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Scale is crucial for the behavior of any simulation. The real-world size of the Simulator in units is important for the simulation dynamics.

Large scale simulations appear to move slower, while mid-to-small scale simulations have lots of vigorous movements.

As the focus of this tutorial is a large-scale simulation, setting the units to Meters is a reasonable choice.

Go to Windows → Settings/Preferences → Preferences and then click on Settings. Underneath the Working Units, change the Linear dropdown to meter and click Save.

Note that when you create your Simulator, you must check the Grid rollout where the real-world extents of the Simulator are shown.

If the size of the Simulator in the scene cannot be changed, you can cheat the solver into working as if the scale is larger or smaller, by changing the Scene Scale option in the Grid rollout.

We also want to make sure our Color Management preferences are set to work properly. If you're using a version of Maya 2018, 2019 or 2020, you can leave the Color Management settings at the default values, which should be in sRGB rendering space.

If you're using Maya 2022 or later, head to the next step below.

If you're using Maya 2022, the Color Management settings have been changed to ACEScg by default.

We need to switch them to sRGB settings, so that the render results in this tutorial remain consistent with earlier versions of Maya as well.

In the Color Management section, change the Rendering Space to scene-linear Rec.709-sRGB.

Set the Display to sRGB.

Set the View to Raw.

Initial scene setup consists of the following elements:

1. A deformed Torus Knot geometry that is used for the smoke source.
2. Phoenix Fluid Simulator (PhoenixFDSim1).
3. Phoenix Fire/Smoke Source (PhoenixFDSrc1) emitting Smoke from the Torus Knot geometry.
4. VRayLightSphere1 light for lighting.
5. Camera1 for look-development rendering.
6. Phoenix Turbulence (PhoenixFDTurb1) for adding variation to the Smoke's motion.

The final scene setup consists of the following elements:

1. An original Phoenix Fluid Simulator (PhoenixFDSim1) + five instances (PhoenixFDSim2 - PhoenixFDSim6).
2. Three additional VRayLightSpheres (VRayLightSphere2 - 4) for lighting.
3. A Semi-circular Curve, serving as a camera animation path.
   
4. Camera2 for the final animation render. Camera2 is path constrained to the Semi-circular Curve.
5. An nParticle grid used to replicate stars.
   

If you're using Maya 2018 or an earlier version, note that you will need to adjust a setting in order for the Camera2 animation to function as expected.

Simply set the Maya Preferences → Animation → Evaluation mode to DG, and this will produce the proper behavior and results for Camera2's animation path.

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Lights Settings

nParticle Settings

Camera Settings

Go to the menu for PhoenixFD → Create → 3D Simulator.

The exact position of the Phoenix Simulator in the scene is XYZ: [ -2.0, -0.17, 0.0 ].

Open the Grid rollout and set the following values:

Create a Phoenix Fire/Smoke Source in the scene by going to: PhoenixFD → Create → PHXSource.

Select the TorusKnot geometry as the emitter, and then press CTRL+LMB and click on PhoenixFDSrc1, so that both the Torus and PHXSource are selected. Then, press the Add Selected Objects button in the PhoenixFDSrc1 attributes.

For the PhoenixFDSrc1:

Set the Emit Mode to Surface Force, Discharge to 1.0 and Smoke to 4.0.

Disable the Temperature option.

In the Simulator → Simulation rollout, disable Use Timeline Stop Frame, and set the Custom Stop Frame to 30.

Here is a Preview Animation of the simulation up to this step. It looks a bit dull now and does not yet resemble anything like a nebula.

Go to Phoenix FD → Create → Turbulence.

Position to XYZ: [ -2.5, 14.0, 9.0 ].

Set the Strength to 350.0 and the Size (units) to 30.0.

Reduce the Fractal Depth to 1.

Set the Decay type to Inverse square.

Then go to the Phoenix Simulator and run the simulation again.

Here is a Viewport Preview showing the result of the simulation so far.

Go to the Phoenix Simulator → Rendering rollout.

Drop down the Fire rollout, and set the Based on option to Disabled.

For the Smoke Opacity rollout, set the Based on option to Smoke.

Then, adjust the Opacity curve below, as shown in the image.

Alternatively, you can simply load up a Rendering Preset using the Nebula_Rendering_Preset.mel file, that is provided with the sample scene.

Note that there is an additional .mel preset file as well, which contains additional tweaks that we'll create near the end of the tutorial.

Since we are going to render a very heavy volumetric scene, we will use V-Ray GPU as our renderer.

