ambient intensity

The surrounding background light level excluding all
defined light sources.

bezier surface

A form of parametric surface introduced by Bezier while
working for Renault.

block

See cube.

cad

Computer Aided Drafting. Usually describes a system that
is supposed to replace the engineer's or architec's drafting
board.

cone (primitive)

A cone having its base at the origin, a height of 1 unit up
the z-axis, and maximum radii of 1 unit. Different scaling
of the x and y radii will produce an elliptical cone.

cube (primitive)

A cube centred at the origin, having half lengths of 1
unit. Different scaling of the x, y and z half lengths will
produce a block.

cylinder (primitive)

A cylinder centred at the origin, with a half length of 1
unit up and down the z-axis, and radii of 1 unit. Different
scaling of the x and y radii will produce an elliptical
cylinder.

diffuse intensity

The intensity of light spread diffusely by each object from
each light source. It is proportional to the cosine of the
angle between the viewer, the object and the light source.

from point

See vrp.

gouraud shading

A technique for the smooth shading of objects modeled with
flat patches. The colours for each corner of a patch are
calculated. The colours for the internal points are
calculated by interpolating between the corners.

image plane

The 2-dimensional plane seen by the viewer.

initial ray

A ray emanating from the VRP (View Reference Point) into
the image plane.

instance space

The 3-dimensional coordinate system used in the ray tracer
to hold the primitive objects. It is particularly important
in the calculation of intersection points and surface
normals.

intensity (total)

The intensity of a pixel calculated by the ray tracer from
each of the reflected and transmitted rays, as well as the
diffuse and ambient intensity.

intersection point

The point, closest to (but not behind) the start of a ray,
where the ray (vector) intersects an object. It is
calculated by the ray tracer.

intersection tree

A tree of intersection points, holding points intersected
by the initial plus all reflected and transmitted rays for a
single pixel in the image plane.

light source

An object defined within the scene, which emits light. It
may be any of the basic object types for the purposes of
intersection, but will be treated as a point source at the
centre of the object for the purposes of shading.

matrix

See transformation matrices.

node

A node (intersection point) on the intersection tree.

normal

See surface normal.

origin

The point in world or instance space which has an (x,y,z)
tuple of (0,0,0).

parametric surface

A variety of free form curved surface defined with a
topologically rectangular grid of control points. The
different forms of parametric surface will interpret the
control points differently. They may or may not lie on the
surface itself.

patch

triangular polygon in 3-D space.

pattern

The pattern on the surface of an object. i.e. horizontal or
vertical stripes, or squares.

phong shading

Similar to Gouraud shading. Interpolates the normals, not
the colours.

pixel

A point on the image plane.

point

The (x,y,z) coordinates defining a point in 3-dimensional
space.

primitive instance

A primitive object that has been modified via translation,
rotation and/or scaling to instance it somewhere in world
space. The object still retains all the basic properties of
its primitive.

primitive object

The basic definition of an object with half lengths or
radii of 1 unit, and centre at the origin. See cone, cube,
cylinder, plane, and sphere. It can be rotated, translated,
and scaled to produce a primitive instance in world space.

radius

The radius (in the direction of an axis) of a sphere, the
base of a cone or the base of a cylinder. The radius of a
primitive object is always 1 unit. Note : a sphere has 3
radii, and a cone or cylinder has 2 radii and a half
length. For all practical purposes, a radius and a half
length are synonymous.

ray

See vector.

reflected ray

The ray reflected off an object according to the laws of
physics.

resolution

The number of pixels to be sampled across and down the
image plane. low resolution is about 50x50, high resolution
is around 400x400.

rgb tuple

A structure holding three floating point values
representing the intensity of each of the three primary
colours red, green and blue.

rotation

The rotation of an object about its centre. It is defined
by specifying vectors in the direction of the new y and z-
axes of the object in terms of the old axes.

scaling

The scaling factors of the radii of a primitive object.

scene

A collection of objects in world space as defined by the
user.

sphere (primitive)

A sphere, centred at the origin with radii of 1. Different
scaling of the x, y and z radii will produce an ellipsoid.

surface normal

The vector which is perpendicular to the tangent plane to
the object surface at the intersection point.

texture

Macroscopic (bumps and hollows) or microscopic (roughness)
texture mapped onto the surface of an object.

to point

The (x,y,z) tuple that is rendered at the centre of the
image.

translation

The movement of an object's centre from the origin to a
point in world space. It is defined by specifying the
(x,y,z) coordinates of the object centre.

vector

A structure containing two (x,y,z) tuples. The first of
these (v.p) holds the (x,y,z) coordinates of the start point
of the vector (ray); and the second (v.r) holds the (x,y,z)
coordinates indicating the direction of the vector (i.e. the
relative changes in the direction of each of the three
axes). For instance, a vector having v.p=(0,0,0) and
v.r=(1,1,1) would start at the origin and extend into the
positive octant in a direction at 45 degrees to each axis.

viewing angles

The horizontal and vertical angles (in degrees) between the
VPN (View Point normal) and the outer limits of the image
plane.

viewing area

The portion of the scene seen through the image plane.

vpn

View Point Normal. This is the direction of the view into
the scene. VRP and vpn together give a vector, originating
at vrp and extending towards the To point.

vrp

View Reference Point. This is the (x,y,z) coordinates in
world space indicating the point from where the viewer
(user) views the scene.

vup

View Up Vector. This is the direction considered by the
viewer to be up.

world space

A 3-dimensional area in which objects may be defined to
produce a scene.

(x,y,z) tuple

A group of three numbers representing a 3-dimensional point
or vector.