Large-Scale CAD Model Visualization on aScalable Shared-Memory Architecture

Today CAD frameworks are extensively applied in virtually all industrial engineering design projects. Design and development of complete airplanes, ships, cars, etc. is performed on a complete digital basis. In the course of such large scale-engineering projects vast amounts of data are generated, and the complexity of designs is expanding by orders of magnitude.

The problem of how to interpret, understand, and in particular how to interactively visualize these complex designs has grown into an important challenge. With complete geometric databases containing up to billions of primitives the interactive display of the full original data is usually not possible, not even with current state-of-the-art graphics hardware.

Andreas Dietrich¹, Ingo Wald², and Philipp Slusallek¹¹Computer Graphics Group, Saarland University, Saarbrücken, Germany

²Max-Planck-Institut Informatik, Saarbrücken, Germany

Introduction

References

[1] Ingo Wald, Andreas Dietrich, and Philipp Slusallek. An Interactive Out-of Core Rendering Framework for Visualizing Massively Complex Models. In Rendering Techniques 2004, Proceedings of the Eurographics Symposium on Rendering, pages 81–92, 2004.

[2] Andreas Dietrich, Ingo Wald und Philipp Slusallek. Interactive Visualization of Exceptionally Complex Industrial Datasets, ACM SIGGRAPH 2004, Sketches and Applications, 2004.

[3] Ingo Wald. Realtime Ray Tracing and Interactive Global Illumination. PhD thesis, Computer Graphics Group, Saarland University, 2004. Available at http://www.mpisb.mpg.de/~wald/PhD.

Complicated structure:

• Extreme geometric detail all over the model.• Low degree of occlusion.• Complicated geometric topology.• Self-intersecting and overlapping surfaces.• “Soup” of triangles.

Difficult to handle for standard approaches.

Test model dataset:

• Directly exported from original CAD database.• 13,000 object files.• 12 GByte of raw geometrical model data.• Contains more than 350 million triangles.• 20 GByte of data if ray tracing acceleration

structures (k-d trees) are included.

Example: Boeing 777

• Boeing’s first commercial jetliner to be designed fully digital (CATIA framework).• More than 10,000 people involved in 238 geographically dispersed teams.

Shared-Memory Hardware

The complete model including all k-d tree structures is stored in binary form. The binary files can be mapped from (RAM-)disk into the global shared-memory space by the operating system, and are then visible in the virtual address space of each of the 16 client ray tracing processes.

SGI Altix 350:

• 8 nodes each fitted with• 2 Itanium 2 CPUs (1.4 GHz)• 4 GByte local memory

• High-bandwidth interconnect• Peak rate 6.4 GByte / s• Application transparent

Interactive Parallel Ray Tracing

r

Distance measurementLine end-points are placed with the mouse. Rays are fired through the respective pixels to determine the end-point positions.

Component IdentificationThe mouse simply needs to be positioned over the part to be identified. Extra rays are shot to find the ID of the visible component.

Physically correct shadingSoft shadows significantly enhance the impression of shape and depth.

For real-time display of highly complex models, ray tracing provides a better alternative than rasterization. Ray tracing algorithms closely model physical light transport by shooting rays into the virtual scene. By employing spatial index structures, ray-object intersections can be found efficiently, resulting in a logarithmic time complexity with respect to scene size. Additionally, because of the algorithm’s output sensitivity, only data that is actually visible is eventually accessed. This allows to directly visualize complex datasets pixel-accurately without any kind of simplification or approximation.

Since the colors of different pixels can be calculated independently of each other, ray tracing offers an extremely high degree of parallelism. By assigning different pixels to different processing units, it is therefore possible to reach even real-time performance of up to 15 frames / s (no shadows).