user: Describe Glossary from the Blender manual or Python API, including usage steps and snippets.

assistant: s quite different from [Axis Angle](#term-Axis-Angle).

    Quaternion values can be interpreted geometrically as defining a point on a unit
    sphere in 4D space. Moving along any *great circle* of the sphere represents rotating
    around a fixed axis, with one full circle matching two full rotations.

Radiosity
:   A global lighting method
    that calculates patterns of light and shadow for rendering graphics images from three-dimensional models.
    One of the many different tools which can simulate diffuse lighting in Blender.

    See also
    [Radiosity (computer graphics)](https://en.wikipedia.org/wiki/Radiosity_%28computer_graphics%29)
    on Wikipedia.

Random Seed

Seed
:   Blender uses pseudo random number generators, which produce numbers that appear to be random,
    but given the same initial condition, they will always produce the exact same sequence of numbers.

    This is a critical feature to get reproducible and/or stable effects
    (otherwise e.g. your hair simulation would change every time you re-run it,
    without any way to control the outcome).

    The **seed** is a number that represents the initial condition of a random generator,
    if you change its seed, it will produce a new sequence of pseudo-random numbers.

    See also [Random seed](https://en.wikipedia.org/wiki/Random_seed) on Wikipedia.

Ray Tracing
:   Rendering technique that works by tracing the path taken by a ray of light through the scene,
    and calculating reflection, refraction, or absorption of the ray whenever it intersects
    an object in the world. More accurate than [Scanline](#term-Scanline), but much slower.

Real User
:   A Blender object, which is a [Data User](#term-Data-User).
    Opposite of [Fake User](#term-Fake-User), which is only a program construct.

Refraction
:   The change in direction of a wave due to a change in velocity.
    It happens when waves travel from a medium with a given [Index of Refraction](#term-Index-of-Refraction)
    to a medium with another. At the boundary between the media, the wave changes direction;
    its wavelength increases or decreases but frequency remains constant.

Render
:   The process of computationally generating a 2D image from 3D geometry.

Resource
:   External files such as images, sounds, fonts and volumes files that can be packed into a blend-file.

Rest Pose
:   The initial transformations of a bone or whole Armature. Can also be called a default pose.
    Defined in Armature Edit Mode by the head, tail, and roll of each bone.
    Any constraint or driver-induced transformation is NOT part of the rest pose.

RGB
:   A color model based on the traditional primary colors, Red/Green/Blue.
    RGB colors are also directly broadcasted to most computer monitors.

Rig
:   A system of relationships that determine how something moves. The act of building of such a system.

Roll

Roll Angle
:   The orientation of the local X and Z axes of a [Bone](#term-Bone).
    Has no effect on the local Y axis as local Y is determined by the location of
    the [Head](#term-Head) and [Tail](#term-Tail).

Rolling Shutter
:   In real CMOS cameras the sensor is read out with scanlines
    and hence different scanlines are sampled at a different moment in time.
    This, for example, make vertical straight lines being curved when doing a horizontal camera pan.
    See also [Rolling Shutter](https://en.wikipedia.org/wiki/Rolling_shutter) on Wikipedia.

Roughness Map
:   A grayscale texture that defines how rough or smooth the surface of a material is.
    This may also be known as a [Glossy Map](#term-Glossy-Map).

Saturation
:   Also known as colorfulness, saturation is the quantity of hue in the color
    (from desaturated – a shade of gray – to saturated – brighter colors).

Scanline
:   Rendering technique. Much faster than [Ray Tracing](#term-Ray-Tracing),
    but allows fewer effects, such as reflections, refractions, motion blur and focal blur.

Scene Referenced
:   An image whose [Luminance](#term-Luminance) channel is not limited.

    See also [Display Referenced](#term-Display-Referenced).

Shading
:   Process of altering the color of an object/surface in the 3D scene,
    based on its angle to lights and its distance from lights to create a photorealistic effect.

Smoothing
:   Defines how [Faces](#term-Face) are shaded. Faces can be either solid (faces are rendered flat)
    or smooth (faces are smoothed by interpolating the normal on every point of the face).

Specular Light
:   A light which is reflected precisely, like a mirror.
    Also used to refer to highlights on reflective objects.

SSS

Subsurface Scattering
:   Mechanism of light transport in which light penetrates the surface of a translucent object,
    is scattered by interacting with the material, and exits the surface at a different point.
    All non-metallic materials are translucent to some degree. In particular, materials such as marble, skin,
    and milk are extremely difficult to simulate realistically without taking subsurface scattering into account.

Straight Alpha
:   See [Alpha Channel](#term-Alpha-Channel).

Subdiv

Subdivision Surface
:   A method of creating smooth higher poly surfaces which can take a low polygon mesh as input.

