RenderMan for Houdini exposes a powerful system of AOV creation called Light Path Expressions.
To specify an AOV you should provide the following information to RenderMan:
In the RenderMan RIS ROP, go to Properties | Ri AOV tab, "Number of AOVs" is a dynamic array of AOVs. Click on the + icon to create an AOV.
Instead of specifying a variable, you can click on the down arrow icon to the right of Variable to get a list of built-in LPEs. When you select an item from the list, it will automatically populate the Variable field, e.g. varying color Ci.
This built-in source string is a convenient list to work with user LPEs that is needed for outputting AOVs forPer-Lobe LPEs.
Some Bxdfs such as PxrSurface require user LPE setup.
To view your AOVs interactively in 'it':
It 'it', expand the down arrow key to see a list of your AOVs. Simply click on the AOV (e.g. Nn.exr in this example) to view it.
To view your AOVs interactively in Render View, set your Display Device to houdini:
Turn on View Bar in your Render View.
You will see a list of your AOVs like the below example:
To output your AOVs to disk, specify the file path and set your Display Device to the file format you want to output to, e.g. openexr.
To output your AOVs into a single EXR (multichannel EXR), you can reference the display channel names with comas. In the example below, we have two display channels: mydiffuse and myspecular. When you leave Display and Display Device blank, RfH will just emit the DisplayChannel. Then you can use those channels to output one multichannel EXR for the AOVs.