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This type of volumetrics can currently load an OpenVDB file (.vdb). This file format can efficiently store very detailed and large volumetrics based on a 3D grid of voxels instead of individual point particles, which makes it more efficient for storing and rendering detailed volumetrics where otherwise billions and billions of individual particles would have been needed. With the 3.1 update, Maxwell Render can now read and render these files directly. Any Maxwell material can be applied to the volumetric object (except an emitter material), although in most cases a simple lambert is enough to create a very convincing volumetric that reacts very realistically to all lighting in the scene. Once you've set the "Field type" parameter to "Volume file based" you can load an .vdb file in the filename parameter.

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OpenVDB parameters

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A volumetric simulation stored in the OpenVDB format can contain several 3D "grids". At the very least it will contain one "base grid" that defines the base volumetric domain of the simulation. It can also contain additional grids, which is data that was calculated during the simulation. This can be temperature, velocity, acceleration, distance between particles and any other data which the simulation software can calculate. These additional grids are loaded using the "Additional Grids for UV" parameter and they can be used to construct the necessary UVs if you wish to visualize this data using a texture such as a gradient.

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• Base Grid: set the name of the base grid inside the VDB file that defines the volumetric domain. Usually this field is called "density". If no name is supplied here, Maxwell uses the first grid present in the file.
• Base Grid densitymultiplier: controls the density of the base grid. Higher values will make the volumetric appear more dense, letting less light through it.
• Additional grids for UV: here you can specify names of other grids usually found in VDB file that describe velocity or temperature, or any other data that was calculated during a simulation (such as particle distance, acceleration etc.). Use a comma to separate the different grid names. These grids can be used to map textures, usually a colored gradient, to better visualize the stored data. For example if the VDB file contains a "temperature" field, this means that the different temperatures of the simulation grid is stored in the file and you can use it to visualize these different temperatures using a blue to red gradient that uses this field as a driver to create the necessary UV map when rendering. Please see the "Texturing OpenVDB volumetrics" below for more details.
• VEC_MOD 0 to 9 min/max: Lets you redefine the range of the corresponding vector grid, before it is normalized to 0,1 space for UV mapping. VEC_MOD_0 corresponds to the first vector grid found in the file, VEC_MOD_1 to the second one and so on.
• FLOAT 0 to 9 min/max: Lets you redefine the range of the corresponding scalar grid, before it is normalized to 0,1 space for UV mapping. FLOAT_0 corresponds to the first vector grid found in the file, FLOAT_1 to the second one and so on.

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