Every render engine has its own set of lights and materials therefore it is important to pick lights for rendering with Arnold always from the Arnold menu. Add > Arnold > Lights > Skydome Light.
At the Color attribute of the aiSkyDomeLightShape click on the Texture checkerboard icon and in the Create Render Node popup choose the > Arnold > Texture > Environment > aiPhysicalSky. Alternatively you can select the > Maya > 2D Texture > File node and load an external HDR (High Dynamic Range) image. With their higher bit depth (32bit) HDR images are able to capture the lighting information from real world environments which is helpful to illuminate photorealistic scenes. You can downlad free HDR samples from the sibl archive. When you load 32bit HDR images in Maya (.hdr or .exr) make sure to change the Color Space to Raw. Jpeg and everything else should remain at sRGB. Find out more about the new Maya 2017 color management in the Arnold User Guide.
I’m interested in a more artificial look and will continue with the aiPhysicalSky.
Once we have a light in the scene it would render without background:
To add a background go to the Render Settings with the little icon from the shelf. Switch to > Render Using Arnold Renderer. At the tab > Arnold Renderer > Environment click on the Background checkerboard icon and select the aiPhysicalSky.
The aiPhysicalSky node is only available here if you have it created in the previous step with the Skydome Light. If you have decided to use a HDR image for lighting you can use the same HDR file as background image. Since the background image linked at the Render Settings does not contribute to lighting, you can use any file here (also regular 8 bit jpeg images). The free HDR samples from the sibl archive come mostly with high resolution jpeg images, they should be preferred here.
At the Color attribute of the aiSky node click on the Texture checkerboard icon, in the Create Render Node popup choose the > Maya > 2D Textures > File node and load an external image.
To make the support geometry of the aiSkyDomeLight or aiSky invisible in the viewport you can switch off the LOD Visibility at the Attribute Editor.
Now with the groundplane selected RMB > Assign New Material.
In the popup window select > Arnold > Shader > Surface > aiStandard.
In the Attribute Editor change the diffuse color. Click on the IPR (Interactive Render Preview) button. You might notice a black gap between the terrain and the horizon.
The Physical Sky model renders everything black below a latidude of 0 degrees. To fix it create another Poly Plane with no subdivision, scale it to a value of 10000000 (=100 km) place it slightly below the terrain to avoid intersections and with RMB > Assign Existing Material (the same terrain material). If you have changed geometry in your scene you need to klick on the IPR refresh icon to update it. Other changes in the scene like navigation or shader modifications are automatically updated.
In the aiPhysicalSky node you can influence the lighting and color mood by changing Elevation and Azimuth of the sun. More information about the Physical Sky model with example pictures can be found in the Arnold Manual.
Continue with Maya & Arnold Part 3 –Three-Point Lighting