# Where should the ray origin be put in perspective camera ray tracing?

Where should the ray origin be put in perspective camera ray tracing?

The following gives a picture of the ray tracing in the perspective camera setting: http://www.cs.cornell.edu/courses/cs4620/2011fa/lectures/06raytracingWeb.pdf

and says that the $e$ is the ray origin, which is the same for all rays. However, I don't understand how is $e$ supposed to be selected. Can it be the zero vector? Or perhaps it's supposed to be the camera center?

• You add a link but you don't say how it relates to your question. Please edit your question to explain fully what you understand and what you don't. – Dan Hulme Aug 6 at 19:20

Depends on the system you are using. Maybe your camera is fixed at the origin and only the world rotates/moves. In this case, usually the camera is fixed at the origin looking in either the +Z or -Z direction depending on if it's left or right handed coordinates system. So the ray origins will be fixed at (0,0,0).
• I'm given camera center point, so should I use it as $e$? – mavavilj Aug 6 at 20:03
• It's the center where the camera originates. The it also gives me $up$ vector, which points upwards from the camera, also an angle and a direction (where the camera points). – mavavilj Aug 6 at 20:14