Here is an updated guide on rendering an ambient occlusion render in Maya 2018 with Render Layers and Arnold. Using the Render Setup manager in Maya 2018, you can create separate render layers for your beauty lighting, ambient occlusion, and wireframe renders and switch between them easily and non-destructively.
In Maya 2018, load up your scene and open up an outliner in your interface.
In Windows > Settings/Preferences > Plug-in Manager, make sure the mtoa.bundle is loaded.
Open the Render Setup window to create new render layers. Click on the icon to Create a New Render Layer . Name the layer ambientOcclusion.
Right click on the render layer and click Create Collection. This will allow you to specify which objects belong to the render layer. With the collection tab open, select all geometry in your scene via the outliner, and then press Add. You can switch the Collection Filters to All to make sure the ambient occlusion material will apply to all objects in your scene.
Right click on the new collection and choose Create Material Override. In the Override Material field, click the checkerboard icon to create a new material. In the popup window start typing ambientOcclusion in the filter box and select the aiAmbientOcclusion node.
Click on the the eye icon next to the ambientOcclusion render layer to make it active. And do a test interactive render.
Click on the the icon next to aiAmbientOcclusion1SG to bring up the Attributes for the material.
- Increasing the samples will make the render take longer, but can remove noise (depending on your overall global sampling settings).
- Changing the value of Spread will effectively act like a contrast. The lower the value the smaller the angle of influence will be which will make a sharper transition from light to dark. Leaving this value at 1 is the most common.
- Adjusting the value of the Near and Far Clip depends on your scene size, but can help in scenes where your geometry is entirely enclosed (like in an interior archviz render).
Go back to the Render Setup window to create a new render layer for the wireframe setup. Click on the icon to Create a New Render Layer . Name it wireframe.
Right click on your new render layer and click Create Collection. Add the same objects to your collection that you did in step 4.
Right click on the new collection, and choose Create Material Override. In the Override Material field, click the checkerboard icon to create a new material. In the popup window start typing wireframe in the filter box and select the aiWireframe node.
Click on the the Eye icon next to the wireframe render layer to make it active. And do a test interactive render.
Click on the the icon next to aiWireframeSG to bring up the Attributes for the material. You can change the Edge Type to Polygons. And adjust the line width and colors to your liking.
Back in the Render Setup window, you can click the Eye icon in the top of window to switch back to your masterLayer render and material settings.
If using a cloud rendering service like Zync from Google Cloud Platform, your render layers will appear in the Zync submission window and you'll be able to render them as separate outputs in your batch submission.