p3d_pbrt-scenes/README.md.html

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# Overview

This repository includes a number of example scenes and
data for use with the [pbrt-v3](https://github.com/mmp/pbrt-v3) renderer,
which corresponds to the system described in the third edition of
_Physically Based Rendering_, by Matt Pharr, Wenzel Jakob, and Greg
Humphreys. (See also the [pbrt website](http://pbrt.org).)

We hope that this data will be useful to users of `pbrt`, developers making
changes to the system, and researchers in rendering. To our knowledge, all
of these scenes and data can be used fairly freely. Some data is licensed
under a Creative Commons Attribution license; see details in 
Section [Scene Credits] of this document. 

# Data Sets

In addition to example scenes, there is some useful data for use with the
system.

* [bsdfs/](bsdfs/): this directory includes a variety of bidirectional scattering
  distribution functions (BSDFs) for use with the `FourierMaterial`. See, for
  example, the [coffee-splash](coffee-splash) scene for use of such a BSDF in a scene.
  * New versions of BSDFs for use with `FourierMaterial` can be generated
    with [layerlab](https://github.com/wjakob/layerlab/).

* [lenses/](lenses/): lens description files for a handful of real-world lens
  systems, for use with the `RealisticCamera`. See the scenes
  [villa/villa-photons.pbrt](villa/villa-photons.pbrt) and
  [sanmiguel/f6-17.pbrt](sanmiguel/f6-17.pbrt) for examples of their use.

* [spds/](spds/): measured spectral power distributions for a variety of standard
  illuminants, light sources, metals, and the squares of the Macbeth color
  checker.

# Scenes

A variety of scenes are available, ranging from simple ones that show off
an individual feature of the system, to more interesting ones that
demonstrate complex lighting effects in scenes with detailed geometry and
realistic reflection models.

Scene files for many of the rendered figures in the book are included here;
for example, [dragon/f11-13.pbrt](dragon/f11-13.pbrt) corresponds to Figure
11.13 in the third edition of the book.

## Directory Organization

We've tried to organize all of the scene directories in a consistent
manner; each scene directory is self-contained, containing all of the
geometry, textures, and additional data needed to render the scene.

With a few exceptions, each `*.pbrt` file in a scene directory represents a
separate variant of the scene to be rendered (possibly with different light
source configurations, different camera positions, etc.)  Some scenes have
`geometry.pbrt`, `lights-*.pbrt` and `materials.pbrt` files that collect
common geometry and material definitions across these variants. Thus, you
should be able to just run `pbrt scene-name.pbrt` for any of the remaining
`*.pbrt` files to render the corresponding scene.

Complex triangle meshes and other complex geometry is stored in the
`geometry/` directories and texture maps are all in the respective
`textures/` directories. (Similarly, any SPDs, realistic camera lenses,
or BSDF files are stored in corresponding sub-directories.)

The [images/](images/) directory (which has a structure that parallels that
of the scene directories) has EXR and PNG files corresponding to the final
output from rendering each corresponding scene. All PNGs were generated
using the `imgtool` program from the `pbrt-v3` distribution; many had a
scale factor applied with the `--scale` command-line option, and a number
include a bit of bloom to improve visual realism (via the `--bloomlevel` 
and related command-line options.) Sometimes the corresponding `*.pbrt`
file has a comment under the `Film` directive with the command line options
that were used for `imgtool`.

## A Note about Clamped Sample Values

Some of these scenes have very difficult-to-sample light transport paths
that in turn cause high variance, which manifests itself as scattered very
bright pixels in images (often called "fireflies").  (For example, scenes
with bumpy specular surfaces that are illuminated by realistic sky environment
maps suffer from this issue when a path intersects the specular surface and
is then scattered such that it happens to intersect the sun.)

There is an option for pbrt's Film implementation that allows the user to
specify a maximum value for the luminance of any sample added to the film;
if enabled, any sample with a larger luminance has its luminance scaled
down so that it is equal to the maximum. In turn, the impact of fireflies
in images can be greatly reduced.

