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  <section id="glossary">
<h1><span class="section-number">11. </span>Glossary<a class="headerlink" href="#glossary" title="Link to this heading">¶</a></h1>
<p>A glossary of the key concepts used in Raysect.</p>
<dl class="simple">
<dt>Affine Matrix</dt><dd><p>A 4x4 matrix which defines a transformation between two coordinate
systems. See <a class="reference internal" href="api_reference/core/affinematrix.html#raysect.core.math.affinematrix.AffineMatrix3D" title="raysect.core.math.affinematrix.AffineMatrix3D"><code class="xref py py-class docutils literal notranslate"><span class="pre">AffineMatrix3D</span></code></a>.</p>
</dd>
<dt>Flux</dt><dd><p>See radiant flux.</p>
</dd>
<dt>Intensity</dt><dd><p>The radiant flux per solid angle. Note that this is not the same
as radiance, and in practice not very useful except for comparing
point sources.</p>
</dd>
<dt>Intersection</dt><dd><p>A ray-primitive intersection that describes the point of intersection
between the given ray object and a piece of geometry (a primitive) in
the scene <a class="reference internal" href="api_reference/core/core_classes.html#raysect.core.intersection.Intersection" title="raysect.core.intersection.Intersection"><code class="xref py py-class docutils literal notranslate"><span class="pre">Intersection</span></code></a>.</p>
</dd>
<dt>Irradiance</dt><dd><p>The area density of radiant flux passing through a surface, symbol
<span class="math notranslate nohighlight">\(E\)</span>, with units W/m^2.</p>
</dd>
<dt>Material</dt><dd><p>A material object provides an associated primitive with physical
surface and volume properties. e.g. <code class="xref py py-class docutils literal notranslate"><span class="pre">core.material.Material</span></code>
and <code class="xref py py-class docutils literal notranslate"><span class="pre">optical.material.Material</span></code></p>
</dd>
<dt>Node</dt><dd><p>A fundamental element of the scene-graph with its own local coordinate
system <a class="reference internal" href="api_reference/core/raysect_core_scenegraph.html#raysect.core.scenegraph.node.Node" title="raysect.core.scenegraph.node.Node"><code class="xref py py-class docutils literal notranslate"><span class="pre">Node</span></code></a>.</p>
</dd>
<dt>Observer</dt><dd><p>An observing node of the the scene-graph that generates rays to sample
the scene. Observers can be 0D (Pixel, FibreOptic) or 2D
(PinholeCamera). Observers are responsible for all the geometric
effects of the observing process, such as the pixel area and
solid angle sensitivity that define an effective etendue for the
observer. After ray-tracing the results of all the samples are
passed to a list of connected pipeline objects for further data
procressing. See <a class="reference internal" href="api_reference/optical/observers.html#observers-page"><span class="std std-ref">Observers</span></a> for more examples.</p>
</dd>
<dt>Pipeline</dt><dd><p>Pipelines are responsible for the data analysis of observers after
ray-tracing. They process the mean spectral radiance at each sample
location (could be 0D or 2D) into the more specific data type the
user is interested it. For example, users may be interested in
converting mean spectral radiance values to the more human friendly
RGB colour or raw power values. See <a class="reference internal" href="api_reference/optical/observers.html#observers-page"><span class="std std-ref">Observers</span></a> for more
examples.</p>
</dd>
<dt>Primitive</dt><dd><p>A geometric structure that interacts with rays and is also a scene-graph
node. May define a closed or open surface, and a volume. Examples of
primitives are geometric shapes, such as the Box and Cylinder, as well
as structured meshes. All primitives have a material applied to their
surface and volume. See the <a class="reference internal" href="api_reference/primitives/primitives.html#primitives-module"><span class="std std-ref">Primitives Module</span></a>.</p>
</dd>
<dt>Radiance</dt><dd><p>Radiance is the flux density per unit area per steradian, W/m^2/str, given
the symbol <span class="math notranslate nohighlight">\(L\)</span>. Radiance is the most fundamental radiometric quantity
since all other quantities can be calculated as integrals of radiance over
areas and solid angles. Radiance is the natural quantity for ray-tracing
because it remains constant along rays in empty space.</p>
</dd>
<dt>Radiant Flux</dt><dd><p>Also known as power, the total amount of energy passing through a surface
in one second, i.e. units of watts (W) with the symbol (<span class="math notranslate nohighlight">\(\Phi\)</span>).</p>
</dd>
<dt>Ray</dt><dd><p>Describes a line in space with an origin and direction. Ray’s are used to
trace() the world (e.g. <a class="reference internal" href="api_reference/core/core_classes.html#raysect.core.ray.Ray" title="raysect.core.ray.Ray"><code class="xref py py-class docutils literal notranslate"><span class="pre">core.ray.Ray</span></code></a> and <a class="reference internal" href="api_reference/optical/main_optical_classes.html#raysect.optical.ray.Ray" title="raysect.optical.ray.Ray"><code class="xref py py-class docutils literal notranslate"><span class="pre">optical.ray.Ray</span></code></a>).</p>
</dd>
<dt>Scene</dt><dd><p>A particular scene-graph instance consisting of geometry and cameras that
correspond to a physical scene.</p>
</dd>
<dt>Scenegraph</dt><dd><p>A tree structure that represents a nested set of coordinate systems. Changes
to the coordinate system at any node level are cascaded to all children. For
example, suppose you have a car node that contains separate child nodes for
each of the wheels and car body. Any transform applied to the car node,
would also be applied to each of the cars component parts. The scenegraph
makes it easy to manage complex scenes by allowing complex nodes to have
their own local coordinate system. Any instanced node objects (e.g. boxes,
lenses, etc) that are not connected to the scene-graph will not be included
in the ray-tracing. It is possible to have multiple worlds (scene-graphs) in
the same script for cases where you need to trace two different scenes and
compare the results.</p>
</dd>
<dt>Solid Angle</dt><dd><p>The two dimensional angle in three dimensional space that an object subtends
at a point. It represents how large an object appears to an observer at that
point. Measured in units of steradian (str). There are <span class="math notranslate nohighlight">\(4\pi\)</span> steradians
in a sphere.</p>
</dd>
<dt>Transform</dt><dd><p>A 4x4 affine matrix which defines a transformation between two coordinate
systems. See <a class="reference internal" href="api_reference/core/affinematrix.html#raysect.core.math.affinematrix.AffineMatrix3D" title="raysect.core.math.affinematrix.AffineMatrix3D"><code class="xref py py-class docutils literal notranslate"><span class="pre">AffineMatrix3D</span></code></a>.</p>
</dd>
<dt>World</dt><dd><p>The root node of the scene-graph on which ray-tracing is performed, it also
holds the acceleration structures used by the ray-tracer. See
<a class="reference internal" href="api_reference/core/raysect_core_scenegraph.html#raysect.core.scenegraph.world.World" title="raysect.core.scenegraph.world.World"><code class="xref py py-class docutils literal notranslate"><span class="pre">core.scenegraph.world.World</span></code></a> and <a class="reference internal" href="api_reference/optical/main_optical_classes.html#raysect.optical.scenegraph.world.World" title="raysect.optical.scenegraph.world.World"><code class="xref py py-class docutils literal notranslate"><span class="pre">optical.scenegraph.world.World</span></code></a>.</p>
</dd>
</dl>
</section>


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