Odometria visual baseada em técnicas de structure from motion

Visual Odometry is the process that estimates camera position and orientation based solely on images and in features (projections of visual landmarks present in the scene) extraced from them. With the increasing advance of Computer Vision algorithms and computer processing power, the subarea known as Structure from Motion (SFM) started to supply mathematical tools composing localization systems for robotics and Augmented Reality applications, in contrast with its initial purpose of being used in inherently offline solutions aiming 3D reconstruction and image based modelling. In that way, this work proposes a pipeline to obtain relative position featuring a previously calibrated camera as positional sensor and based entirely on models and algorithms from SFM. Techniques usually applied in camera localization systems such as Kalman filters and particle filters are not used, making unnecessary additional information like probabilistic models for camera state transition. Experiments assessing both 3D reconstruction quality and camera position estimated by the system were performed, in which image sequences captured in reallistic scenarios were processed and compared to localization data gathered from a mobile robotic platform

Biomechanical modelling of human knee during living activities

The knee joint is a key structure of the human locomotor system. The knowledge of how each single anatomical structure of the knee contributes to determine the physiological function of the knee, is of fundamental importance for the development of new prostheses and novel clinical, surgical, and rehabilitative procedures. In this context, a modelling approach is necessary to estimate the biomechanic function of each anatomical structure during daily living activities. The main aim of this study was to obtain a subject-specific model of the knee joint of a selected healthy subject. In particular, 3D models of the cruciate ligaments and of the tibio-femoral articular contact were proposed and developed using accurate bony geometries and kinematics reliably recorded by means of nuclear magnetic resonance and 3D video-fluoroscopy from the selected subject. Regarding the model of the cruciate ligaments, each ligament was modelled with 25 linear-elastic elements paying particular attention to the anatomical twisting of the fibres. The devised model was as subject-specific as possible. The geometrical parameters were directly estimated from the experimental measurements, whereas the only mechanical parameter of the model, the elastic modulus, had to be considered from the literature because of the invasiveness of the needed measurements. Thus, the developed model was employed for simulations of stability tests and during living activities. Physiologically meaningful results were always obtained. Nevertheless, the lack of subject-specific mechanical characterization induced to design and partially develop a novel experimental method to characterize the mechanics of the human cruciate ligaments in living healthy subjects. Moreover, using the same subject-specific data, the tibio-femoral articular interaction was modelled investigating the location of the contact point during the execution of daily motor tasks and the contact area at the full extension with and without the whole body weight of the subject. Two different approaches were implemented and their efficiency was evaluated. Thus, pros and cons of each approach were discussed in order to suggest future improvements of this methodologies. The final results of this study will contribute to produce useful methodologies for the investigation of the in-vivo function and pathology of the knee joint during the execution of daily living activities. Thus, the developed methodologies will be useful tools for the development of new prostheses, tools and procedures both in research field and in diagnostic, surgical and rehabilitative fields.

Spatial mechanisms for modelling the human ankle passive motion

Knowledge on how ligaments and articular surfaces guide passive motion at the human ankle joint complex is fundamental for the design of relevant surgical treatments. The dissertation presents a possible improvement of this knowledge by a new kinematic model of the tibiotalar articulation. In this dissertation two one-DOF spatial equivalent mechanisms are presented for the simulation of the passive motion of the human ankle joint: the 5-5 fully parallel mechanism and the fully parallel spherical wrist mechanism. These mechanisms are based on the main anatomical structures of the ankle joint, namely the talus/calcaneus and the tibio/fibula bones at their interface, and the TiCaL and CaFiL ligaments. In order to show the accuracy of the models and the efficiency of the proposed procedure, these mechanisms are synthesized from experimental data and the results are compared with those obtained both during experimental sessions and with data published in the literature. Experimental results proved the efficiency of the proposed new mechanisms to simulate the ankle passive motion and, at the same time, the potentiality of the mechanism to replicate the ankle’s main anatomical structures quite well. The new mechanisms represent a powerful tool for both pre-operation planning and new prosthesis design.

