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

 

Page Contents

 

Overview


The V-Ray Volume Grid Advanced tab contains control for channels such as Dispacement along with shading options and visibility.

 


 

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

 

 

 

Displacement


Displacement is a technique intended to add detail to the simulation during rendering. The idea of the displacement is similar to geometry displacement, where a texture is sampled and points are shifted in a direction at a distance determined by the texture.

 

 

 

Enable Displacement – Turns on displacement rendering for the volume.

Multiplier – Additional multiplier for the displacement amount.

Type – Chooses between these displacement techniques.

Gradient driven – Requires a monochrome texture map. The point is shifted toward the field's gradient by the texture brightness. This method is suitable for smoke and fire. If not displacing the default temperature channel, select the proper one from the Surface list.
Surface driven – Requires a monochrome texture map. The point is shifted by the texture brightness toward the normal of the point's projection on the isosurface, and the texture is also sampled at the projection point. This method is slower than Gradient driven, but produces better results, similar to displaced geometry. For smoke and fire, be sure to select the proper channel from the Surface list.
Vector – Requires a colored vector texture map (with negative and positive values). The point is shifted by the texture color interpreted as 3D vector. This displacement mode is intended to be used with meshes and produce a similar result to normal V-Ray displacement.
Advection – Requires a colored vector texture map (with negative and positive values). A very similar method to the Vector, but does not produce grainy structures for fire and smoke.

 

 



Example - Advection Displacement

 

 

Regular smoke and fire, 5M cells

 

Advection displacement with the simulation's own velocity,
and a modified noise map
 

 

 

 


 

Map – Specifies the displacement map. Depending on the Type selected, a monochrome map or a color map could be required. The texture used for displacement must be linked in Schematic setup to the Displacement Texture channel of the V-Ray Volume Grid node.

If a colored map is passed when a monochrome map is needed, the strength of the displacement is determined by the total intensity of the color. For more information, see the Surface Driven vs. Vector Displacement example below.

Note: If a monochrome map is used when a vector (color) map is needed, the entire displacement will point in a single direction.

 

 

  


 

Example - Surface Driven vs. Vector Displacement

 

 


Surface driven displacement

 


Vector displacement

 

 

 

 


   

Example - Vector vs. Monochrome Map for Advection Displacement

 

 

Advection displacement with
a vector map between -1 and 1

 

Advection displacement with
a monochrome map between 0 and 1

  

 

 

Shading Options 


 

 

 

Enable Rendering – Turns rendering on or off. When disabled, the cache data is still loaded.

Jittering – When rendering a volumetric object, some artifacts might occur due to the regular raymarching step. Enabling this option prevents artifacts by adding a small random offset to the step. 

Rend. Step (%) – The raymarching step, as a percentage of the cell size. As the renderer traces rays through the simulator, this percentage tells it how often to get information from the grid. If the step is more than 100, some cells will be skipped which can result in artifacts. If you are rendering atmospherics with a specific transparency curve, you may need a lower percentage so that you don't lose fine details. On the other hand, increasing the step increases the rendering speed. This parameter does not affect the rendering when Render Mode is set to Mesh.

Shadow Step (%) – Percentage of the cell size. Lower values will take longer to render.

Fade Out – Content near the grid's boundaries becomes more transparent, in the event that sharp edges are not desired while rendering. This parameter controls how far from the boundaries the process should start.

Velocity Multiplier – Multiplier for motion blur.

Sampler Type – Determines how to calculate the values in the points with non-integer coordinates.

Box – Displays cells as cubes. There is no blending between neighbor cells. The fastest mode.
Linear – Linear blending between neighbor cells to smooth out the fluid's look. Still, sometimes it can expose the grid-like structure of the fluid. Can be 20-30% faster than the Spherical option.
Spherical – Special weight-based sampling for the smoothest looking fluid. With increasing resolution, the visual advantage compared to the Linear method becomes less noticeable.

Coordinate Method – Specifies the method for generating texture coordinates.

Fixed – Uses a fixed texture coordinates method.
Grid
– Uses a grid texture coordinates method.

 

 


 

Example - Rend. Step and Jittering

 

This example illustrates how Jittering and Rend. Step can be used to improve the quality of the raymarching.

 

 


Rend. Step = 50%, Jittering enabled

 


Rend. Step = 150%, Jittering enabled

 


Rend. Step 150%, Jittering disabled

 

 

 

 


 

Diffuse Scattering


 

 

 

Use Light Cache – Enables the use of the light cache for diffuse lighting.

Light Cache Undersampling – Optional reduction of the light cache quality when using area lights. By default, this value is 0.9 and the lights will be sampled with their maximum subdivs (ignoring the Image Sampler settings).

Scattering – Used to disable the scattering of the rays in the volume when GI is used and to select how the light will be calculated. When the scattering is disabled the additional multiplier can be used to adjust the the brightness of the diffuse color.

Ray-Traced (GI only) – If Global Illumination is enabled, this mode enables the scattering of light rays. Otherwise it is the same as the Disabled option.
Disabled
 – In this mode the scattering of light through the smoke is disabled. The Diffuse Multiplier parameter can be used to correct the brightness of the diffuse color in this mode.
Analytic 
– Without actually altering the rays, an analytic formula is used to calculate the contribution of the scattering to the illumination. Brighter smoke transfers light further than dark smoke. Analytic scattering is not supported when Render Mode is set to Volumetric Geometry.
Analytic+Shadows – Same as the Analytic option, but geometry is also affected via the shadows. Analytic+Shadows scattering is not supported when Render Mode is set to Volumetric Geometry

Diffuse Multiplier – The multiplier for the diffuse color. It is ignored when rendering with GI and Scattering is set to any mode but Disabled.

