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GeoWall - Interactive 3D Visualisation

Overview

Wavefield of 1999 Fiji earthquake

Animation of wavefield generated by the
1999 Fiji earthquake (B. Schuberth)

Numerical models are of constantly growing importance in the Geosciences. Due to increased computing power and improved algorithmics such models tend to deliver an ever increasing amount of data. However, as Richard Hamming put it “the purpose of computing is insight, not numbers!”. Thus, the visualisation of the obtained results plays a crucial role.

Many simulations at Munich Geophysics center around convection in the Earth's mantle and seismic wave propagation. An intuitive understanding of the related structures in the deep interior of the Earth is best achieved by 3D visualisations.

A useful tool for 3D visualisation of large data-sets must be efficient, interactive and allow intuitive usage. Combining the VTK-based visualisation tool ParaView with the computational power of our TETHYS cluster and a low-budget technique for stereoscopic 3D projection provides such a technical commodity.

Concept of Stereoscopic 3D Projection

GeoWall in use

GeoWall in use

Three-dimensional viewing requires that the eyes see the object from slightly different points of view. This can be simulated by sending different images to the eyes, either with little screens or glasses with mirrors/prisms that show individual pictures to each eye, or by showing both pictures on the same screen with filtering glasses. The latter method is suited for a larger audience because one single screen suffices for all viewers. Different filtering techniques are possible, like e.g. shutter glasses, colour filters or polarising filters. GeoWalls typically employ the latter approach. This technique combines full colour pictures with cheap passive glasses, but requires a screen setup that can display pictures with polarised light. More information can e.g. be found at the GeoWall Consortium.

Common to all 3D projection methods is that the spectators get only a 3D view of the scene, but the picture itself is still flat. This demands for interactivity, if the spectator cannot change his/her position relative to the object, the displayed object must be free to move. Hence, static 3D picture viewers are not very useful. Interactive software is necessary, or at least precomputed animations.

Hardware Setup

The GeoWall operated by the GeoComputing Group Munich consists of the following components:

Setup of the beamers and polarisation glasses

Setup of the two beamers and the
polarisation glasses

  • Linux-PC with an Nvidia Quadro FX 4600 graphics card. This is a dual-head graphics card able to operate in clone-mode.
  • two NEC LT245 DLP projectors operating at 1024×768 resolution. DLP stands for Digital Light Processing, a technique where the brightness of individual pixels is controlled by pulse-width modulated mirror tilting frequency. Note that standard LCD projectors are not feasible, since the projectors themselves must not emit polarised light.
  • linear polarising filters (for the projectors and the viewers' glasses)
  • projection screen made of silver screen fabric by Vision24. Reflection on most screens polarises the light, thus, destroying the intended 3D effect. This fabric is an inexpensive alternative to full metal screens.

Software Setup

Of the different features ParaView offers as a visualisation tool, the one that was key for choosing it, was its flexible architecture which allows to run it on the very same computing cluster where our simulations are carried out. Thus, it allows to process the resulting large datasets.

  • In Paraview's abstraction concept the cluster functions as data server which stores the data and computes filter operation on them,
  • while the frontend PC functions as render server (computes the polygonal representation) and client (provides the graphical user interface).
by Marcus Mohr last modified 03. Nov 2011 11:05
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Printed 31. Mar 2020 14:31