Slope stability analysis by multi-temporal DEMs and 3D modelling: The 2002 and 2007 Stromboli landslide events

Natural hazard related to the volcanic activity represents a potential risk factor, particularly in the vicinity of human settlements. Besides to the risk related to the explosive and effusive activity, the instability of volcanic edifices may develop into large landslides often catastrophically destructive, as shown by the collapse of the northern flank of Mount St. Helens in 1980. A combined approach was applied to analyse slope failures that occurred at Stromboli volcano. SdF slope stability was evaluated by using high-resolution multi-temporal DTMMs and performing limit equilibrium stability analyses. High-resolution topographical data collected with remote sensing techniques and three-dimensional slope stability analysis play a key role in understanding instability mechanism and the related risks. Analyses carried out on the 2002–2003 and 2007 Stromboli eruptions, starting from high-resolution data acquired through airborne remote sensing surveys, permitted the estimation of the lava volumes emplaced on the SdF slope and contributed to the investigation of the link between magma emission and slope instabilities. Limit Equilibrium analyses were performed on the 2001 and 2007 3D models, in order to simulate the slope behavior before 2002-2003 landslide event and after the 2007 eruption. Stability analyses were conducted to understand the mechanisms that controlled the slope deformations which occurred shortly after the 2007 eruption onset, involving the upper part of slope. Limit equilibrium analyses applied to both cases yielded results which are congruent with observations and monitoring data. The results presented in this work undoubtedly indicate that hazard assessment for the island of Stromboli should take into account the fact that a new magma intrusion could lead to further destabilisation of the slope, which may be more significant than the one recently observed because it will affect an already disarranged deposit and fractured and loosened crater area. The two-pronged approach based on the analysis of 3D multi-temporal mapping datasets and on the application of LE methods contributed to better understanding volcano flank behaviour and to be prepared to undertake actions aimed at risk mitigation.

New mechanisms for modelling the motion of the human ankle complex

The relevance of human joint models was shown in the literature. In particular, the great importance of models for the joint passive motion simulation (i.e. motion under virtually unloaded conditions) was outlined. They clarify the role played by the principal anatomical structures of the articulation, enhancing the comprehension of surgical treatments, and in particular the design of total ankle replacement and ligament reconstruction. Equivalent rigid link mechanisms proved to be an efficient tool for an accurate simulation of the joint passive motion. This thesis focuses on the ankle complex (i.e. the anatomical structure composed of the tibiotalar and the subtalar joints), which has a considerable role in human locomotion. The lack of interpreting models of this articulation and the poor results of total ankle replacement arthroplasty have strongly suggested devising new mathematical models capable of reproducing the restraining function of each structure of the joint and of replicating the relative motion of the bones which constitute the joint itself. In this contest, novel equivalent mechanisms are proposed for modelling the ankle passive motion. Their geometry is based on the joint’s anatomical structures. In particular, the role of the main ligaments of the articulation is investigated under passive conditions by means of nine 5-5 fully parallel mechanisms. Based on this investigation, a one-DOF spatial mechanism is developed for modelling the passive motion of the lower leg. The model considers many passive structures constituting the articulation, overcoming the limitations of previous models which took into account few anatomical elements of the ankle complex. All the models have been identified from experimental data by means of optimization procedure. Then, the simulated motions have been compared to the experimental one, in order to show the efficiency of the approach and thus to deduce the role of each anatomical structure in the ankle kinematic behavior.

Soil-structure interaction during tunnelling in urban area: observations and 3D numerical modelling

