Rahul Gopal Chaudhari

University of Technology Munich, München, Bavaria, Germany

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Publications (14)15 Total impact

  • Proceedings of the 20th ACM international conference on Multimedia; 01/2012
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    ABSTRACT: For realtime teleoperation with haptic feedback, network-induced artifacts like delay, packet loss and lossy coding of haptic data deteriorate the operability of the system. We provide a systematic quantification of the limits within which, these network-induced degradations are tolerable for human task performance in executing a given haptic task. These limits are conservative in the sense that we do not account for any stabilizing approaches from control engineering to counter the impact of the network-induced degradations. Through experimental evaluation with a pursuit tracking task, we show that task performance is most affected by delay on the network and a strong lossy coding scheme. With statistical analysis we show that task performance is significantly decreased for one-way delay higher than 14 ms and strong lossy coding with a deadband parameter higher than 27%. For the given task, packet loss is found not to affect task performance significantly.
    Haptic Audio Visual Environments and Games (HAVE), 2011 IEEE International Workshop on; 11/2011
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    ABSTRACT: Haptic data reduction schemes address the high packet-rate requirements of networked haptics. Perception-driven predictive coding approaches enable strong packet rate reduction while keeping the introduced distortion below human haptic perception thresholds. The performance of predictive coding is strongly influenced by factors such as human behavior, system characteristics, geometric and impedance properties of the environment, etc. In this paper, we first describe a novel surface geometry-based prediction approach for haptic data reduction where local object surface features are approximated with the help of simple geometric models. Secondly, we present a hybrid framework that combines signal-based and geometry-based prediction. Psychophysical experiments are performed to validate this framework. The results of the proposed geometry-based prediction show an improvement in haptic data reduction of about 54% as compared to the signal-based prediction (linear predictor). Furthermore, the presented hybrid prediction technique allows for an additional gain of 15%.
    Proceedings of the IEEE International Symposium on Haptic Audio Visual Environments and Games; 10/2011
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    Fernanda Brandi, Rahul Gopal Chaudhari, Eckehard G. Steinbach
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    ABSTRACT: Recently proposed haptic offline compression algorithms remove perceptually irrelevant haptic samples to achieve data reduction. At display-time, the irregularly subsampled haptic signal is resampled at a higher constant sampling rate using interpolation. Such algorithms, however, have an important drawback. Although they are well suited for large-amplitude quasi-static feedback forces, low-amplitude high-frequency texture information is adversely affected. This informative tactile high-frequency component, critical to convey convincing realistic haptic impressions, needs to be treated separately for compression. To this end, we extract important tactile elements crucial to texture perception from the haptic signal in the time domain and propose a method to encode them so that the overall storage requirements are minimized. We then synthesize and superimpose them onto the reconstructed signal at display-time. Psychophysical tests confirm that the proposed approach significantly improves the texture assessment quality during playback, while reducing storage space requirements by up to 97%.
    IEEE Int. Conference on Virtual Environments, Human-Computer Interfaces and Measurement Systems (VECIMS), Ottawa, ON, Canada; 09/2011
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    R. Chaudhari, E. Steinbach, S. Hirche
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    ABSTRACT: High packet rates in telepresence and teleaction systems pose grave challenges to teleoperation over existing communication infrastructure like the Internet. To counter these issues, efficient perceptually motivated packet-rate reduction schemes have been developed. These schemes are conventionally evaluated for perceived quality via subjective user tests. Such tests are time-consuming, expensive and require precise control of experimental conditions. Computer modeling of telepresence sessions can, on the other hand, bring repeatability, ease of observation, definite control over system parameters and task description and fairness of comparison. In this paper, we present first steps towards a methodology and a framework to model and simulate a networked haptic interaction and evaluate it objectively for the quality of experience. Towards this purpose, we model the human control action and haptic perception process in teleoperation. Our results show that simulations of these models for a range of data reduction scheme parameters produce quality estimates whose trend is comparable to carefully performed subjective user tests.
    World Haptics Conference (WHC), 2011 IEEE; 07/2011
  • J. Kammerl, R. Chaudhari, E. Steinbach
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    ABSTRACT: In cooperative networked virtual environments, haptic rendering enables joint haptic interaction with virtual objects and, thus, shared touch experiences among multiple users. In case of an underlying packet-based communication network (e.g., the Internet), minimizing the end-to-end delay, with the goal of preventing instability of the involved control loops, results in high packet rates. Previously proposed perceptual data reduction approaches address this challenge and satisfy the strict delay constraints. However, significantly increased packet rates still occur during contact events. We present a novel event-based coding scheme based on a distributed haptic-rendering framework that integrates model-based distributed haptic rendering with perceptual data reduction. We also present a comprehensive haptic contact model for signals with multiple degrees of freedom. Furthermore, we show that the integration of event-triggered force transient models from event-based haptics into our local contact model is instrumental for generating convincing haptic feedback. Psychophysical experiments reveal that the approach presented herein allows us to push the data reduction performance beyond what is normally achievable by perceptual data reduction schemes alone while significantly improving the quality of haptic contact feedback.
    IEEE Transactions on Instrumentation and Measurement 02/2011; · 1.36 Impact Factor
