The ESF-funded junior research group VICCI dealt from 2012 until the end of 2014 with the development, control and integration of cyber physical systems (CPS) at the Faculty of Computer Science of the Dresden University of Technology. The scope includes smart home environments and supporting people in the ambient assisted living.

Today, I am writing about Visualization in heterogeneous and distributed infrastructure. Well, this sounds more advanced than it is. Is simply is about remote visualization.

A first prototype for compressed video transfer was successfully integrated in a collaboration project with the HZDR Dresden by a co-advised student project. This work was presented on the international conferences SuperComputing 2013 (Denver) and 2014 (New Orleans). Both presentations focused on the PIConGPU research project by the HZDR, was an ACM Gordon Bell Finalist at the SC2013. This shows the clear applicability of our approach.

The video transfer, being the crucial part of the whole approach, was extended by multiple different compression techniques. In addition and worth a special mention is the bachelor thesis of Christoph Träger, which aimed at latency masking via image interpolation and extrapolation at the displaying thin client.

ba_traeger_idee

The core idea is latency masking via image interpolation on the display device. Based on the original image (left) the target image (center) is approximated. Re-projection of the image data allows for this approximation (right).

The prototypical software component for the video transfer is called RIV. The current state of the project can be downloaded from the VICCI website.

The implementation of the image interpolation for latency masking can be downloaded from the website of the bachelor thesis of Christoph Träger. Important: all rights on that source code remain with Christoph Träger! The source code presented there may only be used for teaching and research. Any further use requires the consent of the original author. The TU Dresden has the right for additional use of the source code.

 

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The ESF-funded junior research group VICCI dealt from 2012 until the end of 2014 with the development, control and integration of cyber physical systems (CPS) at the Faculty of Computer Science of the Dresden University of Technology. The scope includes smart home environments and supporting people in the ambient assisted living.

My work package for visualization and visual analysis has within the project investigated three essential aspects and corresponding solutions:

  • visual analysis of complex, multi-dimensional, multimodal, dynamic space-time data,
  • visualization in heterogeneous, mobile and distributed IT infrastructure, and
  • implementation of visualization systems and components.

Today I am writing about the visual analysis of complex space-time data.

teaser

Visual analysis serves as administrative overview of a current CPS, mainly for security reasons, as assistance during development, and the operation of the system. Particularly interesting are out-of-the-ordinary (erroneous) behavior and the formation of emergent system properties. For this a visual exploration with minimal previous assumptions is necessary. For example, certain data, like forces acting upon joints of a robot arm, be visualized more effectively by representations in geometrical context. This assumption however reduced the generality of visualization.

I thus developed a corresponding visualization of data collected by the CPS using coordinated views of continuous-time scatter plots, continuous-time parallel coordinate plots and temporal heatmaps. This application is capable of interactive real-time representation of generic multi-dimensional data and offers the means for a visual analysis. The developed system was published in the journal Computer Graphics Forum, the leading European Journal on Visualization. In the context of the evaluation, live data from our laboratory CPS war visualized, presented and discussed with a broad audience.

  • [DOI] S. Grottel, J. Heinrich, D. Weiskopf, and S. Gumhold, “Visual Analysis of Trajectories in Multi-Dimensional State Spaces,” Computer Graphics Forum, vol. 33, iss. 6, pp. 310-321, 2014.
    [Bibtex]
    @article {Grottel2014HDTraj,
      author = {Grottel, Sebastian and Heinrich, Julian and Weiskopf, Daniel and Gumhold, Stefan},
      title = {{Visual Analysis of Trajectories in Multi-Dimensional State Spaces}},
      year = {2014},
      journal = {Computer Graphics Forum},
    volume = {33},
    number = {6},
    pages = {310--321},
      doi = {10.1111/cgf.12352}
    }

DOI: 10.1111/cgf.12352

This visualization was implemented as a plugin for the MegaMol visualization system. The source code can be downloaded freely and can be used according to the enclosed License:

hdtraj.mmplugin.ziphdtraj.mmplugin.zip Multi-Dimensional Trajectory Visualization MegaMol Plugin
[99.7 KB; MD5: 0a6eaf465318b0f256ecfdf8a8b4ad50; More Info]

To compile the MegaMol system and the plugin, use the appropriate Instructions on the MegaMol website.