We have used this option for a number of challenging scenes in the
following. As such, **bias has been introduced into the the images that
pbrt generates for those scenes**. We highlight this issue for two reasons:
first, if you want to use those scenes as unbiased comparisons to another
rendering system or to your implementation of a new light transport
algorithm, it's important to be aware of this (and likely, to modify the
scene files to disable this setting). Second, if you're developing a new
light transport algorithm, these scenes provide a number of challenging
situations that current algorithms don't handle well; new algorithms that
handle them effectively would be useful contributions to rendering.

## Overview of Scenes

(##) Barcelona Pavilion

![](images/barcelona-pavilion/pavilion-day.png height="200px")

![](images/barcelona-pavilion/pavilion-night.png height="200px")

[barcelona-pavilion](barcelona-pavilion): Model of van der Rohe's classic
[Barcelona Pavilion](https://en.wikipedia.org/wiki/Barcelona_Pavilion),
including both daytime and nighttime lighting setups. In the daytime setup,
all illumination comes from a realistic sky model encoded in an HDR
environment map. The night model has a very dark sky map and a number of
area light sources; it is particularly challenging to render, as much of
the illumination travels through one or more layers of glass before hitting
a surface.

barcelona-pavilion: Thanks to [Hamza Cheggour](http://www.emirage.org), who
created this [great
model](http://www.emirage.org/2013/04/24/free-download-archviz-project-pabellon-barcelona-3d-scene-v1-2-updated/)
and made it available via a
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license.

(##) Bathroom

![](images/bathroom/bathroom.png height="200px")

[bathroom](bathroom): Modern bathroom with soft indirect lighting and
depth of field. Given the mirrors and bright wight walls, multi-bounce
indirect illumination has a substantial effect on the overall appearance
of the scene.

Thanks to "nacimus", who made this scene available under the
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license. Downloaded
from [Blendswap](http://www.blendswap.com/blends/view/73937).

(##) BMW M6

![](images/bmw-m6/bmw-m6.png height="200px")

[bmw-m6](bmw-m6): BMW M6 car (model year 2006) illuminated by a realistic
skylight model.

Thanks to Fred C. M'ule Jr. ("tyrant monkey" on BlendSwap) for this nice
car model. [CC-Zero](https://creativecommons.org/publicdomain/zero/1.0/)
(public domain) license. Downloaded from
[Blendswap](http://www.blendswap.com/blends/view/3557).

(##) Breakfast

![](images/breakfast/breakfast-lamps.png height="200px")

[breakfast](breakfast): Indoor scene with chairs around a table. One
variant of the scene has light streaming in through blinds from the side
such that most of the scene is only illuminated indirectly; finding these
indirect illumination paths can be challenging.  Another variant is only
illuminated by the lights above the table; handling the resulting light
transport through the glass light fixtures is a good challenge for many
light transport algorithms.

Thanks to "Wig42", who made this scene available under a
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license. Downloaded
from [Blendswap](http://www.blendswap.com/blends/view/75431).

(##) Buddha Fractal

![](images/buddha-fractal/buddha-fractal.png height="200px")

[buddha-fractal](buddha-fractal): Stanford Buddha model made out of Stanford Buddha
models. 25,250 instances, each with 29,890 triangles, giving a total
geometric complexity of over 750 million triangles.

Thanks for Guillermo M. Leal Llaguno for this fun variant
of the Stanford Buddha model. (Buddha model courtesy [Stanford Computer
Graphics Laboratory](http://graphics.stanford.edu/data/3Dscanrep/)).

(##) Bunny Fur

![](images/bunny-fur/f3-15.png height="200px")

[bunny-fur](bunny-fur): Stanford Bunny with fur growing out of it, modeled using the
new curve shape added to `pbrt` in the third edition of the book. Over
1.5 million curves are used.

Bunny model courtesy [Stanford Computer Graphics
Laboratory](http://graphics.stanford.edu/data/3Dscanrep/).  Environment map
thanks to [Bernhard Vogl](http://dativ.at/lightprobes/index.html).

