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Inria / Raweb 2004
Team: i3D

Team : i3d

Section: New Results


Two-Finger Haptic Interactions for Scientific Visualisation

Participants : Tangui Morvan, Sabine Coquillart.

One of the main problems of scientific visualisation lies in the visualisation of multiple simultaneous information. It can occur when trying to visualise the divergence or curl of a vector field on top of its representation, or when visualizing complex multivariate data such as tensor fields.... Such complex information often leads to visual clutter. Adding haptics to the visualisation can be a good way to tackle this problem.

One of the particularities of the Spidar haptic device [20] is its reconfigurability, with an 8-motor configuration it is for example possible to have 3 Dof haptic feedback on two fingers. This configuration provides an additional information compared to traditional one point configurations: the information of thickness between the two fingers.

Several interaction techniques have been developed under Amira to take advantage of this additional haptic information in order to visualise multiple or complex data [20]. These techniques consist in the haptic representation of classical vector and tensor field visualisation primitives: streamlines, streamtubes and hyper-streamlines. For each of these primitives a visual representation was first developed under Amira, a haptic representation was then added on top of it.

Streamlines are one of the most basic stream primitives. They represent the trajectory of a massless particle in a vector field. Their haptic representation is well-known and consists in constraining one of the fingers on the line, with what is called a virtual fixture.

Streamtubes are an extension of streamlines: they are obtained by sweeping a circular cross-section, with a radius proportional to the divergence, along the streamline. The divergence can then be seen as an additional thickness information on top of the streamline. The haptic representation is then straightforward: one finger is constrained on the streamline while the other collides with the cross-section. This way, the divergence is felt by the user as the thickness between its two fingers (see Figure 8).

Figure 8. Haptic exploration of a streamtube in flow data under Amira on the Stringed Haptic Workbench (Geobench project, data ©CEA-DAM)
two-fingers-rwb

Hyper-streamlines are the extension of streamlines to symmetric second-order tensor fields. They are obtained by sweeping an elliptic cross-section whose axis correspond to the minor and medium eigenvectors along the streamlines of the major eigenvectors. They bear some similarities with streamtubes, their haptic representation is thus also quite similar to that of the streamtubes. One finger is constrained around the streamline while the other collides with the elliptic cross-section. The user can then feel the 3 eigenvectors simultaneously.


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