note

VDB

http://www.museth.org/Ken/Publications_files/Museth_TOG13.pdf

We have developed a novel hierarchical data structure for the efficient representation

of sparse, time-varying volumetric data discretized on a 3D

grid. Our “VDB”, so named because it is a Volumetric, Dynamic grid that

shares several characteristics with B+trees, exploits spatial coherency of

time-varying data to separately and compactly encode data values and grid

topology. VDB models a virtually infinite 3D index space that allows for

cache-coherent and fast data access into sparse volumes of high resolution.

http://www.openvdb.org/documentation/doxygen/faq.html#sWhatIsVDB

OpenVDB is a library comprising a compact hierarchical data structure and a suite of tools for the efficient manipulation of sparse, possibly time-varying, volumetric data discretized on a three-dimensional grid. It is based on VDB, which was developed by Ken Museth at DreamWorks Animation, and it offers an effectively infinite 3D index space, compact storage (both in memory and on disk), fast data access (both random and sequential), and a collection of algorithms specifically optimized for the data structure for common tasks such as filtering, constructive solid geometry (CSG), discretization of partial differential equations, voxelization of polygons, skinning of particles, volumetric compositing and sampling. The technical details of VDB are described in the paper "VDB: High-Resolution Sparse Volumes with Dynamic Topology".

Mantra

rendering engine > Micropolygon rendering

http://www.sidefx.com/docs/houdini/render/understanding

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Micropolygon rendering was a performance compromise that has largely been supplanted by raytracing in modern rendering setups. The micropolygon algorithm was designed for memory efficiency: geometry is diced and shaded once, then discarded when it is no longer needed (though it remains in memory if it is hit by a ray). Now that we have models with very high polygons counts and machines with tons of memory, raytracing/PBR is usually a more efficient method.

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The "Physically based micropolygon" setting exists in case someone found a need for it, but is not really useful.

The following might be reasons to use the micropolygon rendering engine:

Scenes involving a lot of fur and/or smoke (using deep shadow maps), or sprites, can render more efficiently with micropolygon rendering, provided you are not using ray traced shadows or other ray tracing in the shader. Note that you might want to render fur and volumes as a separate render pass using micropolygon rendering and render the rest of the scene using PBR.

Scenes that require matching existing footage rendered with micropolygon settings.