I would like to start by saying that the OctaneRender for Carrara plugin does NOT support the native Carrara fire primitive. The built in fire primitive is not a true volumetric and it does not expose any volumetric information that the plugin can use to render it in Octane. Instead, you can load an externally generated OpenVDB file into Octane using the Carrara fire primitive as a proxy. You can then assign a volumetric medium to that primitive to produce a fire like effect. This tutorial will be a step by step guide on how to add and configure an OpenVDB file to a Carrara scene.
First you need to obtain an OpenVDB file that you want to add to the scene. OpenVDB files can be created in some 3D modelling tools including Blender, Houdini, and Realflow. You can also download OpenVDB files from some websites including http://www.openvdb.org/download/
. The file I will be working with is fire.vdb that I obtained from here: http://www.openvdb.org/download/models/fire.vdb.zip
1) Open Carrara and load the smileyjump scene located in the Browser under Scenes->Animations->Smiley Jumps.
2) Add a fire primitive to the scene. Place it to the left of Smiley (your right) and scale it up to a nice size.
3) With the fire primitive selected go to the effects tab. (Remember, there is nothing you can configure on the General tab that will effect the result rendered in Octane.)
4) Under Octane Volume (OpenVDB) set the Enabled flag and click on the [File] button.
5) Locate and open the Fire.VDB file you downloaded from http://www.openvdb.org
6) Click on Import Settings.
7) You should see Absorption Grid and Scattering Grid set to density and Emission Grid set to temperature. There is nothing else to set here so close the window.
8) Switch to the Shading tab (NOT the texture room). Click on the little drop down button and select New Master Shader. Then click Edit.
9) Change the Top Shader to Octane Medium and then change the Medium channel to Volume.
10) Select a dark grey for Absorption and Scattering.
11) In the Emission channel select Texture.
12) Set Power to .02 and set Texture to a RGB Color: Orange
Switch back to the assembly room and then open the Octane Viewport (Edit->Octane Commands->Open Octane Render Window).
A new scale mode was added to the Octane Volume (OpenVDB) Effect.
Fit to Proxy - This mode fits the loaded VDB file into the area reserved by the proxy. Note that this mode will distort the scale of the original VDB object and may not work well with animations.
Fixed Scale - This mode preserves the original scale of the VDB file. The proxy still provides position, rotation, and scale but it does not force the volume to be rendered within the borders of the proxy. A slider and two edit boxes on the new Scale Settings dialog allow you to scale the VDB volume to fit within your scene. Since each VDB file can provide its own initial size, a loaded VDB volume can appear way too large or too small for immediate use. The min-scale/max-scale edit boxes allow you to provide a 'reasonable' range for the Scale slider. Once a min and max scale has been entered, the scale slider can be used to pick a value between the min and max values. This should allow you to more easily tweak the size of the volume to better fit your scene.
Here is my scene. NOTE it does not include the required .vdb file.