In-Situ PBVR
(In-Situ Particle Based Volume Rendering)

In-Situ PBVR v1.1 (April 28, 2021)

The latest version of In-Situ PBVR v1.1 is available.
In this v1.1, the GUI of the PBVR client running on the user's PC has been updated from OpenGL to Qt.

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Purpose and outline of program development

As the performance of supercomputers has improved, computing power has increased from tera-scale to peta-scale to exa-scale. Visualization is an essential technology for gaining scientific knowledge from the data generated in simulations. However applying conventional visualization strategies for exa-scale data is difficult with current infrastructure, as network speeds are limited for transferring data to client PCs, as is the RAM and storage available on the clients.

For peta-scale simulations, a client / server visualization protocol is emphasized, where data generated on servers with abundant computing resources are transferred to clients for visualization. However there is concern that data output to client storage itself will be a major bottleneck for exa-scale computing.

In-situ visualization, whereby images are generated on the same environment as the simulations, is a method that is expected to provide efficient visualization for exa-scale simulations. However, conventional in-situ visualization has the following problems.

1.Visualization failures often occur because visualization parameters such as viewpoint position, color and opacity are set before batch processing.
2.The cost of visualization processes suppresses simulation performance as domain decomposition for stencil calculations causes data reconstruction, or because global communications are required.
3.Techniques for visualizing multivariate data from multiphysics simulations are insufficient.

The interactive In-Situ Visualization Framework (In-Situ PBVR), based on the Particle-Based Volume Rendering (PBVR) technique, solves the above problems and can be used to visualize large-scale calculation results obtained from exa-scale simulations.

1.In-Situ PBVR compresses large volume simulation data in to small visualization particle data in the in-situ environment and then transfers the particle data to the client PC for remote interactive visualization. Interactive changes of visualization parameters are made possible by exchanging data between the client and server via a daemon process.
2.The visualization process can be parallelized without changing the domain decomposition, and high scalability can be achieved because it does not require expensive inter-node communication.
3.In-Situ PBVR implements a multivariate visualization function that can be used for various simulations. The function enables composition of volume data and composition of color/opacity functions using user specified algebraic expressions. The computational algebraic system enables multivariate visualization during the simulation runtime.

Program features

・The framework consists of a particle sampler coupled to the simulation code, a daemon that controls interactions by processing files on storage, and a PBVR client that renders visualization results and allows interactive editing on the client PC.

・In addition to a hybrid MPI / OpenMP programming model, the code supports SIMD operations used in the latest many core architectures.

・By inserting a particle generation function into the simulation code, the particle sampler performs visualization processing simultaneously with the batch process of the simulation.

・An ssh port forward connection between the daemon and the PBVR client enables interactive visualization of simulation results during batch process execution.

・Structured grids, unstructured grids (hexahedron) and hierarchical grids (Block Structured AMR) are supported as simulation grids.

・An advanced transfer function design visualizes not only volume rendering but isosurface, cross section and multivariate data.

≪In-Situ PBVR framework≫
In-Situ PBVR framework
≪Synthesis of volume data and transfer function for multivariate analysis≫
Synthesis of volume data and transfer function for multivariate analysis
≪Calculation performance on the supercomputer Oakforest-Packs equipped with Xeon Phi7250≫
A strong scaling test of In-situ PBVR was performed connected to a thermal flow analysis code of about 100 million grids.
Calculation performance on the supercomputer Oakforest-Packs equipped with Xeon Phi7250. A strong scaling test of In-situ PBVR was performed connected to a thermal flow analysis code of about 100 million grids.
≪Comparison of overall performance with traditional visualization apps≫
Network bandwidth is ~11 MB / sec. Visualization was 30 times faster with In-Situ PBVR.

In-Situ PBVR

ParaView

Data size [MB]

581

5144

Particle generation [sec/step]

38

-

Transfer [sec/step]

52

456

Image production [sec/step]

7.7

900

≪Visualization results of heat flow analysis.(Left:In-Situ PBVR、Right:ParaView)≫
In-Situ PBVR gave equivalent results to the conventional visualization app.
Visualization results of heat flow analysis.(Left:In-Situ PBVR、Right:ParaView)In-Situ PBVR gave equivalent results to the conventional visualization app.

Reference

[1] T. Kawamura, T. Noda, Y. Idomura, “Performance Evaluation of Runtime Data Exploration Framework based on In-Situ Particle Based Volume Rendering”, Journal of Supercomputing Frontiers and Innovations, Vol 4, No. 3, pp. 43-54, 2017.
[2] T. Kawamura, Y. Idomura, H. Miyamura, H. Takemiya, “Algebraic Design of Multi-dimensional Transfer Function Using Transfer Function Synthesizer,” Journal of Visualization, Vol.20, No. 1, pp.151-162, DOI 10.1007/s12650-016-0387-1, 2016.
[3] T. Kawamura, T. Noda, Y. Idomura, “In-Situ Visual Exploration of Multivariate Volume Data based on Particle Based Volume Rendering,” Proceedings of ISAV2016 in SC16, ACM Digital Library and IEEE Xplore, pp.18-22, DOI 10.1109/ISAV.2016.9, 2016.

Developer

Computer Science Research and Development Office, Center for Computational Science & e-Systems, Japan Atomic Energy Agency

Contact

ccse-quad(at)ml.jaea.go.jp
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