(##) Caustic Glass

![](images/caustic-glass/f16-9c.png height="200px")

[caustic-glass](caustic-glass): A delightfully complex caustic pattern that
results from light being projected through a realistic model of a bumpy
glass.

Thanks to Simon Wendsche (https://byob.carbonmade.com/) for
the model.

(##) Chopper Titan

![](images/chopper-titan/chopper-titan.png height="200px")

[chopper-titan](chopper-titan): Shiny motorcycle sitting on a glossy
surface, illuminated by a sunset.

Thanks to julioras3d for this model;
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license. Downloaded
from [Blendswap](http://www.blendswap.com/blends/view/67726).

(##) Cloud

![White cloud](images/cloud/cloud.png height="200px")

![Smoky cloud](images/cloud/smoke.png height="200px")

[cloud](cloud): One scene with a bright white cloud, showing the effect of
multiple scattering in participating media, and another, with the same
volume density but with much more absorption, leading to a much darker
cloud.  The two images show the difference between highly-scattering and
highly-absorptive media.

Smoke dataset courtesy Duc Nguyen and Ron Fedkiw.  Skylight
environment map courtesy Nolan Goodnight.

(##) Coffee Splash

![](images/coffee-splash/splash.png height="200px")

[coffee-splash](coffee-splash): A splash of coffee in a cup with a spoon,
rendered using a complex simulated BRDF for the cup and saucer, and
multiple scattering in participating media inside the splash.

Scene thanks to "guismo";
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license.  Downloaded
from [Blendswap](http://www.blendswap.com/blends/view/56136). Environment
thanks to [Bernhard Vogl](http://dativ.at/lightprobes/index.html).

(##) Contemporary Bathroom

![](images/contemporary-bathroom/contemporary-bathroom.png height="200px")

[contemporary-bathroom](contemporary-bathroom): Another contemporary
bathroom scene. This scene is quite challenging to render without visible
noise: specular light transport by the large mirror and the 
very small area light sources surrounded by glass in the light bulbs are
difficult to render efficiently.

Scene thanks to [Mareck](http://www.studios-cad.fr/galerie.html),
[CC-Zero](https://creativecommons.org/publicdomain/zero/1.0/) (public
domain) license.  "contemporary_china" texture used for wallpaper thanks to
[Adam Charlts](http://subtlepatterns.com/contemporary-china/); texture
contrast was increased for the render. "American_walnut_pxr128" wood
texture courtesy [Pixar Animation
studios](https://community.renderman.pixar.com/article/114/library-pixar-one-twenty-eight.html),
[CC-BY](https://creativecommons.org/licenses/by/4.0/) license. Abstract
print seen in mirror based on a smoke photograph by [Vanessa
Pike-Russell](https://www.flickr.com/photos/lilcrabbygal/),
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license; the photo
was inverted and contrast was adjusted for rendering.  Hurricane image used
for photo on wall courtesy [NASA Goddard Space Flight
Center](https://www.flickr.com/photos/gsfc),
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license.

(##) Crown

![](images/crown/crown.png height="200px")

[crown](crown): Detailed model of the Austrian Imperial Crown, featuring an
accurate reflection model for the gold metal surfaces, and many gems that
refract light passing through them.

This amazing model was created by Martin Lubich (http://www.loramel.net/).

(##) Dragon

![](images/dragon/f9-3.png height="200px")

[dragon](dragon): A scanned dragon model rendered with many different materials,
showing off the visual differences between them.

Dragon model courtesy Christian Schüller.  Environment map 
thanks to [Bernhard Vogl](http://dativ.at/lightprobes/index.html).

(##) Ecosystem

![](images/ecosys/ecosys.png height="200px")

[ecosys](ecosys): Fairly complex outdoor scene with many plants and trees,
illuminated by an environment map. This scene was used for the cover image
for the first edition of _Physically Based Rendering_.

Scene from Deussen et al., [Realistic modeling and rendering of plant
ecosystems](http://dl.acm.org/citation.cfm?id=280898).

(##) Figures

[figures](figures): A variety of fairly simple scenes used for figures in the book.

