title: Rigid and non-rigid geometrical transformations of a marker-cluster and their impact on bone-pose estimation.
abstract: When stereophotogrammetry and skin-markers are used, bone-pose estimation is jeopardised by the soft tissue artefact (STA). At marker-cluster level, this can be represented using a modal series of rigid (RT; translation and rotation) and non-rigid (NRT; homothety and scaling) geometrical transformations. The NRT has been found to be smaller than the RT and claimed to have a limited impact on bone-pose estimation. This study aims to investigate this matter and comparatively assessing the propagation of both STA components to bone-pose estimate, using different numbers of markers. Twelve skin-markers distributed over the anterior aspect of a thigh were considered and STA time functions were generated for each of them, as plausibly occurs during walking, using an ad hoc model and represented through the geometrical transformations. Using marker-clusters made of four to 12 markers affected by these STAs, and a Procrustes superimposition approach, bone-pose and the relevant accuracy were estimated. This was done also for a selected four marker-cluster affected by STAs randomly simulated by modifying the original STA NRT component, so that its energy fell in the range 30-90% of total STA energy. The pose error, which slightly decreased while increasing the number of markers in the marker-cluster, was independent from the NRT amplitude, and was always null when the RT component was removed. It was thus demonstrated that only the RT component impacts pose estimation accuracy and should thus be accounted for when designing algorithms aimed at compensating for STA.
authors.affiliation: Department of Movement, Human and Health Sciences, Università degli Studi di Roma ''Foro Italico'', Rome, Italy; Université de Lyon, F-69622 Lyon, France; Université Claude Bernard Lyon 1, Villeurbanne, France; IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), F-69675 Bron, France; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Bonci
authors.affiliation: Department of Movement, Human and Health Sciences, Università degli Studi di Roma ''Foro Italico'', Rome, Italy; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy. Electronic address: valentina.camomilla@uniroma4.it.
authors.forename: V
authors.initials: V
authors.lastname: Camomilla
authors.affiliation: Université de Lyon, F-69622 Lyon, France; Université Claude Bernard Lyon 1, Villeurbanne, France; IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), F-69675 Bron, France; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Dumas
authors.affiliation: Université de Lyon, F-69622 Lyon, France; Université Claude Bernard Lyon 1, Villeurbanne, France; IFSTTAR, UMR_T9406, Laboratoire de Biomécanique et Mécanique des Chocs (LBMC), F-69675 Bron, France; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Chèze
authors.affiliation: Department of Movement, Human and Health Sciences, Università degli Studi di Roma ''Foro Italico'', Rome, Italy; Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Università degli Studi di Roma "Foro Italico", Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Cappozzo
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000502:physiology*; D006801:Humans; D008962:Models, Theoretical; D010780:Photogrammetry / Q000379:methods; D012399:Rotation; D016138:Walking / Q000502:physiology*
keywords: Human movement analysis; Modelling; Rigid motion; Soft tissue artefact; Soft tissue deformation