This work illustrates a soil-tunnel-structure interaction study performed by an integrated,geotechnical and structural,approach based on 3D finite element analyses and validated against experimental observations.The study aims at analysing the response of reinforced concrete framed buildings on discrete foundations in interaction with metro lines.It refers to the case of the twin tunnels of the Milan (Italy) metro line 5,recently built in coarse grained materials using EPB machines,for which subsidence measurements collected along ground and building sections during tunnelling were available.Settlements measured under freefield conditions are firstly back interpreted using Gaussian empirical predictions. Then,the in situ measurements’ analysis is extended to include the evolving response of a 9 storey reinforced concrete building while being undercrossed by the metro line.In the finite element study,the soil mechanical behaviour is described using an advanced constitutive model. This latter,when combined with a proper simulation of the excavation process, proves to realistically reproduce the subsidence profiles under free field conditions and to capture the interaction phenomena occurring between the twin tunnels during the excavation. Furthermore, when the numerical model is extended to include the building, schematised in a detailed manner, the results are in good agreement with the monitoring data for different stages of the twin tunnelling. Thus, they indirectly confirm the satisfactory performance of the adopted numerical approach which also allows a direct evaluation of the structural response as an outcome of the analysis. Further analyses are also carried out modelling the building with different levels of detail. The results highlight that, in this case, the simplified approach based on the equivalent plate schematisation is inadequate to capture the real tunnelling induced displacement field. The overall behaviour of the system proves to be mainly influenced by the buried portion of the building which plays an essential role in the interaction mechanism, due to its high stiffness.

A new 3D modelling paradigm for discrete model

Until few years ago, 3D modelling was a topic confined into a professional environment. Nowadays technological innovations, the 3D printer among all, have attracted novice users to this application field. This sudden breakthrough was not supported by adequate software solutions. The 3D editing tools currently available do not assist the non-expert user during the various stages of generation, interaction and manipulation of 3D virtual models. This is mainly due to the current paradigm that is largely supported by two-dimensional input/output devices and strongly affected by obvious geometrical constraints. We have identified three main phases that characterize the creation and management of 3D virtual models. We investigated these directions evaluating and simplifying the classic editing techniques in order to propose more natural and intuitive tools in a pure 3D modelling environment. In particular, we focused on freehand sketch-based modelling to create 3D virtual models, interaction and navigation in a 3D modelling environment and advanced editing tools for free-form deformation and objects composition. To pursuing these goals we wondered how new gesture-based interaction technologies can be successfully employed in a 3D modelling environments, how we could improve the depth perception and the interaction in 3D environments and which operations could be developed to simplify the classical virtual models editing paradigm. Our main aims were to propose a set of solutions with which a common user can realize an idea in a 3D virtual model, drawing in the air just as he would on paper. Moreover, we tried to use gestures and mid-air movements to explore and interact in 3D virtual environment, and we studied simple and effective 3D form transformations. The work was carried out adopting the discrete representation of the models, thanks to its intuitiveness, but especially because it is full of open challenges.

2D and 3D numerical modelling of multilayer detachment folding and salt tectonics

Numerical modelling was performed to study the dynamics of multilayer detachment folding and salt tectonics. In the case of multilayer detachment folding, analytically derived diagrams show several folding modes, half of which are applicable to crustal scale folding. 3D numerical simulations are in agreement with 2D predictions, yet fold interactions result in complex fold patterns. Pre-existing salt diapirs change folding patterns as they localize the initial deformation. If diapir spacing is much smaller than the dominant folding wavelength, diapirs appear in fold synclines or limbs.rnNumerical models of 3D down-building diapirism show that sedimentation rate controls whether diapirs will form and influences the overall patterns of diapirism. Numerical codes were used to retrodeform modelled salt diapirs. Reverse modelling can retrieve the initial geometries of a 2D Rayleigh-Taylor instability with non-linear rheologies. Although intermediate geometries of down-built diapirs are retrieved, forward and reverse modelling solutions deviate. rnFinally, the dynamics of fold-and-thrusts belts formed over a tilted viscous detachment is studied and it is demonstrated that mechanical stratigraphy has an impact on the deformation style, switching from thrust- to folding-dominated. The basal angle of the detachment controls the deformation sequence of the fold-and-thrust belt and results are consistent with critical wedge theory.rn

Il senso di presenza nelle realtà virtuali vissute tramite HMD: l'interazione e le interfacce

