6.8. Terminology.   

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.

See cube.

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.

See transformation matrices.

A node (intersection point) on the intersection tree.

See surface normal.

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.

triangular polygon in 3-D space.

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.

A point on the image plane.

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.

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.

See vector.

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

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.

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.

The scaling factors of the radii of a primitive object.

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.

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.

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.

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.

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.

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

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.