Since Global Illumination does not contribute a lot to this scene, let's disable theGI in the Render Settings → GI tab.

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For preview purposes, let's make sure that only the VRayLightSphere1 is enabled. Set its Intensity multiplier to 10 for now, until we enable the other lights later on.

Open the Phoenix Simulator → Resimulation rollout and enable Grid Resimulation.

Note that when you enable Resimulation, Phoenix will try to read the cache files for preview and rendering from the Resimulation Output Path, instead of the 'regular' Output. Don't worry if the Viewport goes blank and the preview disappears - you can always go back to the original cache files by disabling the Resimulate checkbox.

Set the Amplify Resolution to 0.2. This parameter is used to increase the resolution of the grid during the Resimulation process.

Set the Amplify Method to Wavelet Nice and Wavelet Strength to 1.0.

Press Simulator → Simulation rollout → Start to begin the Resimulation.

Next we will move and rotate the Simulator instances in the scene, and arrange them to match the screenshot on the right.

Rotate the PhoenixFDSim1 simulator -20 degrees on the Y axis.

Now we will have a more noticeable gap in the center of the nebula, for V-RayLightSphere1 to shine through. This will help to create a more pleasing composition, in tandem with the additional duplicated nebulas.

Also rotate theTorus Knot geometry -20 degrees on the Y axis as well. That way if you decide to simulate again later, the Torus Knot will already be rotated.

Here is a test render up to this step. 

So far so good, but the VRayLightSphere1 is too bright relative to the other lights, so let's bring that down a bit.

Lower the Intensity multiplier to 4.0 for the VRayLightSphere1, so that it is more balanced with the rest of the lights we just enabled.

Now both the lighting and volumetric simulation are ready for rendering. We'll then do some Color Corrections in the V-Ray Frame Buffer, to bring out the detail and make the image more dynamic.

Also, to render out the stars, make sure to unhide the nParticles in the scene, and then do a render and proceed to the next step.

Open the V-Ray Frame Buffer and use the Create Layer icon to add layers for Filmic Tonemapping, Color Balance, Curves, White Balance and Lens Effects.

The final image is rendered using the V-Ray Frame Buffer with the color corrections & post-effects set to:

Filmic Tonemap:

• Blending: Overwrite, 1.000;
• Tone mapping space: Linear sRGB;
• Type: Hable;
• Log space: disabled;
• Gamma: 1.000;
• Shoulder strength: 0.670;
• Linear strength: 0.070;
• Linear angle: 0.490;
• Toe strength: 0.270;
• White point: 7.880.

Color Balance:

• Blending: Overwrite, 1.000;
• Selection mode: All;
• Cyan - Red: -0.093;
• Magenta - Green: -0.020;
• Yellow - Blue: -0.082.

Curves:

• Adjust it to an S-shape curve as shown in the screenshot.
• Blending: Overwrite, 1.000;
• 1st Coordinate: [-0.00746, 0.00862];
• 2nd Coordinate: [1.000, 1.004].

White Balance:

• Blending: Overwrite, 1.000;
• Temperature: 6519.126;
• Magenta - Green tint: -0.040;
• Color Tint (RGB): [1.000, 1.000, 1.000].

Lens Effects:

• Opacity: 1.000;
• Enable bloom/glare;
• Size: 11.110;
  
• Intensity: 0.050;
• Bloom: 0.500;
• Threshold: 0.570;
• Rotation: 0.000;
• Saturation: 1.000;
• Enable Hardware accelerated;
• Enable Cold/Warm;
• Enable Interactive;
• For Aperture Shape:
  • Enable Blades;
  • Sides: 4;
  • Blade rotation: 45.000;
  • Streak blur: 0.200;

• Everything below in the Lens Effects is disabled.

Feel free to use other values for the post effects, depending on your preferences.

Alternatively, you can simply load up the Color Corrections Preset from the Nebula_VFB_CC.vfbl file that is provided in the sample scene.

As a final step and to further enhance the realism of the nebula, let's also introduce some Color Absorption, which controls the color of the volumetric shadows and the tint for the objects seen through the volume. Select the Phoenix Simulator, go to Rendering → Smoke Opacity.

Set the Absorption Constant Color to a green RGB (91, 96, 55).

Alternatively, you can load in the final preset file Nebula_Rendering_Preset_02.mel which contains the final Absorption Constant Color as well.

Here is the final rendered image with the Absorption Color and Color Corrections we set up earlier.

Tweaking the Absorption Color setting brings out additional details and colors in the nebula, especially around the brighter areas.