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I like working with Software. I have fun handling large data sets and producing interactive 3D visualizations which are useful, nice and cool. On the way to create them I, of course, need a huge lot of functions, libraries and services. It is a painful fight till all those parts fit nicely together. But, I would be lying if I would say that this fight is not part of the fun. It is great seeing the parts from different persons matching together to a working whole. In my current projects source code combines from colleagues from Dresden, ex-colleagues from Stuttgart, my student assistants and my advised students.

However, the real pain are the interfaces and the stability of those parts. Of course, you could swap the implementation of anything behind a good interfaces without influencing the rest of the system. But, someone needs to show me a good interface, yet! I haven’t seen one without its problems, and I have seen many. The continuous development get increasingly difficult with each component added. Especially if there is no overseeing architect.

MegaMol-Highlevel-ArchitectureAs a matter of fact, MegaMol is currently exactly on that way down. It is actively used in Stuttgart and Dresden. I, of course, want to foster and extend that process. After all, MegaMol is my project and I am proud of it. But, the larger it gets and the more it is used, the harder it gets to continue the development. Several fundamental problems can only be solved with fundamental changes. These will bring displeasure. And I am not sure how to handle the necessary work load. On the one hand I am reducing my active development to act more like a director of the future development. On the other hand, the actual development is passed from one Ph.D. student to the next, like a scapegoat. This, of course, does not help. I am really not sure how to solve this.

configurator2MegaMol Modul Graph (10.1109/TVCG.2012.282)

But, I have my plans. “Partitioning”! And I know exactly which parts need to have my priority and which are critical. The main problems, however, are the interfaces in between. Those are far from being clean and therefore the whole current partitioning is in vain. The first tries to solve that were … semi-successful. But, I don’t even think of quitting!

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My work nicely accelerates and my projects evolve as expected. Ok, maybe they evolve a bit slower than I would like it, but I can be satisfied.

As part of the whole development I finally updated my research profile here on my own website. Soon there will be news on my research and my current projects.

Last week was full of work. Somehow, I write something like this every week. Well…

Together with two colleagues I worked on a submission for a conference last week. A nice paper about a visualization technology. Of course, I cannot say more about it as long as it is not accepted for publication yet. We will see. We did a good job and I am confident. Well, I was confident with most papers that got rejected too. Whatever.

Additionally, there was good news last week. The paper of another colleague of mine, with which I was involved, was accepted for publication at the Multimedia Modelling 2015:

  • [DOI] M. Spehr, S. Grottel, and S. Gumhold, “Wifbs: A Web-based Image Feature Benchmark System,” in MultiMedia Modeling – 21th Anniversary International Conference, MMM 2015, Sydney, Australia, January 5-7, 2015, Proceedings, 2015, pp. 159-170.
    [Bibtex]
    @inproceedings{spehr2015mmm,
      author    = {Marcel Spehr and
                   Sebastian Grottel and
                   Stefan Gumhold},
      title     = {Wifbs: A Web-based Image Feature Benchmark System},
      booktitle = {MultiMedia Modeling - 21th Anniversary International Conference, {MMM} 2015, Sydney, Australia, January 5-7, 2015, Proceedings},
      editors   = {Xiangjian He, Suhuai Luo et al.},
      year      = {2015},
      pages     = {159--170},
      doi       = {10.1007/978-3-319-04114-8_2},
    }

I don’t want to take credit for other’s achievements. The idea, the implementation, the system and the publication, all of that was mostly the work of my colleague Marcel Spher. Great work. All I did was helping out with some details, pointing in some directions and helping with writing the paper itself.

I like system papers. It is work beyond simple software used in research. These system, the one presented here and my MegaMol, have the potential to stay useful for a long time.

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Today, I am only writing a short note on MegaMol.

