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<div class="moz-cite-prefix">Roy,<br>
<br>
I understand your questions and the underlying issue. I think the
fundamental problem is overloading of the word "lights". When
someone who is working in 3D says lights, it means lighting
sources that illuminate some portion (maybe the entire) scene.
That "light" contributes to the lighting equation that must be
calculated for the scene.<br>
<br>
Physical lights that server to identify boundaries, borders,
extensions (such as running lights, beacons, marker lights, etc.)
are created as different geometry with an emissive color
appropriate to their use. In portions of the scene that is always
lit by scene 3d-lighting, the texture applied to the entire
geometry may have physical-light effects burnt-into the texture.
For example, if I were modeling a truck with running lights, I
would use geometry with an emmisive colour because it is likely
that the truck may be used in a very dark environment. If I were
modeling a building with external splash lighting, I would
probably burn that into the texture of the building side.<br>
<br>
I think we need to be very careful about the meaning of the term
"light". Since we are working in the 3D space, I suggest that it
only mean lighting sources within the 3D environment that
contributes to the lighting equations anywhere in the scene.<br>
<br>
Leonard Daly<br>
<br>
<br>
<br>
</div>
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<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">Leonard,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">Thank
you for this posting. A very interesting discussion.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">First,
let me say I am not contesting your view. I just want to be
sure I understand the common practice.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">I fully
appreciate that development of 3D scenes “in-house” might
easily mean that a modeller only generates the geometry, and
textures, and any lighting, are added at later stages.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">Now,
choosing a ship as an example model that might contain
lights, where the purpose is not so much that they
illuminate the model or any potential surroundings, but are
simply there as identifies to be seen by others. And here I
am thinking of the red and greed marker lights. If a ship
model is developed for sale to, shall we say, the public,
will the model creator simply put these coloured markers on
as coloured materials, perhaps using emissive properties?
And not as a “light source” in the sense of something that
illuminates other content?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">So, if
this is the case, when we say “you don’t have lights”, what
we mean is that “you don’t have light sources, that
participate in the lighting equations”.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">Taking
this one step further, a model creator, even for selling
models, would “never” add “light sources that participate in
the lighting equations” to a model that might be distributed
to the public. It would be up to the user of the model to
add any “light sources that participate in lighting
equations”, even if they were internal to the 3D model.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">Thanks
again,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US">Roy<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="color:windowtext"
lang="EN-US">From:</span></b><span
style="color:windowtext" lang="EN-US"> x3d-public
[<a class="moz-txt-link-freetext" href="mailto:x3d-public-bounces@web3d.org">mailto:x3d-public-bounces@web3d.org</a>] <b>On Behalf Of </b>Leonard
Daly<br>
<b>Sent:</b> 31 January 2018 18:46<br>
<b>To:</b> X3D Public <a class="moz-txt-link-rfc2396E" href="mailto:x3d-public@web3d.org"><x3d-public@web3d.org></a><br>
<b>Subject:</b> [x3d-public] Model Profile: Lights or
Not<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p>In the X3D WG call today there was a discussion of usefulness
of lights with models. Some participants contend that certain
models have lights and those need to be included with the
model. An example of this would be building lights, running
lights on vehicles, or emergency lights.<o:p></o:p></p>
<p><b>Summary: </b>Including lighting in models is not the way
the topic is taught in artistic educational institutions
throughout the world. Model lights reduces the models
usefulness -- it cannot be printed and take additional work to
use in other applications/environments.<o:p></o:p></p>
<p><o:p> </o:p></p>
<p>It is my contention that lighting is not the purview of the
completed (static or animated) model. This position is
explained and justified below based on industry development,
limitations of use, and alternatives.<o:p></o:p></p>
<p>First I wish to define a few terms:<o:p></o:p></p>
<ol start="1" type="1">
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0
level1 lfo1">Geometry - the collection of quads, triangles,
lines, points, and other surfaces that comprise all of the
geometry elements of the object. <o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0
level1 lfo1">Textures - the collection of all surface or
volume coloring. This include (flat) material, image and
volume textures, physically-based rendering (PBR), and
specialty materials usually expressed as shaders<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0
level1 lfo1">Rigging - the process of defining a skeleton
and attaching the surface to the skeleton for animation<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0
level1 lfo1">Animation - The process of defining all motions
and positions that the object may assume. This includes
predefined motions (such as walking, running, etc.) and
procedural ones. <o:p></o:p></li>
</ol>
<p>In the Model profile I explicitly excluded lighting because
lights are part of the scene. A light interacts with multiple
models and the scene environment. The scene environment also
interacts with lights (e.g., fog or mirrors). It might be
argued that certain lights that only interact with the model
could be used. Those lights would not interact with anything
else -- either another model or the scene environment. All of
the examples listed in the start of this post could interact
with the scene -- building lights with other buildings,
running lights on wet pavement, emergency lights with
everything within range.<o:p></o:p></p>
<p>Note that even small dim lighting like dash lights would
interact with anyone who gets in the vehicle, and the result
would be different depending on the texture of the person.<o:p></o:p></p>
<p>Keeping lights out of models allow models to be used in many
different situations. The WG looked at the TurboSquid site.
None of the models that were examined included (model) lights.
One person brought up the page on 11 Helpful Do's and Don'ts (<a
href="https://blog.turbosquid.com/2017/07/13/selling-3d-models-online/"
moz-do-not-send="true">https://blog.turbosquid.com/2017/07/13/selling-3d-models-online/</a>).
#2 on that list is saying "DO" prepare your file (model) with
lights and cameras. These are referring to external lighting
and static viewpoints, especially those used to construct the
model previews; these are not lights intrinsic to the model.<o:p></o:p></p>
<p>A (static) model with lights cannot be printed. The lighting
changes how various parts of the surface appear and needs to
include other changes to the environment, none of which is
available to the printer. If the interior of a model needs to
be lit, just bake the lighting into the texture. This goes for
selective/localized lights (e.g., spot lights) or
diffuse/panel lights (building windows).<o:p></o:p></p>
<p>Existing lighting equations are just approximations to what
happens in the real world. Different types of systems (ray
trace, Phong reflection, sub-surface scattering, etc.) are
used for different levels of results. The closer to "reality"
one needs, the more complex (and time-consuming) the
processing. In nearly every situation, the lighting equation
is out of control of the modeler. An assumption of a
particular kind of lighting system for rendering can severely
limit the use of the model.<o:p></o:p></p>
<p>Lighting is baked into the texture. This can be accomplished
in several different ways depending on the model requirement.
It can be done as a material with flat geometry and vertex
colors, an image texture applied to the surface, PBR (if
available), or highly-specialized materials implemented with
shader code. I have not encountered a single example where a
model absolutely must contain lights.<o:p></o:p></p>
<p><o:p> </o:p></p>
<div>
<p class="MsoNormal">-- <br>
<b><span style="font-size:13.5pt;color:#333366">Leonard Daly</span></b><span
style="color:#333366"><br>
3D Systems & Cloud Consultant<br>
LA ACM SIGGRAPH Past Chair<br>
President, Daly Realism - <i>Creating the Future</i> </span><o:p></o:p></p>
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<p><br>
</p>
<div class="moz-signature">-- <br>
<font class="tahoma,arial,helvetica san serif" color="#333366">
<font size="+1"><b>Leonard Daly</b></font><br>
3D Systems & Cloud Consultant<br>
LA ACM SIGGRAPH Past Chair<br>
President, Daly Realism - <i>Creating the Future</i>
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