Figure 1: Yarn-level cloth: Three knitting patterns relaxed to rest in our simulator. Each starts from a flat input configuration like at left; they differ only in their interlocking patterns. Characteristic shapes and textures of each knit emerge from our yarn-level physical model. AbstractKnitted fabric is widely used in clothing because of its unique and stretchy behavior, which is fundamentally different from the behavior of woven cloth. The properties of knits come from the nonlinear, three-dimensional kinematics of long, inter-looping yarns, and despite significant advances in cloth animation we still do not know how to simulate knitted fabric faithfully. Existing cloth simulators mainly adopt elastic-sheet mechanical models inspired by woven materials, focusing less on the model itself than on important simulation challenges such as efficiency, stability, and robustness. We define a new computational model for knits in terms of the motion of yarns, rather than the motion of a sheet. Each yarn is modeled as an inextensible, yet otherwise flexible, B-spline tube. To simulate complex knitted garments, we propose an implicit-explicit integrator, with yarn inextensibility constraints imposed using efficient projections. Friction among yarns is approximated using rigid-body velocity filters, and key yarn-yarn interactions are mediated by stiff penalty forces. Our results show that this simple model predicts the key mechanical properties of different knits, as demonstrated by qualitative comparisons to observed deformations of actual samples in the laboratory, and that the simulator can scale up to substantial animations with complex dynamic motion.
Figure 1: Stages of our knitted garment modeling system: (a) We begin our interactive modeling process with a polygonal mesh that specifies the global shape of the cloth model; (b) using this polygonal mesh we produce a high-resolution stitch mesh that serves as a canvas-like abstraction of the yarn model; (c) then, we specify the desired knitting pattern over the stitch mesh's surface. (d) Following the interactive modeling process, the model goes through offline relaxation, beginning with a mesh-based relaxation that moves the stitch mesh to the subdivision surface of the input model and slides its vertices over this surface based on the topology of the knitting pattern; finally, (e) we generate the yarn curves and (f) use a physically based relaxation process at the yarn level to compute the final realistic shape. AbstractRecent yarn-based simulation techniques permit realistic and efficient dynamic simulation of knitted clothing, but producing the required yarn-level models remains a challenge. The lack of practical modeling techniques significantly limits the diversity and complexity of knitted garments that can be simulated. We propose a new modeling technique that builds yarn-level models of complex knitted garments for virtual characters. We start with a polygonal model that represents the large-scale surface of the knitted cloth. Using this mesh as an input, our interactive modeling tool produces a finer mesh representing the layout of stitches in the garment, which we call the stitch mesh. By manipulating this mesh and assigning stitch types to its faces, the user can replicate a variety of complicated knitting patterns. The curve model representing the yarn is generated from the stitch mesh, then the final shape is computed by a yarn-level physical simulation that locally relaxes the yarn into realistic shape while preserving global shape of the garment and avoiding "yarn pull-through," thereby producing valid yarn geometry suitable for dynamic simulation. Using our system, we can efficiently create yarn-level models of knitted clothing with a rich variety of patterns that would be completely impractical to model using traditional techniques. We show a variety of example knitting patterns and full-scale garments produced using our system.
Figure 1: Stages of our knitted garment modeling system: (a) We begin our interactive modeling process with a polygonal mesh that specifies the global shape of the cloth model; (b) using this polygonal mesh we produce a high-resolution stitch mesh that serves as a canvas-like abstraction of the yarn model; (c) then, we specify the desired knitting pattern over the stitch mesh's surface. (d) Following the interactive modeling process, the model goes through offline relaxation, beginning with a mesh-based relaxation that moves the stitch mesh to the subdivision surface of the input model and slides its vertices over this surface based on the topology of the knitting pattern; finally, (e) we generate the yarn curves and (f) use a physically based relaxation process at the yarn level to compute the final realistic shape. AbstractRecent yarn-based simulation techniques permit realistic and efficient dynamic simulation of knitted clothing, but producing the required yarn-level models remains a challenge. The lack of practical modeling techniques significantly limits the diversity and complexity of knitted garments that can be simulated. We propose a new modeling technique that builds yarn-level models of complex knitted garments for virtual characters. We start with a polygonal model that represents the large-scale surface of the knitted cloth. Using this mesh as an input, our interactive modeling tool produces a finer mesh representing the layout of stitches in the garment, which we call the stitch mesh. By manipulating this mesh and assigning stitch types to its faces, the user can replicate a variety of complicated knitting patterns. The curve model representing the yarn is generated from the stitch mesh, then the final shape is computed by a yarn-level physical simulation that locally relaxes the yarn into realistic shape while preserving global shape of the garment and avoiding "yarn pull-through," thereby producing valid yarn geometry suitable for dynamic simulation. Using our system, we can efficiently create yarn-level models of knitted clothing with a rich variety of patterns that would be completely impractical to model using traditional techniques. We show a variety of example knitting patterns and full-scale garments produced using our system.
Figure 1: Yarn-level cloth: Three knitting patterns relaxed to rest in our simulator. Each starts from a flat input configuration like at left; they differ only in their interlocking patterns. Characteristic shapes and textures of each knit emerge from our yarn-level physical model. AbstractKnitted fabric is widely used in clothing because of its unique and stretchy behavior, which is fundamentally different from the behavior of woven cloth. The properties of knits come from the nonlinear, three-dimensional kinematics of long, inter-looping yarns, and despite significant advances in cloth animation we still do not know how to simulate knitted fabric faithfully. Existing cloth simulators mainly adopt elastic-sheet mechanical models inspired by woven materials, focusing less on the model itself than on important simulation challenges such as efficiency, stability, and robustness. We define a new computational model for knits in terms of the motion of yarns, rather than the motion of a sheet. Each yarn is modeled as an inextensible, yet otherwise flexible, B-spline tube. To simulate complex knitted garments, we propose an implicit-explicit integrator, with yarn inextensibility constraints imposed using efficient projections. Friction among yarns is approximated using rigid-body velocity filters, and key yarn-yarn interactions are mediated by stiff penalty forces. Our results show that this simple model predicts the key mechanical properties of different knits, as demonstrated by qualitative comparisons to observed deformations of actual samples in the laboratory, and that the simulator can scale up to substantial animations with complex dynamic motion.
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