HTRDR - Image renderer of cloudy atmospheres

HTRDR 0.1.0 is available

High Tune: RenDeRer (htrdr) is a part of the High-Tune project: it illustrates the implementation of radiative transfer algorithms in inhomogeneous media. It is actually an image renderer in the visible part of the spectrum, for scenes composed of an atmospheric gas mixture, clouds and a ground. It uses spectral data that should be provided for the pressure and temperature atmospheric vertical profile, the liquid water content in suspension within the clouds that is a result of Large Eddy Simulation computations, and the optical properties of water droplets that have been obtained from a Mie code.

htrdr evaluates the intensity incoming on each pixel of the sensor array. The underlying algorithm is based on a Monte-Carlo method: it consists in simulating a given number of optical paths originating from a camera, directed to the atmosphere, taking into account light absorption and scattering phenomena. The computation is performed over the whole visible part of the spectrum, for the three components of the CIE 1931 XYZ colorimetric space that are subsequently recombined in order to obtain the final color for each pixel, and finally the whole image of the scene as seen from the required observation position.

During the simulation, htrdr dynamically loads/unloads cloud properties and thus it can handle clouds whose data do not feat in main memory. Furthermore, in addition of a shared memory parallelism, htrdr relies on the Message Passing Interface specification to parallelise its computations in a distribute memory environment; the htrdr binary can thus be run either directly or through a MPI process launcher like mpirun.

A straight interface

CLEMENT
Image rendered with htrdr of a 10003 cloud field produced by the Meso-NH (Lafore et al 1998, Lac et al 2018) Large Eddy Model. The initial conditions and model set-up for the simulation are described in .

htrdr is a command-line tool that performs computations on input data, writes the rendered image and nothing more. No assumption is made on how input data are created excepted that they have to follow the expected file formats. In the same spirit, the output image is written in plain text, as a list of raw pixel estimations, making easier the processing of its data.

This thin interface is, by nature, particularly well suited to be extended and integrated into a any workflow. For instance, one can save the cloud properties directly in the "High-Tune: cloud properties" format (htcp) or use the les2htcp tool to convert cloud properties from NetCDF to htcp. In the same way, the output image can be post-treated through gnuplot or converted in a regular PPM image by the htpp program, and then visualised in an image viewer as for instance feh or display.

Quick start

No pre-compiled version of htrdr is provided; it must be compiled directly from its source tree. A simple way is to rely on the high_tune branch of the Star-Engine project: it provides CMake scripts that automate the download, the compilation and the installation of htrdr and its dependencies. This build procedure assumes the following prerequisites:

Build

Assuming that the aforementioned prerequisites are available, the build procedure is summed up to:

~ $ git clone -b High-Tune-0.1.0 \
    https://gitlab.com/meso-star/star-engine.git High-Tune-0.1.0
~ $ mkdir High-Tune-0.1.0/build; cd High-Tune-0.1.0/build
~/High-Tune-0.1.0/build $ cmake ../cmake
~/High-Tune-0.1.0/build $ make

Package

Once built, the htrdr installation can be packaged in an archive that can then be deployed on compatible systems, i.e. systems whose C library, NetCDF library and MPI implementation are compatibles with the ones available on the system used to build htrdr.

~/High-Tune-0.1.0/build $ make pkg
~/High-Tune-0.1.0/build $ ls package/High-Tune-0.1.0* # list packages

Run

By default htrdr is installed in the local subdirectory of High-Tune-0.1.0. Source the provided high_tune.profile file to register htrdr against the current shell.
~ $ source ~/High-Tune-0.1.0/local/etc/high_tune.profile
~ $ htrdr -h

If the AsciiDoc tool suite was installed on make invocation, the reference documentation of the htrdr program and its associated file formats should be available through man pages. Use the man command-line to consult them.

~ $ man htrdr
~ $ man htrdr-image
~ $ man htcp
~ $ man htmie

Refer to the High-Tune: Starter Pack to quickly run a htrdr rendering; this archive provides input data and scripts that are good starting points to use htrdr.

Release notes

Version 0.1

Version 0.0.4

Version 0.0.3

License

htrdr is free software released under the GPLv3+ license: GNU GPL version 3 or later. You can freely study, modify or extend it. You are also welcome to redistribute it under certain conditions; refer to the license for details.