The ideal point from which all scene rays originate.
Projection Axis
Aka "line of sight", "viewing direction"
The axis from the projection point along the direction of camera view.
Projection Plane
Just putting this here, but we probably shouldn't use this. However, it would be very handy as
an abstract concept when discussing the defocus disk, and "in front of the camera".
The plane containing the projection point and parallel to the focal plane.
The plane on which pixel targets are arranged in world space.
Typically perpendicular to the projection axis.
Image Width, Height
The integer-valued width and height of the rendered image.
Aspect Ratio
The ratio of rendered image width / height.
Viewport
The virtual window in world space through which the camera views the world.
For square pixels, the viewport aspect ratio matches the image aspect ratio.
May be slightly different from the desired aspect ratio, as it will be integer based to match
that of the rendered image.
Focal Distance
Aka "focal length".
The distance from the projection point to the center of the viewport.
Pixel Spacing
The horizontal and vertical distances along the focal plane from one pixel to the next.
For our purposes horizontal and vertical spacing are equal.
Image Grid
An orthogonal grid of pixel locations.
For our purposes, the image grid has equal spacing horizontally and vertically.
Pixel
A sample of the light around a particular point on the rendered image.
One sample integrates the light along a set of rays fired into the scene.
Multiple samples integrate the sampled light of many single samples around the pixel location.
"In front of the camera"
The halfspace parallel to the focal plane, tangent to the projection point, and containing the
focal plane.
Alternatively, any point in world space where the dot product of the projection axis and the
vector from the projection is positive.
Focus Distance
The distance at which geometry appears in perfect focus.
The distance from the projection point to the focal plane.
Defocus Angle
Was specified as defocus diameter.
Specified relative to the viewport center, around the projection point.
Gives the angle of the cone of rays through an image sample to approximate depth of field.
2tan(defocus angle / 2) yields f-stop.
Defocus Disk
Aka "blur disk", "aperture"
The disk from which ray origin points are randomly chosen.
Centered on the projection point.
Orthogonal to the projection axis.
The intersection of the plane containing the projection point and parallel to the focal plane,
and the cone from the viewport center with a given defocus angle.
Scene Rays
A ray from the projection point to the target pixel.
The target may be jittered around the pixel to sample the area around that image location.
The ray origin may be randomly chosing from a defocus disk (below).