This page provides information on the V-Ray Volume Grid tab.

 

Page Contents

 

Overview


The V-Ray Volume Grid tab contains the main input for the cache file, as well as animation and shading parameters.

 


 

UI Path: ||Select V-Ray Volume Grid|| > Properties viewport > V-Ray Volume Grid Tab

 

 

 

Input Rollout


 

 

 

Input Cache File – Defines the cache file name in one of the three supported volumetric formats. (OpenVDB, Field3D, PhoenixFD). The file name can contain format specifier to describe a sequence of files. V-Ray Volume Grid supports multiple format specifiers:

– <frame0n>, where n is an integer specifying the number of digits, and the optional 0 specifies padding with zeroes. For example, if you enter cache_<frame04>.vdb as the file name, this will be expanded to cache_0000.vdb for frame 0, cache_0001.vdb for frame 1, and so on. The same logic is used for VRayMesh.

– # symbols will be replaced with the current frame number. Multiple symbols can be used to specify the number of digits in the file name. For example cache_###.vdb will be expanded to cache_001.vdb for frame 1.

Show cache info for current frame – Displays information about the size of the volume grids for the current frame,as well as their cache channels and their min and max values.

Flip Up axis – Flips the Up axis (Y or Z) for the loaded cache.

Load Nearest if Missing – If there is no cache for the desired frame number, then the nearest cache frame is found and loaded.

 

Time Bend Controls


 

 

 

Animation Control – Controls how the V-Ray Volume Grid will determine the cache frame to be rendered on the current frame. Note that the frame is not always an integer. In this case interpolation is used to construct a temporary grid in memory.

Linear – The input sequence is controlled by optional cache start offset and play speed. (default)
Frame Index – A direct frame index can be specified and eventually animated.
Loop – A defined piece of the sequence is looped. In this mode the Cache Start parameter specifies where the beginning of the looped sequence is, the Length parameter specifies the length of the loop, and Loop Overlap specifies the number of overlapping frames to ensure a smooth transition. Keep in mind that the end transition frames are not in front of the sequence end, but after it. For example if the loop starts at frame 35, has a Length of 20 and a Loop Overlap of 5, the transition frames will start at frame 55 and will end at frame 59. In such a case, the simulation must be at least 59 frames long. 

Frame Blending – When Play Speed is not 1.0, or a Loop Overlap value is specified in Loop mode, a timeline frame must be constructed from two cache files by blending between them. You can choose between two different methods for blending between cache files.

Interpolation – Simple linear interpolation suitable for slow simulations.
Velocity – Velocity based interpolation, which requires a Velocity channel.

 

Linear Parameters


Cache Start – An offset specifying which cache file from the sequence will be placed on the timeline at the frame specified by Play Start.

Play Start – An offset specifying which timeline frame the starting cache will be placed on.

Play Length – Duration, in timeline frames. In Linear mode when this parameter is larger than 0, the sequence length is limited to this value. In Loop mode this parameter specifies the loop length.

Play Speed – A multiplier for the playback speed. Value of 1 means that each timeline frame corresponds exactly to one cache file index. If the play speed is not exactly 1.0, frames will be blended together by using the method specified by the Frame Blending option.

 

Frame Index Parameters


 

 

 

Frame Index – Specifies the input frame number.

 

Loop Parameters


 

 

 

For more details on parameters not unique to the loop animation control type, see the Linear Parameters section above.

Loop Overlap – In Loop mode, number of timeline frames after the loop's end that will be blended with the loop's beginning to make for a smooth transition. It is recommended that this value be longer than the average "lifetime" of the simulation elements. For example if a waterfall is simulated, the "lifetime" is the time the water is flying freely.

 

Render Mode Parameters  


 

 

Render Mode – The technique used to visualize the grid content:

Volumetric – Used mostly for fire and smoke. As with most volumetric shaders, it is based on the raymarching technique.
Volumetric Geometry – Used mostly to export deep images and render elements such as normals, velocity, etc. It produces the same result as the Volumetric mode by using procedural geometry that contains multiple transparent layers. When using this mode, increase the transparency of each layer by increasing the Max transparency levels parameter in Global Options to more than the default value of 50.
Volumetric Heat Haze – Produces the same result as Volumetric Geometry mode, but adding an effect similar to the visual distortion that occurs over hot surfaces (such as pavement in a hot environment). The traced ray changes its direction according to the gradient specified in the Surface channel.  For more information, see the Heat Haze example below..
Isosurface
– Used mostly for liquids. It produces a V-Ray procedural isosurface geometry using the Surface options.
Mesh – Converts the content into a standard mesh using the Surface options. Mostly used for liquids.