    See also
    [Catmull-Clark subdivision surface](https://en.wikipedia.org/wiki/Catmull%E2%80%93Clark_subdivision_surface)
    on Wikipedia.

Subdividing
:   Technique for adding more geometry to a mesh.
    It creates new vertices on subdivided edges, new edges between subdivisions and new faces based on new edges.
    If new edges cross a new vertex is created at their crossing point.

Swing

Swing and Twist
:   Refers to decomposition of an arbitrary rotation into a sequence of two single axis rotations:
    a *swing* rotation that aims a chosen axis in its final direction using the shortest possible rotation path,
    followed by a *twist* rotation around that axis.

    This decomposition is available through [Driver Variables](../animation/drivers/drivers_panel.xhtml#drivers-variables-rotation-modes)
    and inputs of the [Transformation constraint](../animation/constraints/transform/transformation.xhtml).
    The [Damped Track constraint](../animation/constraints/tracking/damped_track.xhtml) produces
    a pure *swing* rotation.

    In the [Quaternion](#term-Quaternion) representation the *swing* rotation always has 0 as the X/Y/Z component
    corresponding to the selected axis, while *twist* always has 0 as the other two components.

Tail
:   A subcomponent of a [Bone](#term-Bone). Has X, Y and Z coordinates measured in the [Local Space](#term-Local-Space)
    of the armature object. Used in conjunction with the [Head](#term-Head)
    to define the local Y axis of a bone in [Pose Mode](#term-Pose-Mode).
    The smaller of the two ends when displayed as an [Octahedron](#term-Octahedron).

Tangent
:   A line that intersects a surface at exactly one point,
    a tangent is perpendicular to a [Normal](#term-Face-Normal).

Tessellation
:   The tiling of a plane using one or more geometric shapes usually resulting in [Micropolygons](#term-Micropolygons).

Texture
:   Specifies visual patterns on surfaces and simulates physical surface structure.

Texture Space
:   The bounding box to use when using *Generated* mapping to add a [Texture](#term-Texture) to an image.

Timecode
:   A coded signal on videotape or film giving information about the frame number and time the frame was recorded.
    Timecodes are used to sync media between different recording devices, including both audio and video.

Title Safe
:   Area of the screen visible on all devices.
    Place text and graphics inside this area to make sure they do not get cut off.

Topology
:   The arrangement of *Vertices*, *Edges*, and *Faces* which define the shape of a mesh.
    See [Vertex](#term-Vertex), [Edge](#term-Edge), and [Face](#term-Face).

Transform

Transformation
:   The combination of location, rotation, and scale.
    Can be expressed in [World Space](#term-World-Space) or [Local Space](#term-Local-Space).

Transformation Matrix
:   A matrix that is used to represent the [Transformation](#term-Transformation) of an item.

Triangle
:   [Face](#term-Face) with exactly three [Vertices](#term-Vertex).

UV Map
:   Defines a relation between the surface of a mesh and a 2D texture.
    In detail, each face of the mesh is mapped to a corresponding face on the texture.
    It is possible and often common practice to map several faces of the mesh to
    the same or overlapping areas of the texture.

Value
:   The brightness of the color (dark to light).

Vertex

Vertices
:   A point in 3D space containing a location.
    Vertices are the terminating points of [Edges](#term-Edge).

Vertex Group
:   Collection of [Vertices](#term-Vertex).
    Vertex groups are useful for limiting operations to specific areas of a mesh.

Voxel
:   A cubic 3D equivalent to the square 2D pixel.
    The name is a combination of the terms “Volumetric” and “[Pixel](#term-Pixel)”.
    Used to store smoke and fire data from physics simulations.

Walk Cycle
:   In animation, a walk cycle is a character that has just the walking function animated.
    Later on in the animation process, the character is placed in an environment
    and the rest of the functions are animated.

Weight Painting
:   Assigning [Vertices](#term-Vertices) to a [Vertex Group](#term-Vertex-Group) with a weight of 0.0 - 1.0.

White Point
:   A reference value for white light when all primaries of a color model are combined evenly.

    A white point is defined by a set of [CIE illuminates](https://en.wikipedia.org/wiki/Standard_illuminant)
    which correspond to a color temperature.
    For example, D65 corresponds to 6500 K light and D70 corresponding to 7000 K.

World Space
:   A 3D coordinate system that originates at a point at the origin of the world.
    Compare to [Local Space](#term-Local-Space).

Z-buffer
:   Raster-based storage of the distance measurement between the camera and the surface points.
    Surface points which are in front of the camera have a positive Z value and
    points behind have negative values. The Z-depth map can be visualized as a grayscale image.