(##) Ganesha

![](images/ganesha/ganesha.png height="200px")

[ganesha](ganesha): Very detailed scan of a small statue with over 4.3
million triangles, illuminated by a few area light sources.

Model scanned by Wenzel Jakob.

(##) Hair

![Curly hair](images/hair/curly-hair.png height="200px")

![Straight hair](images/hair/straight-hair.png height="200px")

[hair](hair): Hair geometry to show off the hair scattering model now
available in pbrt, as described in [The Implementation of a
Hair Scattering Model](http://pbrt.org/hair.pdf).

Many thanks to [Cem Yuskel](http://www.cemyuksel.com/) for the hair
geometry, which is licensed under a "no commercial use" license.

(##) Head

![](images/head/head.png height="200px")

[head](head): Human head model with a realistic BSSRDF, showing the effect of
subsurface scattering.

Model thanks to Infinite Realities, Inc.,
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license.  Environment
map thanks to [USC-ICT light probe image
gallery](http://gl.ict.usc.edu/Data/HighResProbes/).

(##) Killeroo

![](images/killeroos/killeroo-gold.png height="200px")

[killeroos](killeroos): The classic "killeroo" model, in a variety of settings.

Thanks to [headus](http://www.headus.com/au)/Rezard for the model.

(##) Landscape

![](images/landscape/view-0.png height="200px")

![](images/landscape/view-1.png height="200px")

![](images/landscape/view-2.png height="200px")

![](images/landscape/view-3.png height="200px")

[landscape](landscape): Very complex realistic outdoor landscape scene,
featuring 23,241 unique plant models.  Thanks to object instancing, the
scene has a total geometric complexity of 3.1 billion triangles, even
though only 24 million triangles need to be stored in memory. `view-0.pbrt`
is the cover image of the third edition of the _Physically Based Rendering_
book.

Many thanks to Jan-Walter Schliep, Burak Kahraman, and Timm
Dapper from [Laubwerk](http://www.laubwerk.com) for this amazing scene.

(##) LTE Orb

![Rough glass around gold](images/lte-orb/lte-orb-roughglass.png height="200px")

![Silver around diffuse](images/lte-orb/lte-orb-silver.png height="200px")

[lte-orb](lte-orb): Spherical orb with an inset spherical object. The
geometric structure of the shapes involved provides a useful tool for
visualizing the appearance of various materials.

Thanks to Yasutoshi Mori (@MirageYM) for this model;
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license.

(##) Measure One

![](images/measure-one/frame25.png height="200px")

![](images/measure-one/frame380.png height="200px")

[measure-one](measure-one): A number of frames converted from Beeple's
amazing [Zero-Day](https://vimeo.com/140163198) animation. Converted from
Cinema4D files downloaded from [Beeple's
website](http://www.beeple-crap.com/resources.php). (Note that the original
materials and lighting is much better--improvements to our conversion 
gratefully received!)

[License]((http://beeple-crap.com/resources.php):
"These files are available under a sort of "open source" concept. They are
intended for educational use but really can be used for whatever the fuck
you want. You don't need to credit me for whatever commercial or
non-commercial use you make of them, but if you could shout me a holla with
any project that do come from them, I'd love to see it :)"

(##) PBRT Book

![](images/pbrt-book/book.png height="200px")

[pbrt-book](pbrt-book): A realistic model of the second edition of the _Physically
Based Rendering_ book.

Thanks to Karl Li (@yiningkarlli) for this fun model.

(##) San Miguel

![](images/sanmiguel/sanmiguel.png height="200px")

[sanmiguel](sanmiguel): A complex model inspired by a hotel in San Miguel de
Allende, Mexico.

Thanks to Guillermo M. Leal Llaguno for this excellent scene.

(##) Simple

![](images/simple/anim-bluespheres.png height="200px")

[simple](simple): A variety of relatively simple scenes.

(##) Smoke Plume

![](images/smoke-plume/plume-084.png height="200px")

![](images/smoke-plume/plume-184.png height="200px")

![](images/smoke-plume/plume-284.png height="200px")

A few renderings of a smoke simulation around an obstacle using volume data
generated using the simulator published with Kim et al.'s [Wavelet
Turbulence for Fluid Simulation](https://www.cs.cornell.edu/~tedkim/wturb/)
paper.

