Université de Lyon, F-69622, Lyon; IFSTTAR, LBMC, UMR_T9406, Bron; Université Lyon 1, Villeurbanne, France.
Department of Movement, Human and Health Sciences, Università degli Studi di Roma "Foro Italico", Rome, Italy.
J Biomech. 2014 Jan 22;47(2):476-81. doi: 10.1016/j.jbiomech.2013.10.034. Epub 2013 Nov 9.
While reconstructing skeletal movement using stereophotogrammetry, the relative movement between a skin marker and the underlying bone is regarded as an artefact (soft tissue artefact: STA). Similarly, the consequent pose, size and shape variations that affect a cluster of markers associated with a bony segment, or any arbitrary change of configuration in the marker local positions as representative of the skin envelope shape variation, may also be looked upon as an STA. Bone pose estimators able to compensate for these artefacts must embed relevant a priori knowledge in the form of an STA mathematical model. Prior to tackling this modeling exercise, an appropriate definition and mathematical representation of the STA time histories must be accomplished. Relevant appropriateness is based on the degree of approximation of the STA reconstruction and on the number of parameters involved. The objective of this study was to propose a generalized mathematical representation of the STA which would be applicable for most plausible definitions of it. To this purpose, a modal approach was used that, most importantly, allows for the splitting of a given STA into additive components (modes). For each STA definition, these modes may be ranked according to the contribution that each of them gives to the reconstruction of the STA. In this way, the STA definition leading to the minimum number of modes, and, therefore, of parameters, that provides an adequate approximation for further purposes can be selected, allowing a trade-off between complexity and effectiveness of the STA model. Using information available in the literature and data provided by an ex-vivo experiment, it is shown that the modes corresponding to the different STA definitions (individual marker displacements, marker-cluster geometrical transformations, and skin envelope shape variations) can be ranked and selected leading, respectively, to a large, moderate or low number of parameters embedded in the STA mathematical representation.
在使用体视摄影测量重建骨骼运动时，皮肤标记物与下方骨骼之间的相对运动被视为一种伪影（软组织伪影：STA）。同样，影响与骨段相关联的一组标记物的后续姿势、大小和形状变化，或任何代表皮肤包络形状变化的标记物局部位置的任意配置变化，也可能被视为 STA。能够补偿这些伪影的骨骼姿势估计器必须以 STA 数学模型的形式嵌入相关的先验知识。在进行此建模练习之前，必须完成对 STA 时间历史的适当定义和数学表示。相关性的适当性基于 STA 重建的近似程度和涉及的参数数量。本研究的目的是提出一种适用于大多数 STA 合理定义的通用数学表示。为此，使用了模态方法，最重要的是，允许将给定的 STA 分解为可加组件（模态）。对于每个 STA 定义，可以根据它们对 STA 重建的贡献对这些模态进行排序。通过这种方式，可以选择导致最少模态（因此参数最少）的 STA 定义，从而为进一步的目的提供足够的近似值，从而可以在 STA 模型的复杂性和有效性之间进行权衡。使用文献中提供的信息和离体实验提供的数据，表明可以对对应于不同 STA 定义的模态（单个标记物位移、标记物集群几何变换和皮肤包络形状变化）进行排序和选择，分别导致嵌入 STA 数学表示中的大量、中等或少量参数。