Own Lights Multiplier – A multiplier that affects how far the light from the volume's own emissive lights travels through the volumetric. This option is valid only when Scattering is set to Analytic or Analytic+Shadows.

External Lights Multiplier –The multiplier of how far the light travels through the volumetric from the external emissive lights . This option is valid only when Scattering is set to Analytic or Analytic+Shadows.

Shadows Strength – The multiplier for the shadow opacity that the volumetric casts on other objects.

 

Ray-Traced (GI Only) Parameters


 

 

 

Scatter Depth – Limits the global illumination scattering depth. This can be used to improve performance.

Shadows Strength – A multiplier for the shadow opacity that the volumetric casts on other objects.

 

Light from Incandescence


 

 

Enable Lighting – When enabled, V-Ray Volume Grid will create additional lights in the scene to approximate the incandescent indirect lighting. Enabling lighting can speed up or replace true GI calculations.

Light Power on Scene – Controls the power of the light on all other scene objects, except the V-Ray Volume Grid itself.

Light Power on Self – Controls the power of the light on the V-Ray Volume Grid's smoke. This will not change the strength of the fire, only the illumination it produces on the smoke.

Light Cut-off – Same as the V-Ray Light package Cut-off Threshold parameter. This parameter specifies a threshold for the light intensity below which the light will not be computed. This can be useful for limiting the effect of the lighting to some distance around the V-Ray Volume Grid. Larger values cut away more light; lower values make the light range larger. If this value is 0.0, the light will be calculated for all surfaces in the scene even if they are receiving very little light. This will slow down the rendering, particularly for scenes with many objects.

Reduce Grid to (%) – Reduces the grid to this percentage of its original density. To calculate perfect illumination from fire, each fire cell must be converted to an omni light. This could take a tremendous amount of time to render, though. This is why emissive lights can be created at a lower resolution to speed up rendering at the expense of some illumination detail, which might not always be visible anyway. The more you decrease this value, the smoother the illumination will become and eventually the fire might not blend well with the light it casts on the smoke. A value of 100% produces no reduction. See the Grid-based Self-shadowing with Reduce Grid to % example below.

Self-shadowing – Enables self-shadowing of the smoke from the light of the fire. If this option is enabled, using smoke Scattering will generally help the light to illuminate a larger portion of the smoke, creating a more realistic self-illumination effect.

None – Smoke will not obstruct the light propagation and will be brightly lit.
Ray-traced – The same mechanism that illuminates the scene geometry will be used on the smoke as well. This mode is physically correct and takes into account non–transparent obstacles inside the volume, but requires intense computation and may take considerable time to render.
Grid-based – The self-illumination of the smoke will be calculated separately from the light that the fire casts on the scene using an approximate fast formula. While Ray-traced may produce noise, this mode has no such effect - the resulting illumination on the smoke is always smooth. However, any obstructing obstacles inside the volume are ignored by this mode. The Reduce Grid to (%) parameter can be used to lower the resolution of the light grid and further speed up the illumination process. Reducing the grid will generally make for smoother self-illumination.

For more information, see the Self shadowing example below. 

Decay type – Controls the speed with which the V-Ray Volume Grid's emissive light fades as it propagates through space:

None – The light does not fade at all, unless obstructed.
Inverse – The light intensity fades with the inverse of the distance. For example, at a distance of 5 units, the intensity will be 1/5th of the intensity of the emitter.
Inverse square – The light fades with the inverse square of the traveled distance. This is the physically correct light propagation. For example, at a distance of 5 units, the intensity will be 1/25th of the intensity of the emitter.

Direct Subdivs – Controls the number of rays traced when calculating soft shadows cast by the fire. Higher values increase both shadow quality and render times. Lower values speed up the rendering but produce more noise in soft shadows. If this value is set to 0, a special case is used and all emissive lights are sampled, which can be quite slow when there are a large number of emissive lights.

Caustics Subdivs – Caustic sampling control. Similar to the GI subdivisions, but used when caustics are calculated.  

 

 


 

Example - Self shadowing

 

 


Self-shadowing = None
(render time = 2 min)

 


Self-shadowing = Ray-traced
(render time = 17 min)

 


Self-shadowing = Grid-based, Reduce Grid to (%) = 10
(render time = 1 min)

 

 

 

 


   

Example - Grid-based Self-shadowing with Reduce Grid to %

 

 


Self-shadowing = Grid-based , Reduce Grid to (%) = 1
(render time = 40 secs)

 


Self-shadowing = Grid-based , Reduce Grid to (%) = 10
(render time = 58 secs)

 


Self-shadowing = Grid-based , Reduce Grid to (%) = 100
(no reduction at all), (render time = 6:39 mins)

 

 

 

 


 

 

Visibility


 

 

 

Generate GI – When enabled, the V-Ray Volume Grid will contribute towards the GI.

Generate GI mult. – Multiplier for the amount the V-Ray Volume Grid contributes towards the GI calculation.

Receive GI – When enabled, the V-Ray Volume Grid will receive GI.

Receive GI mult. – Multiplier for the amount the volume grid receives from the GI calculation.

Generate Caustics – Enables the V-Ray Volume Grid to generate caustics.

Receive Caustics – Enables the V-Ray Volume Grid to receive caustics.

Caustics mult. – Multiplier for the amount the V-Ray Volume Grid receives from the GI calculation.

Visible to Camera – Enables the V-Ray Volume Grid to be visible to camera.

Visible to Reflections – Enables the V-Ray Volume Grid to be visible to reflections.

Visible to Refractions – Enables the V-Ray Volume Grid to be visible to refractions.

Visible to GI – When enabled, the V-Ray Volume Grid will be included in the GI calculation.

Cast Shadows – When enabled, the V-Ray Volume Grid will be able to cast shadows upon the scene.