• Rendering Final Gathering

Final gathering is an optional, additional step used to improve global illumination (GI). It increases the number of rays used to calculate GI to smooth out and eliminate adverse lighting artifacts.
  
Because global illumination is calculated from a photon map, rendering artifacts such as dark corners and low-frequency variations in the lighting may occur.
  
By activating final gathering, you increase the number of rays used to calculate global illumination, which reduces or eliminates these artifacts.
  
There is a catch when deciding to use final gathering. Final gathering can greatly increase rendering time. It is most useful for scenes with overall diffuse lighting.
  
Tip Leave final gathering off to preview the scene, then turn it on for the finished rendering. (Increasing the number of photons used to calculate global illumination can also improve global illumination.)

• Photometric Lights

Photometric lights are physically-correct lights. Physically correct lights attenuate as the square of the distance. Photometric properties can be added to both artificial lights and natural lights. Natural lights are the sun and the sky. The natural lighting is represented interactively by a viewport background type.
  
Photometric lights always attenuate using an inverse-square falloff, and rely on your scene using realistic units.

• Render Destination

Rendered images appear either in a viewport or get displayed in the Render Window.
  
When you render a scene, the image can be displayed in either the viewport or the Render Window. This is the render destination.
  
The render destination is set in the Advanced Render Settings palette in the Render Context section. The default setting is Window.
  
When the render destination is set to Window, the renderer automatically opens the Render Window and the image is processed. Upon completion, the image is displayed and a history entry is created. As more renderings occur, they are added to the render history so you can quickly look at previous images and compare to see which have the desired results. Images that you want to keep can be saved from the Render Window.
  
If you choose to set the render destination to Viewport, the generated image is rendered and displayed directly in the active viewport. In essence, this is a one-time rendering because there is no render history entry that you can compare with later images. If you want to keep the image that you rendered to the viewport, you can use the SAVEIMG command to save the images.
  
Rendering to a viewport always renders against the background color you set for the drawing area. The Render Window background color matches the background color. Use the REGEN command to refresh the display.

• 3D ALIGN

In 3D, use the 3DALIGN command to specify up to three points to define the source plane followed by up to three points to define the destination plane.

• The first source point on an object, called the base point, is always moved to the first destination point.
• Specifying a second point for either the source or the destination results in the selected objects being rotated.
• A third point for either the source or the destination results in further rotation of the selected objects.