(##) Sportscar

![](images/sportscar/sportscar.png height="200px")

[sportscar](sportscar): Sportscar model, in a variety of illumination settings,
showing off the substantial differences in overall visual appearance that
result.

Excellent model and pbrt conversion courtesy of Yasutoshi Mori (@MirageYM);
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license.  Skylight
environment maps courtesy Nolan Goodnight.

(##) SSS Dragon

![](images/sssdragon/dragon_10.png height="200px")

[sssdragon](sssdragon): Dragon model rendered with subsurface scattering,
where multiple scene description files show the visual effect of changing
the density of the scattering medium.

Dragon model courtesy [Stanford Computer Graphics
Laboratory](http://graphics.stanford.edu/data/3Dscanrep/).  Environment map
thanks to [Bernhard Vogl](http://dativ.at/lightprobes/index.html).

(##) StructureSynth

![](images/structuresynth/arcsphere.png height="200px")

[structuresynth](structuresynth): A few interesting procedural scenes scenes converted
from [Structure Synth](http://structuresynth.sourceforge.net) into
`pbrt`'s format.

Environment map thanks to [USC-ICT light probe image
gallery](http://gl.ict.usc.edu/Data/HighResProbes/).

(##) Transparent Machines

![](images/transparent-machines/frame888.png height="200px")

![](images/transparent-machines/frame542.png height="200px")

[transparent-machines](transparent-machines): A variety of highly detailed
glass shapes illuminated by skylight. For good results, upwards of 64 ray
bounces are required.

Models from frames of [@beeple](http://beeple-crap.com)'s amazing
[Transparent Machines
video](https://vimeo.com/78716671). [License]((http://beeple-crap.com/resources.php):
"These files are available under a sort of "open source" concept. They are
intended for educational use but really can be used for whatever the fuck
you want. You don't need to credit me for whatever commercial or
non-commercial use you make of them, but if you could shout me a holla with
any project that do come from them, I'd love to see it :)"

(##) TT Car

![](images/tt/tt.png height="200px")

[tt](tt): Audi TT car model.

Thanks for Marko Dabrovic and Mihovil Odak for the car model.  Environment
map thanks to [USC-ICT light probe image
gallery](http://gl.ict.usc.edu/Data/HighResProbes/).

(##) Veach Bidir

![](images/veach-bidir/bidir.png height="200px")

[veach-bidir](veach-bidir): A version of a classic scene with a variety of complex
types of light transport developed by Eric Veach to show the value of
bidirectional path tracing.

(##) Veach MIS

![](images/veach-mis/f14-13-mi.png height="200px")

[veach-mis](veach-mis): Another scene based on one by Eric Veach, this one showing
off the benefit of multiple importance sampling when rendering surfaces
of varying glossiness illuminated by light sources of various sizes.

(##) Villa

![](images/villa/villa-daylight.png height="200px")

[villa](villa): Modern indoor environment. The `villa-daylight.pbrt` version is
particularly tricky to render, as all of the indoor lighting comes via
specular paths from the outside through the windows.

Many thanks to Florent Boyer for this scene.  Skylight environment
map courtesy Nolan Goodnight.

(##) VW Van

![](images/vw-van/vw-van.png height="200px")

[vw-van](vw-van): Volkswagen Van, illuminated by a HDR environment map.

Model courtesy of
[Greyscalegorilla](https://greyscalegorilla.com/gsg-free-model-pack-for-cinema-4d/),
exported from Cinema4D using the [Cinema4D pbrt
exporter](https://github.com/mmp/pbrt-v3/tree/master/exporters/cinema4d).

(##) Volume Caustic

![](images/volume-caustic/caustic.png height="200px")

[volume-caustic](volume-caustic): A glass sphere in participating media, showing off a
volumetric caustic--light being focused in the scattering medium after
passing through the sphere.