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    ABSTRACT: The past decade has witnessed how audio-visual communication has shaped the way humans interact with or through technical systems. In contemporary times, the potential of haptic communication has been recognized as being compelling to further augment human-to-human and human-to-machine interaction. In the context of immersive communication, video and audio compression are considered key enabling technologies for high-quality interaction. In contrast, the compression of haptic data is a field of research that is still relatively young and not fully explored. This disregards the fact that we as humans rely heavily on the haptic modality to interact with our environment. True immersion into a distant environment and efficient collaboration between multiple participants both require the ability to physically interact with objects in the remote environment. With recent advances in virtual reality, man-machine interaction, telerobotics, telepresence, and teleaction, haptic communication is proving instrumental in enabling many novel applications. The goal of this overview article is to summarize the state of the art and the challenges of haptic data compression and communication for telepresence and teleaction.
    IEEE Signal Processing Magazine 02/2011; · 3.37 Impact Factor
  • IEEE Signal Processing Magazine 01/2011; 28(1):87-96. · 3.37 Impact Factor
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    Multimedia Communication Technical Committee (MMTC) E-Letter. 01/2011; 6(1):7-10.
  • Rahul Gopal Chaudhari, Eckehard G. Steinbach, Sandra Hirche
    IEEE World Haptics Conference, WHC 2011, 21-24 June 2011, Istanbul, Turkey; 01/2011
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    ABSTRACT: Audiovisual communications is at the core of multimedia systems that allow users to interact across distances. It is common understanding that both audio and video are required for high-quality interaction. While audiovisual information provides a user with a satisfactory impression of being present in a remote environment, physical interaction and manipulation is not supported. True immersion into a distant environment and efficient distributed collaboration require the ability to physically interact with remote objects and to literally get in touch with other people. Touching and manipulating objects remotely becomes possible if we augment traditional audiovisual communications by the haptic modality. Haptic communications is a relatively young field of research that has the potential to substantially improve human–human and human–machine interaction. In this paper, we discuss the state-of-the-art in haptic communications both from psychophysical and technical points of view. From a human perception point of view, we mainly focus on the multimodal integration of video and haptics and the improved performance that can be achieved when combining them. We also discuss how the human adapts to discrepancies and synchronization errors between different modalities, a research area which is typically referred to as perceptual learning. From a technical perspective, we address perceptual coding of haptic information and the transmission of haptic data streams over resource-constrained and potentially lossy networks in the presence of unpredictable and time-varying communication delays. In this context, we also discuss the need for objective quality metrics for haptic communication. Throughout the paper, we stress the fact that haptic communications is not meant as a replacement of traditional audiovisual communications but rather as an additional dimension for telepresence that will allow us to advance in our quest for truly immersive communication.
    Proceedings of the IEEE 01/2011; · 6.91 Impact Factor
  • Julius Kammerl, Rahul Gopal Chaudhari, Eckehard Steinbach
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    ABSTRACT: Packet-switched communication of haptic data in real-time telemanipulation systems is characterized by high packet rates on the communication channel. Perceptual data reduction techniques for haptic signals successfully address this challenge. By applying a mathematical model of human haptic perception, the transmission of imperceptible signal changes over the network can be avoided. When extending existing haptic data reduction schemes from a single degree of freedom (DoF) to multi-DoFs, the spatial orientation of force feedback vectors acts as an additional perceptual dimension. In this paper, we investigate directional dependencies of haptic data reduction artifacts. Experimental studies reveal that the performance of perceptual data reduction can be significantly improved by adapting the perception thresholds to the spatial direction of force feedback.
    Proceedings of the IEEE International Symposium on Haptic Audio Visual Environments and Games (HAVE ); 10/2010
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    ABSTRACT: Humans interact with their surroundings and other people using multiple perceptual modalities. However, in human-machine-interaction, human-centered computing and modern multimedia systems, we have traditionally concentrated on research into visual and auditory interaction. This is evident from the tremendous advancements that have been achieved so far in digital audio and video technology. More recently, the momentum gained in the areas of 3D audio and 3D video raises significant hope for another quantum leap towards immersive 3D multimedia experiences. The haptic modality and haptic interaction (beyond computer mice, touch screens, etc.) have not received due attention over the past years. This disregards the fact that we rely heavily on the sense of touch in our daily life. True immersion and efficient collaboration between multiple participants both require the ability to physically interact with objects in a shared remote environment. With recent advances in Virtual Reality (VR), Immersive Communication, Telepresence and Telemanipulation, Scientific Visualization, Man-Machine Interaction and Robotics, the demand for richer input and output possibilities is quickly growing. In this context, haptic interaction is rapidly gaining in relevance and is becoming an enabling technology for many novel fields of application. Haptic perception, handled by the human somatosensory system, consists of the kinaesthetic and the tactile sense. Kinaesthetic information refers to the sensation of muscle movements and helps to determine joint positions. Tactile information refers to touch, pressure, temperature, pain, etc. and is a prerequisite for nearly all neuromuscular activities like perception of objects and in case of limited visibility, identification of materials and other surface properties.
  • R. Chaudhari, J. Kammerl, E. Steinbach
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    ABSTRACT: When haptically interacting with virtual rigid bodies, the rendering and display of realistic haptic force-feedback is a challenging task. Conventionally rendered closed-loop proportional feedback forces according to Hooke's law or potential fields impart a feeling of soft contacts and hence are not sufficient to convey the material contact properties of a rigid object. Improvement of haptic contact rendering by incorporating high-frequency transients immediately after contact leads to high packet rates in networked virtual environments (VEs). In this work, we combine event-triggered contact force transients with perceptual coding of haptic signals to achieve a two-fold objective. A significant reduction in data and packet-rates on the network is obtained while improving the realism of interaction with rigid objects, verified by our psychophysical experiments. Furthermore, we describe our observation that the introduction of contact transients serves to mask the artifacts of the perceptual coding scheme to some extent. This allows us to push the data reduction performance beyond what is normally achievable by the haptic compression scheme alone.
    Haptic Audio visual Environments and Games, 2009. HAVE 2009. IEEE International Workshop on; 12/2009