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Standard Performance Evaluation Corporation

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Energy viewset (energy-02)

The energy-02 viewset is based on rendering techniques used by the open-source OpendTect seismic visualization application. Similar to medical imaging such as MRI or CT, geophysical surveys generate image slices through the subsurface that are built into a 3D grid. Volume rendering provides a 2D projection of this 3D volumetric grid for further analysis and interpretation.

At every frame, the bounding cube faces of the volume are tessellated and rendered with a fragment shader that performance a ray-cast from the eye position through the volume, accumulating transparent lit, color-mapped values until either the pixel becomes fully opaque or the volume is exited.

The voxel in the 3D grid is a single scalar value. A transfer function -- simply a 1D lookup table -- maps the 3D density value to color and alpha values. For lighting calculations, the gradients are computed on the fly using the central differences at each voxel. These state changes exercise various parts of the graphics subsystem. This viewset makes use of hardware support for 3D textures and therefore trilinear interpolation.

In addition to the volume rendering, the test includes both inline and crossline planes (slices in the X and Y planes). Also, for some subtests, “horizons” are present – these are geological strata boundaries of interest, generated by exploration geophysicists, and are rendered using textured triangle strips.

The 3D datasets used in this viewset are real-world seismic datasets found at https://wiki.seg.org/wiki/Open_data . They were translated from their native SEG-Y format and compressed using JPEG-2000.

Viewset tests

  1. Blake Ridge volume (1307x95x1300) and horizons
  2. F3 Netherlands volume (950x450x462) and horizons
  3. Opunake volume (1949x731x1130)
  4. Blake ridge volume (with animated clipping plane) and horizons
  5. F3 Netherlands volume (with animated clipping plane) and horizons
  6. Opunake volume (with animated clipping plane)