(##) White Room

![](images/white-room/whiteroom-daytime.png height="200px")

![](images/white-room/whiteroom-night.png height="200px")

[white-room](white-room): Interior scene, with two illumination
configurations. The daytime variant is primarily illuminated by light
coming through the windows from the outdoors, while the nighttime version
is illuminated by the two lights in the scene.

Scene thanks to Jay Hardy,
[CC-BY](https://creativecommons.org/licenses/by/2.0/) license. Downloaded
from [Blendswap](http://www.blendswap.com/blends/view/41683).

(##) Yeah Right

![](images/yeahright/yeahright.png height="200px")

[yeahright](yeahright): An unusual and intricate form on a glossy plate.

"Interesting" shape generated by [Keenan
Crane](http://www.cs.cmu.edu/~kmcrane/Projects/ModelRepository/).
Environment map thanks to [USC-ICT light probe image
gallery](http://gl.ict.usc.edu/Data/HighResProbes/).

(##) WIP

[wip](wip): This directory has a few scenes that aren't quite ready;
renderings don't yet look great, parameters need tuning, etc. We'll try
to get to this eventually, or if you're able to get them in good shape,
please submit an update (see the following).

# Converting Scenes to pbrt's Format

Given an amazing scene in another 3D file format, there are a few
options for converting it to be used in pbrt. (We're always happy to have
help with improvements in this area!)

## Cinema 4D

The `exporters/cinema4d` directory in the pbrt-v3 distribution provides an
exporter from Cinema 4D. This exporter was developed to export the amazing
"landscape" scene that is on the book's front cover from Cinema 4D, so thus
is up to date with respect to pbrt's material models and rendering
settings. We have seen good results with using this exporter for other
Cinema 4D scenes.

## Wavefront OBJ

The pbrt-v3 distribution includes a converter from the Wavefront OBJ
format, `obj2pbrt`, that is built when the rest of the system is compiled.
To run it, provide the path to an OBJ file and a filename for a new pbrt
file:

```bash
$ obj2pbrt scene.obj scene.pbrt
```

If there is an accompanying material description file (e.g. `scene.mtl`),
the values in it will be roughly mapped to corresponding pbrt materials.
You will likely need to manually edit and tune the materials in the
generated pbrt file in order to achieve reasonably good-looking
results.

Note that OBJ files only describe scene geometry; they don't include camera
specifications or descriptions of light sources. (Thus, the generated pbrt
input file only includes shape and material specifications that you'll need
to add inside the `WorldBegin`/`WorldEnd` block of a full pbrt input file.)
Unless you have camera and light source information separately, you'll need
to specify both on your own (see "General Tips" below for some ideas about
how to do this.)

## Blender

Many very nice scenes have been modeled in
[Blender](https://www.blender.org/) and are freely available.  (See, for
example, the [BlendSwap](http://www.blendswap.com/) website for many
scenes that can be used via a Creative Commons license.) Our experience has
been that the best approach to export scenes from Blender is to use
Blender's native OBJ export (available via the File/Export menu item) and
then to use the obj2pbrt utility described above to convert to pbrt's
format.

Blender scene files may have texture maps for the scene included directly
in their `.blend` file. Choose "File/External Data/Unpack into Files" in
Blender to save those files independently on disk. (Note that if the
textures aren't PNG or TGA format, you'll need to convert to one of those
for pbrt to be able to use them.)

We would have hoped that the Blender exporter for
[LuxRender](http://www.luxrender.net) would have worked well for pbrt
(LuxRender is originally based on pbrt and still has a similar input file
format.) Unfortunately, our experience has been that exporting to OBJ and
using obj2pbrt gives a better starting point for the scene
materials. (Further, the LuxRender Blender exporter silently fails if there
aren't any lights in the scene.) We suspect that using this exporter as a
starting point for a new direct Blender to pbrt exporter might be a
worthwhile approach.

## Old Exporters

The pbrt-v2 distribution includes
[exporters](https://github.com/mmp/pbrt-v2/tree/master/exporters) for 2010
era 3DS Max (which was used for the model used for the cover image for the
second edition of the book), Blender, Mathematica, and [Structure
Synth](http://structuresynth.sourceforge.net/). All of these are very much
out of date, both due to changes over the past six years in in the systems
they exported from as well as changes in pbrt. Some of these may be useful
for developing updated exporters for the corresponding systems for pbrt-v3.