Grazie alla crescente evoluzione tecnologica è oggi possibile, tramite Head Mounted Display (HMD), vivere una realtà virtuale ricca nei dettagli, interattiva ed immersiva. L’avanzamento in questo settore ha infatti portato a una vera e propria rivoluzione, aprendo la possibilità di utilizzare questa tecnologia in molteplici ambiti. L’ostacolo riscontrato è che a un progresso di tale entità non si associa un adeguato aggiornamento e perfezionamento riguardo alle metodologie di interazione con oggetti 3D, dell’utilizzo di interfacce grafiche e del generale design ambientale. La diretta conseguenza di questo mancato aggiornamento è quella di indebolire o addirittura annullare l’effetto presenza dell'HMD, requisito indispensabile che consente all’utente di immergersi sensorialmente nel contesto simulato. L’obiettivo di questo studio consiste nel comprendere cosa è necessario tenere in considerazione e quali regole vanno cambiate per poter mantenere un'alta sensazione di presenza per l'utente all’interno di una realtà virtuale. A questo scopo è stato creato un ambiente virtuale 3D in grado di supportare l'utilizzo di un HMD, l'Oculus Rift, e di diversi dispositivi di input in grado di consentire controllo tramite movimenti naturali, il Razer Hydra ed il Leap Motion, in modo da poter effettuare un'analisi diretta sul livello del fattore presenza percepito nell'effettuare diverse interazioni con l'ambiente virtuale e le interfacce grafiche attraverso questi dispositivi. Questa analisi ha portato all'individuazione di molteplici aspetti in queste tipologie di interazioni e di design di intrefacce utente che, pur essendo di uso comune negli ambienti 3D contemporanei, se vissuti in un contesto di realtà virtuale non risultano più funzionali e indeboliscono il senso di presenza percepito dall'utente. Per ognuno di questi aspetti è stata proposta ed implementata una soluzione alternativa (basata su concetti teorici quali Natural Mapping, Diegesis, Affordance, Flow) in grado di risultare funzionale anche in un contesto di realtà virtuale e di garantire una forte sensazione di presenza all'utente. Il risultato finale di questo studio sono quindi nuovi metodi di design di ambienti virtuali per realtà aumentata. Questi metodi hanno permesso la creazione di un ambiente virtuale 3D pensato per essere vissuto tramite HMD dove l'utente è in grado di utilizzare movimenti naturali per interagire con oggetti 3D ed operare interfacce grafiche.

One small scan for radiology, one giant leap for forensic medicine - Post-mortem imaging replaces forensic autopsy in a case of traumatic aortic laceration

The questions of cause and manner of death are the most pressing ones in any forensic investigation. Traditionally, autopsy is the means to provide answers to these questions and despite the increasing use of CT and MR in the post-mortem setting, imaging has usually been an adjunct to forensic autopsy. Here we describe a case where post-mortem CT and MR were performed instead of autopsy, at the request of the responsible public prosecutor. The forensic conclusions derived from imaging, including cause and manner of death were accepted by the legal authorities, thereby setting precedence for future cases. This case represents a landmark in forensic medicine and is another step toward the full realization of minimally invasive forensic autopsy.

Combining 3D tracking and surgical instrumentation to determine the stiffness of spinal motion segments: a validation study

The spine is a complex structure that provides motion in three directions: flexion and extension, lateral bending and axial rotation. So far, the investigation of the mechanical and kinematic behavior of the basic unit of the spine, a motion segment, is predominantly a domain of in vitro experiments on spinal loading simulators. Most existing approaches to measure spinal stiffness intraoperatively in an in vivo environment use a distractor. However, these concepts usually assume a planar loading and motion. The objective of our study was to develop and validate an apparatus, that allows to perform intraoperative in vivo measurements to determine both the applied force and the resulting motion in three dimensional space. The proposed setup combines force measurement with an instrumented distractor and motion tracking with an optoelectronic system. As the orientation of the applied force and the three dimensional motion is known, not only force-displacement, but also moment-angle relations could be determined. The validation was performed using three cadaveric lumbar ovine spines. The lateral bending stiffness of two motion segments per specimen was determined with the proposed concept and compared with the stiffness acquired on a spinal loading simulator which was considered to be gold standard. The mean values of the stiffness computed with the proposed concept were within a range of ±15% compared to data obtained with the spinal loading simulator under applied loads of less than 5 Nm.