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Computer models and simulation software (Software)

The POEMS project has developed and utilized two types of visual computer models: One type consists of complete geometrical models, where users can navigate around and explore the virtual environment in real time using different input devices (e.g. joystick, buttons, VR-bike etc.). The second type are 360° panoramic photographs, or 'roundshots' of real places. The roundshot models were created by wrapping the 360° roundshots onto a virtual cylinder. This creates an undistorted view for the observer positioned in the centre of the cylinder. Roundshot models have very high graphical fidelity while model complexity is small (typically 1200 polygons with 25MB textures), so they do not demand high computational power. They are well suited for experiments where only rotational motions are applied.

There exist several roundshot models, both from open spaces (e.g. Tübingen Market Place) or interior rooms (e.g. Motion Lab at the Max Planck Institute). On the other hand, complete geometrical models are much more complex: Virtual Tübingen for example consists of about 80.000 polygons and 1 GB textures, and thus requires high performance computers for the experiments. The advantage is that they allow for unrestricted large space navigation, with any kind of motion (translation, rotation, roll, pitch etc.).

Roundshot models and visual geometrical models have acoustic counterparts in the POEMS models database; HeadScape and Binscape models. These models in turn originate from CATT-Acoustic GEO models. A HeadScape model is created by simulating 128 different binaural room impulse responses (BRIRs, in Lake SIM format) corresponding to different orientations of the listener's head in a CATT-Acoustic model. User interaction (head / camera rotation) is then enabled by the Lake DSP hardware HeadScape convolver tool. As only rotational motion is allowed, this model format will be used in conjunction with the visual roundshot models.

HeadScape simulations have very high acoustic fidelity but as they are restricted to rotational motion, we need another type of format to complement the complete visual geometrical models. For this purpose, BinScape models, consisting of GEO-files for early reflection calculation and SIM-files for late reverberation rendering, will be used. As only the early parts of the BRIR (the direct sound + the 1st early reflections) are updated in real time, the fidelity of these models is lower than HeadScape models but on the other hand they allow any kind of motion.

When full user interaction is not required or when it is necessary to have very high fidelity acoustic simulations, e.g. in some of the basic experiments and pilot studies, acoustic walkthroughs can also be rendered offline directly in CATT-Acoustic by using the 'Walkthrough convolver'.

Means to run these models are provided by the veLib and the HRTF aquisition software and system. The veLib is a software library developed by MPI to meet the requirements of the psychophysical experiments conducted within POEMS. In order to display VR models on a given computer hardware, we need to have the programs that interpret the user's input and provide the appropriate output for the given situation. This simplified description fits most VE/VR applications.

However, the overall similarity between different applications can be summarized in a software library, which provides most common features. Many different VR software libraries and packages are publicly available on the Internet or professionally sold by companies. To our knowledge, however, none of them combines all the specific needs of our experiments. This was the reason to develop a library on our own that meets those requirements. Most important of all, we have required a very high degree of control of timing and usage of simplifying features for our psychophysical experiments.

The HRTF aquisition system and software was developed for the purpose of investigating the importance of idiosyncratic head-related auditory cues in acoustic motion simulation. HRTFs (Head Related Transfer Functions) are an integral part of many virtual acoustic engines today; however, the importance of using personalized HRTFs is rather unclear for motion simulation scenarios.

The system consists of:
- 32 loudspeakers;
- 3.2m high loudspeaker stand of stainless steel to hold the array;
- 1 chair for test person support;
- 2 microphones ;
- 1 microphone holder;
- 1 laser pointer;
- 1 PC computer with sound card;
- 1 audio power amplifier;
- 1 stereo microphone preamplifier;
- 1 loudspeaker 32-channel multiplexer;
- Dedicated software developed by the Chalmers group for this project.

A main goal was to design the system to measure as fast as possible, since previous systems for acquiring HRTFs have been rather time consuming and would have made the experimental process ineffective.

Informations connexes

Reported by

Applied Acoustics, Chalmers University of Technology
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