 

Volumetric Heat Haze Parameters


 

 

 

Heat Haze – A value of 1 corresponds approximately to the normal heat haze in air caused by the temperature. If smoke or other channel is selected as source, a larger multiplier may be needed to achieve a visible result. For more information, see the Heat Haze example below.

 

Mesh Parameters


 

 

 

Mesh Type – Specifies the technique used to create the mesh.

Static Mesh – Converts the content into a V-Ray static mesh.
Dynamic Mesh – Converts the content into a V-Ray dynamic mesh.

 

 


 

Example - Heat Haze

 

Heat haze adds refraction at each ray-marching step through the volume. To turn on heat haze, choose  Volumetric Heat Haze  as the  Render Mode , and set the  Heat Haze  value to a number greater than 0.

 

 


Heat Haze: Off

 


Heat Haze: On

 

 

 

 


 

Surface Parameters  


This section controls the conversion of the grid content into geometry when Render Mode is set to Mesh or Isosurface. The technique is based on the isosurface concept which is the 3D version of the isoline, well known from topological maps and weather forecasts.

 

Isosurface


Surface from – Controls which physical channel represents the isosurface. By default it is set to the Smoke channel, but other channels can also be isosurface geometry.

Texture – Uses an external texture map. The texture must be linked in Schematic setup to the Surface Texture channel of the V-Ray Volume Grid node.
Liquid/Temperature – Uses the temperature channel.
Smoke – Uses the smoke channel.
Speed – Uses the magnitude of the velocity channel.
Fuel – Uses the fuel channel.

Invert Volume – By default the values above the surface level are considered internal. This option swaps inside and outside. Note that this should be enabled for OpenVDB level sets.

Isosurface Level – The threshold level that determines which cells are considered full/empty. Only cells with values above this level will actually be rendered. The higher the value, the smaller the volume of the isosurface geometry, and vice versa. With higher values, fewer cells will have enough liquid to be visible. Note that for OpenVDB level sets, this should be set to 0.0 to get an accurate result.

 

Mesh


 

 

 

Mesh Smoothing Level – Reduces the roughness of the mesh. The larger the value, the slower the mesh builds.

 

Incandescence Parameters  


 

 

 

Incandescence Input – Specifies the channel that will be used to drive the emissive color of the volume.

Disabled – Disables the emissive color.
Temperature/Liquid – Uses the temperature channel.
Smoke – Uses the smoke channel.
Speed – Uses the magnitude of the velocity channel.
Texture – Uses an external texture map. The texture must be linked in Schematic setup to the Emissive Texture channel of the V-Ray Volume Grid node.
RGB – Uses the RGB channel.
Fuel – Uses the fuel channel.

Modulate with Texture – When Incandescence Input is not set to Texture, the selected channel will be multiplied by the map linked to the Emissive Texture channel in Schematic setup.

Opacity Mode – Determines the method to be used to calculate the opacity of the incandescence component of the volumetric:

Use Diffuse Opacity – Incandescence will use the same opacity that is set in the Diffuse Opacity rollout. This way there will be no emission in cells where there is no smoke.
Fully Visible
– Uses the Opacity Multiplier value to set opacity regardless of other settings.
Use Own Opacity
 – Uses the Incand. Luminance Gradient to determine the opacity.

Opacity Multiplier – Sets the opacity for the effect. Available only when Opacity Mode is set to Fully Visible

Guess input offset and scale from input – The input offset and scale will be set according to the fluid values set in the cache grid selected as input. Try this option before fine-tuning the gradient. The cache grid values at the currently selected frame in the timeline will be used. It is best to make sure to be at a frame that is representative of the frames that are about to be rendered.

Input Offset – Sets the Incandescence Luminance/Color starting position. All preceding positions will use the value at the start of the ramp.

