MilchRatchet / pragueskymodel

Prague Sky Model

Fork

This fork includes an implementation of an atmosphere renderer I wrote with goal of improving the atmosphere rendering in Luminary. I changed the UI so that I can compare my implementation with this model. The result is not perfect but I am not sure whether the remaining error is my fault or due to the nature of the method. Unfortunately, I don't have an implementation of the Hillaire2020 model in this. Note that while my implementation is called a path tracer, it is just a ray marcher.

Prague Sky Model

This a C++ implementation of a sky model developed at Charles University in Prague and described in

Wilkie et al. A fitted radiance and attenuation model for realistic atmospheres. ACM Transactions on Graphics (Proceedings of SIGGRAPH 2021), 40(4), 2021.

and in

Vévoda et al. A Wide Spectral Range Sky Radiance Model. Computer Graphics Forum, 41(7), 2022.

The model is provided together with a simple renderer that demonstrates its usage and allows direct generation of sky images for various parameters.

Contents

• src/PragueSkyModel.h, src/PragueSkyModel.cpp
  • the implementation of the model
  • these two files are all you need to use the model in your code
• src/PragueSkyModelTest.h
  • a very simple example implementation of a render function that creates fisheye images of the sky
  • demonstrates how to use the model
• src/PragueSkyModelTestCli.cpp
  • a command-line user interface for src/PragueSkyModelTest.h
  • multiplatform
• src/PragueSkyModelTestGui.cpp
  • a graphical user interface for src/PragueSkyModelTest.h
  • currently works on Windows with DirectX 11 and on Linux with SDL 2 and OpenGL 2
• thirdparty/tinyexr, thirdparty/miniz
  • Tiny OpenEXR image library
  • used by both user interfaces for saving results into EXR files
• thirdparty/imgui
  • Dear ImGui library and imgui-filebrowser
  • used to build the graphical user interface
• CMakeLists.txt
  • cmake file for generating project files
• LICENSE.txt
  • Apache-2.0 license file
• README.md
  • this readme

Requirements

C++ 17 is required. GUI version also requires DirectX 11 on Windows and SDL 2 with OpenGL 2 on Linux. Both CLI and GUI versions require TBB on Linux.

Usage

1. Clone the repository, run cmake and compile

   • tested on Windows 10 with Visual Studio 2022 and MSVC 19.31.31104.0 compiler
   • tested on Ubuntu 20.04 with GNU 9.3.0 compiler, SDL 2.0.10 and OpenGL 2.1

2. Download a dataset

   • the model is flexible and can work with various versions of the dataset
   • currently available:

     • Full version (2.2 GB)

       • a full version of the dataset as presented in the first paper, contains the entire range of visibilities, solar elevations, observer altitudes, and ground albedos, includes polarisation

     • Ground-level version (103 MB)

       • a smaller version of the dataset, contains only a single (zero) observer altitude, does not include polarisation

     • SWIR version (547 MB)

       • a wide spectral range version of the dataset as presented in the second paper, contains 55 (instead of 11) wavelength channels, but only a single (zero) observer altitude, includes polarisation

       	Full	Ground-level	SWIR
       visibilities	all	all	all
       solar elevations	all	all	all
       observer altitudes	all	just one (0 m)	just one (0 m)
       ground albedos	all	all	all
       wavelength channels	11 (320 - 760 nm)	11 (320 - 760 nm)	55 (280 - 2480 nm)
       transmittance	yes	yes	yes
       polarisation	yes	no	yes

3. Run the CLI version PragueSkyModelCli -dat <path_to_the_dataset>

   • this will render a default configuration
   • use option -h or --help to display this list of available options:
     • -alb ... ground albedo, valid range [0, 1], default 0.5
     • -alt ... observer altitude, valid range [0, 15000] meters, default 0 meters
     • -azi ... solar azimuth, valid range [0, 360] degrees, default 0 degrees
     • -cam ... rendered view, 0 for up-facing fisheye, 1 for side-facing fisheye
     • -chn ... output channel, 0 for sRGB with visible range, 1 - 55 for individual channels (from 280 to 2480 nm with 40 nm steps)
     • -dat ... path to the dataset, default "PragueSkyModelDataset.dat"
     • -ele ... solar elevation, valid range [-4.2, 90] degrees, default 0 degrees
     • -mod ... what quantity to output, use 0 for sky radiance, 1 for sun radiance, 2 for polarisation and 3 for transmittance, default 0
     • -out ... output file, default "test.exr"
     • -res ... square output image resolution, default 512 pixels
     • -vis ... ground level visibility, valid range [20, 131.8] kilometers, default 59.4 kilometers

4. Or run the GUI version using PragueSkyModelGui

Acknowledgments

This implementation was supported by Chaos Czech and the Intel Graphics and Visualization Institute at Charles University.