching

• computed automatically using OpenSim's IK solver
• cached in ./data/cache/mapping for debugging the resulting .mot file

Pose Transformation

• calculated beforehand (needed the mesh for projection to SCAPE)
• uses pose mapping projection and kinematic transformations, applied in world space
• cached in ./data/cache/mesh/

Projection into SCAPE space

• projection to scape space (only relative rotations)
• rigid alignment to adjust translation
• cached in ./data/cache/mesh/

Visualization of Muscle Activation

• computed at run-time
• color coding in Fragment Shader

Settings

• settings.h for keyshortcuts, constants and other configurations

Project structure and dependencies

• SCAPE: The main Windows-Application that handles the model conversion and visualization

• External dependencies (minimum required version):

• SFML (>= 2.5.1)

• glew (>= 2.1.0)

• glm (>= 0.9.9.5)

• Assimp (>= 3.0.0)

• OpenSim and SimbodyTK (>= 4.0)

• libRender: A custom framework used for creating a window and render a 3D-application in it

• External dependencies (minimum required version):

• SFML (>= 2.5.1)

• glew (>= 2.1.0)

• glm (>= 0.9.9.5)

• libSCAPE: The SCAPE framework to load the SCAPE binary data and create a mesh in pose and shape

• External dependencies (minimum required version):

• SuitSparse package: suitsparse + amd + umfpack (>= 5.1.2)

• GSL (>= 2.4)

SCAPE Framework

• Implementation in ´SCAPE.h´
• Model parameters
• Pose: Rotation vector for each part ('numParts = 16') in three-dimensional twist subvectors (the axis is determined by the vector's direction and the angle is determined by the vector's magnitude.
• Shape: Scalar PCA coefficients ('numVecs = 20') to modify body proportions like height, size and gender etc.

Building platform x64

• OpenSim can only be built in 64bit. So we have to use the x64 Platform in order to use their API.
• Include and link all dependencies in x64.
• Build the SCAPE framework in x64.
• Define the flag '#define SAVE_MATRIX 0' once to write new binaries in the correct format (64bit wording).
• The folder 'data\default_scape_data' should contain the binary files: 'matrixDGrad.bin', 'SCAPE_DGrad_numeric.bin', 'SCAPE_DGrad_symbolic.bin', 'SCAPE_pose.bin'.

Example result

OpenSim's visualization compared to our visualization (data set: straight running [3]):

References

[1] Seth, A., Hicks, J. L., Uchida, T. K., Habib, A., Dembia,C. L., Dunne, J. J., Ong, C. F., DeMers, M. S., Ra-jagopal, A., Millard, M., et al. (2018). OpenSim: Sim-ulating musculoskeletal dynamics and neuromuscularcontrol to study human and animal movement. PLoSComputational Biology, 14(7):1–20.

[2] Anguelov, D., Srinivasan, P., Koller, D., Thrun, S., Rodgers,J., and Davis, J. (2005). SCAPE: Shape Completionand Animation of People. InACM Transactions onGraphics, volume 24, pages 408–416.

[3] Nitschke, M., Dorschky, E., Heinrich, D., Schlarb, H., Eskofier, B. M., Koelewijn, A. D., and Van den Bogert, A. J. (2020). Efficient trajectory optimization for curved running using a 3D musculoskeletal model with implicit dynamics. Scientific Reports, 10(17655).