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Dynamic Deformation Using Adaptable, Linked Asynchronous FEM Regions
Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology. (NVIS)
Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology. (NVIS)ORCID iD: 0000-0003-2429-0842
Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology. (NVIS)
2009 (English)In: Spring Conference on Computer Graphics / [ed] Helwig Hauser and Stephen N. Spencer, New York: ACM , 2009, 197-204 p.Conference paper (Refereed)
Abstract [en]

In order to simulate both physically and visually realistic soft tissue deformations, the Finite Element Method (FEM) is the mostpopular choice in the literature. However it is non-trivial to modelcomplex behaviour of soft tissue with sufficient refresh rates, especiallyfor haptic force feedback which requires an update rate ofthe order of 1 kHz. In this study the use of asynchronous regions isproposed to speed up the solution of FEM equations in real-time. Inthis way it is possible to solve the local neighborhood of the contactwith high refresh rates, while evaluating the more distant regions atlower frequencies, saving computational power to model complexbehaviour within the contact area. Solution of the different regionsusing different methods is also possible. To attain maximum efficiencythe size of the regions can be changed, in real-time, in responseto the size of the deformation.

Place, publisher, year, edition, pages
New York: ACM , 2009. 197-204 p.
Keyword [en]
Finite Element Method, surgery simulations, haptics
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-18053DOI: 10.1145/1980462.1980500ISBN: 978-1-4503-0769-7OAI: diva2:214148
SCCG '09 Spring Conference on Computer Graphics, April 23-25, Budmerice, Slovakia
Available from: 2009-06-08 Created: 2009-05-04 Last updated: 2014-10-08Bibliographically approved
In thesis
1. Haptic Interaction with Deformable Objects
Open this publication in new window or tab >>Haptic Interaction with Deformable Objects
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The integration of haptics into virtual environments has triggered a new era by allowing interaction with virtual objects through force feedback in a number of fields. Medicine has been the field with highest potential benefit through improved realism and immersion. Not only have virtual environments become superior to traditional medical training methods due to cost-efficiency, repeatability, and objective assessment but the idea of surgery rehearsal by using patient specific data has been raised as well.

Achieving sufficient realism in haptics has been a significant challenge due to performance requirements. In order to provide a stable and smooth feedback to the user, the update rates of force feedback need to be in the range of 1~kHz, which restricts the solution time for real-time interactive applications. Realism, on the other hand, demands advanced algorithms capable of simulating physical properties. These advanced algorithms have a high computational burden, taking significant amounts of time and their real-time use, therefore, mostly requires simplification of the virtual scene affecting realism.

During palpation, information is transferred to the hand from the local neighbourhood of contact. In deformation simulations, it is therefore common to use a multiresolution scheme, where the local region is modelled with a higher resolution than more distant regions, and at higher update rates. This approach saves computational power, however the less elaborate modelling in the more remote regions affects accuracy. This thesis presents a pipeline to analyse the error introduced by multiresolution techniques. The idea is to estimate how simulation parameters lead to different error magnitudes, as a preprocessing step. This information can subsequently be used for monitoring the error in real-time, or for adjusting simulation parameters to keep the error under a desired limit.

There is a trade-off between accuracy/error and computation time required. In an ideal situation, this error should be kept under perceivable levels. Levels of perception is a topic that has been surveyed in psychophysics among other aspects of touch. It has been shown that differences smaller than a ratio of a reference signal, such as force or stiffness, cannot be perceived. Evaluating the exact value of this ratio, however, is nontrivial since there are many secondary factors having a significant impact, such as the multimodal input. This thesis presents the analysis of some factors affecting the sense of touch that were shown to have such impact. Effects of exploratory procedures on stiffness perception were examined through user studies, followed by another study indicating the significant effects of stiffness gradient.

Medical data, such as MR and CT, has much higher resolution than is practically used for deformable meshes. It has been common practice to model deformation behaviour by a mesh with lower resolution than is used for visual representation. Lastly, this thesis presents an approach to introduce high-resolution information. The proposed algorithm allows for the detection of inhomogeneous structures beneath a surface. This can be applied in situations similar to the diagnosis of tumours by palpation. The approach is independent of mesh structure and resolution, and can be integrated into any proxybased haptic rendering algorithm. This makes the algorithm a complementary choice for deformation simulation.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 72 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1522
National Category
Engineering and Technology
urn:nbn:se:liu:diva-92804 (URN)978-91-7519-615-2 (ISBN)
Public defence
2013-06-05, Domteatern, Visualiseringscenter C, Kungsgatan 54, 602 33 Norrköping, 09:15 (English)
Available from: 2013-05-22 Created: 2013-05-22 Last updated: 2014-10-08Bibliographically approved

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