We have done it! We published the MegaMol system as systems paper:

  • [DOI] S. Grottel, M. Krone, C. Müller, G. Reina, and T. Ertl, “MegaMol — A Prototyping Framework for Particle-based Visualization,” Visualization and Computer Graphics, IEEE Transactions on, vol. 21, iss. 2, pp. 201-214, 2015.
    [Bibtex]
    @article{grottel2014megamol,
        author={Grottel, S. and Krone, M. and M\"{u}ller, C. and Reina, G. and Ertl, T.},
        journal={Visualization and Computer Graphics, IEEE Transactions on},
        title={MegaMol -- A Prototyping Framework for Particle-based Visualization},
        year={2015},
        month={2},
        volume={21},
        number={2},
        pages={201--214},
        keywords={Data models;Data visualization;Graphics processing units;Libraries;Rendering (computer graphics);Visualization},
        doi={10.1109/TVCG.2014.2350479},
        ISSN={1077-2626}
    }

Doi: 10.1109/TVCG.2014.2350479

All the hard work really paid off. MegaMol has now been published in the IEEE Journal “Transactions on Visualization and Computer Graphics”, in short TVCG. That is the top journal of the visualization community. I have to admit, I am pretty proud.

And I am curious what will come next. I would like to continue working with MegaMol, and to help to evolve the software even further. But, of course, this depends on my future employment. MegaMol has such a potential. *sigh*

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Today I want to talk about one of my newest published research papers, about visualization of multi-dimensional trajectories. It is electronically available here at the Wiley Online Library (http://onlinelibrary.wiley.com/doi/10.1111/cgf.12352/abstract): Visual Analysis of Trajectories in Multi-Dimensional State Spaces [1].

First off, what is multi-dimensional trajectory? We were investigating the state of complex systems, like automation system or robotics. Each element of such a system, e.g. a robotic motor or a sensor, holds several state variables, like sensed temperature or rotation moment applied by the motor. These variables might even be vectors. But even if they are only scalar values, the system is constituted from several dozens of such elements. Thus, the state of the whole system is always a vector containing the state variables of all components. For the systems we investigated, these vectors are of the size of severs tens or variables. This order or magnitude is referred to by the term multi-dimensional, compared to high-dimensional, which refers to data with several hundred or thousand dimensions. The whole system state can be understood as point in the multi-dimensional state space. Now, our system is not static, but is monitored in real time. Thus the values of the state variables change. Temperatures rise and motors move. This can be interpreted as the point of the system state moving through the state space. This movement path is what we call the trajectory.

md_trajectory_teaser

Our approach on visualizing this trajectory was using classical visualization metaphors on multi-dimensional data visualization, namely scatterplot matrices and parallel coordinate plots. We supplemented these plots with additional views, like a temporal heat map. The main aspect of our work was the technique we used to generate these plots. Normally, the sample points of the data will be simply drawn into the plots as points or poly-lines. We, however, took the nature of the data into account, which is the temporal continuity of the discretely sampled signal. We constructed an integration concept for continuous plots in this respect. Our work was based on previous work on continuous scatterplots and parallel coordinate plots, which used spatially continuous interpolation. We adapted this concept to continuous-time interpolation.

 md_trajectory_compare

[1] [doi] S. Grottel, J. Heinrich, D. Weiskopf, and S. Gumhold, “Visual Analysis of Trajectories in Multi-Dimensional State Spaces,” Computer Graphics Forum, vol. 33, iss. 6, pp. 310-321, 2014.
[Bibtex]
@article {Grottel2014HDTraj,
  author = {Grottel, Sebastian and Heinrich, Julian and Weiskopf, Daniel and Gumhold, Stefan},
  title = {{Visual Analysis of Trajectories in Multi-Dimensional State Spaces}},
  year = {2014},
  journal = {Computer Graphics Forum},
volume = {33},
number = {6},
pages = {310--321},
  doi = {10.1111/cgf.12352}
}
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Data set file formats are a real running gag in the context of scientific visualization. Often the file formats are rather useless and there often are no established standards. Most of the time ASCII-text files greet you as the results for simulations. These are large, bulky and a pain to parse.

With MegaMol™ we tries to tackle this problem several times, with limited success I have to say. We nicely extended the list of file formats we need to be able to load due to our project partners with a whole bunch of file formats of our own. These, however, have proven themselves to be similar useless in the long run. This year the need for a solution to efficiently load larger data (not yet big data) arose, once again. The best way we found was the MMPLD file format. It basically is a binary memory dump of the simplest data structure MegaMol has to offer.

What can I say? It works. Of course this is no solution with sustainability or scalability. The huge number of failed attempts to create a good file format raises the questions if such a file format can be defined at all. I don’t want to abandon hope. We—CGV-TUD, VISUS, HLRS, ThEt-PB, SCCS TUM, and TLD-KL—at least agreed that we all have this problem, and that we all are interested in a solution. We will see…

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