Input Scale – Sets the Incandescence Luminance/Color scale, i.e. the range of positions that will have their values represented by the ramp. All succeeding positions will use the value at the end of the ramp.

Luminance Scale – Scales the output luminance. The Incandescence Luminance represents values between 0 and 1. Bigger values will produce brighter lighting.

Edit Incand. Color Gradient – Opens the Gradient Editor so the Incand. Color Gradient can be edited.

Incand. Color Gradient – Controls the incandescence color via a gradient.

Edit Incand. Luminance Gradient – Opens the Gradient Editor so the Incand. Luminance Gradient can be edited.

Incand. Luminance Gradient – The luminance of the emitted light is determined by the function represented in the diagram control. Along the X axis is the value of the selected source channel (Temperature, Fuel, etc.). The color of the light is set by the gradient control above. 

 

Diffuse Color Parameters



 

Diffuse Input – Specifies the channel that will be used for diffuse color by the shader. By default, it is a uniform simple color.  

Disabled – Disables the emissive color.
Temperature/Liquid – Uses the temperature channel.
Smoke – Uses the smoke channel.
Speed – Uses the magnitude of the velocity channel.
Texture – Uses an external texture map. The texture must be linked in Schematic setup to the Diffuse Texture channel of the V-Ray Volume Grid node.
Simple Color
– Uses a solid color.
RGB – Uses a three-channel color.
Fuel – Uses the fuel channel.

Modulate with Texture – When enabled, the selected channel will be multiplied by the map linked to the Diffuse Texture channel in Schematic setup.

Guess input offset and scale from input – The input offset and scale will be set according to the fluid values set in the cache grid selected as input. This should be used before fine-tuning the gradient. The cache grid values at the currently selected frame in the timeline will be used, so it is best to make sure to be at a frame that is representative of the frames that are about to rendered.

Input Offset – Sets the Diffuse Color starting position. All preceding positions will use the value at the start of the ramp.

Input Scale – Sets the Diffuse Color scale, i.e. the range of positions that will have their values represented by the ramp. All succeeding positions will use the value at the end of the ramp.

Simple Color – Sets the solid color used in the simple color channel.

Edit Diffuse Color Gradient – Opens the Gradient Editor so the Diffuse Color Gradient can be edited.

Diffuse Color Gradient – The Diffuse Color Gradient can be edited in the Gradient Editor here.

Edit Diffuse Color Gradient – Opens the Gradient Editor so the Diffuse Color Gradient can be edited.

 

Diffuse Opacity Parameters


This rollout controls the opacity of the fluid during rendering. Note that the values are per cell, so the total opacity of the fluid will change if the resolution is changed. The parameters displayed vary according to the selection for Opacity Input.

 

 

 

Opacity Input – Specifies the channel that will be used to drive the opacity of the volume.

Simple Smoke – Uses the smoke channel with a predefined analytical formula.
Temperature – Uses the temperature channel.
Smoke – Uses the smoke channel.
Speed – Uses the magnitude of the velocity channel.
Texture
– Uses an external texture map. The texture must be linked in Schematic setup to the Opacity Texture channel of the V-Ray Volume Grid node.
Fuel – Uses the fuel channel.

Modulate with Texture – Enables the selected channel to be multiplied by the map linked to the Opacity Texture channel in Schematic setup.

Simple Smoke Factor – When Opacity Input is set to Simple smoke, this value is used as an opacity multiplier.

Guess input offset and scale from input – The input offset and scale will be set according to the fluid values set in the cache grid selected as input. This should be used before fine-tuning the gradient. The cache grid values at the currently selected frame in the timeline will be used, so it is best to make sure to be at a frame that is representative of the frames that are about to be rendered.

Input Offset – Sets the Opacity Gradient starting position. All preceding positions will use the value at the start of the ramp.

Input Scale – Sets the Opacity Gradient scale, i.e. the range of positions that will have their values represented by the ramp. All succeeding positions will use the value at the end of the ramp.

Opacity Scale – Scales the output opacity. The Opacity Gradient represents values between 0 and 1. Larger values will produce a denser volume.

Edit Opacity Gradient – Opens the Gradient Editor so the Opacity Gradient can be edited.