## General Tips

A scene exported using one of the above exporters is certain to not
immediately render beautifully as is. Here are some suggestions for how to
take an initial export and turn it into something that looks great.

First, you may find it useful to run

```bash
$ pbrt --toply scene.pbrt > newscene.pbrt
```

This will convert triangle meshes into more compact binary PLY files,
giving you a much smaller pbrt scene file to edit.

Next, if the exporter doesn't include camera information, the first thing
to do is to find a good view. The "environment" camera (which renders an
image in all directions) can be useful for finding a good initial position
for the camera. Keep rendering images and adjusting the camera position to
taste. (For efficiency, use as few pixel samples as you can tolerate and
learn to squint and interpret noisy renderings!) Then, you can use the
origin you've chosen as the basis for specifying a `LookAt` transformation
for a more conventional camera model.

While placing the camera, it can be helpful to have a point light source at
the camera's position. Adding a light source like the following to your
scene file does this in a way that ensures that the light moves
appropriately to wherever the camera has been placed. (You may need to
scale the intensity up or down for good results--remember the
radius-squared falloff!

```
AttributeBegin
CoordSysTransform "camera"
LightSource "point" "color I" [10 10 10]
AttributeEnd
```

Once the camera is placed, we have found that it's next useful to set up
approximate light sources. For outdoor scenes, a good HDR environment map
is often all that is needed for lighting. (You may want to consider using
`imgtool makesky` to make a realistic HDR sky environment map.)

For indoor scenes, you may want a combination of an environment map for the
outside and point and/or area light sources for interior lights. You may
find it useful to examine the scene in the modeling system that it came
from to determine which geometry corresponds to area light sources and to
try adding `AreaLightSource` properties to those. (Note that in pbrt, area
light sources only emit lights on the side that the surface normal points;
you may need a `ReverseOrientation` directive to make the light come out in
the right direction.)

Given good lighting, the next step is to tune the materials (or set them
from scratch). It can be helpful to pick a material and set it to an
extreme value (such as a "matte" material that is pure red) and render the
scene; this quickly shows which geometric models have that material
associated with it. Alternatively, consider applying this
[patch](html/mtl.patch.txt) to your pbrt source tree; after rebuilding
pbrt, if you set the `PBRT_MTL_HACK` environment variable and render the
scene, pbrt will generate a separate image for each `NamedMaterial`
in the scene, with a filename corresponding to the material name. Each
of these images will only include the objects with that material, which
makes it easier to see what's what.

As you figure out which material names correspond to what geometry, watch
for objects that are missing texture maps and add `Texture` specifications
for them and use them in the materials. (The good news is that such objects
generally do have correct texture coordinates with them, so this mostly
just works.)

# Submitting Updates

We'd love to increase the scope (and quality) of scenes available for use
with `pbrt`. If you have a nice scene in `pbrt`'s format that you'd like to
have included in this distribution, or if you have improvements to the
current set of scenes, we'd love to have them!  (Even finding additional
good camera locations for the existing scenes or generating variants of
some of the existing scenes with different lighting setups is helpful.)

We're particularly interested in adding scenes that include complex and
realistic character models as well as scenes with realistic distributions
of hair or fur.

Unfortunately, it's not possible to host large binary distributions on
github, so submitting scene updates a little more involved than sending a
pull request. There are a few options.

* For changes small enough to be sent via email, you can use 
  `git format-patch` to make a patch that we can apply and push to the
  repository. (Send the patch to authors@pbrt.org.)

* For larger changes, consider the `git bundle` command to generate a
  binary representation of the changes. Post the resulting file online
  somewhere that we can access it, send us a pointer (again,
  authors@pbrt.org), and we'll merge it.

* Finally, if you're not comfortable enough with git for those options,
  feel free to create a zip or tar file with a new scene and send us a
  pointer to it; we can take it from there.

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