AeroPlygiant - Atmospheric refraction simulation and analysis

Project Info

AeroPlygiant is a C++ development tool set for investigating general optical refraction behavior associated with arbitrarily complex three-dimensional (3D) atmospheric refraction conditions.

Name

The name, AeroPlygaint, is a catenation of "aero" and "plygiant". "Aero" since pertaining to Earth's atmosphere and "plygaint" from Welsh language meaning "refraction".

Pronunciation is somewhat up for grabs. Recommended is "air-o" followed by "pluh-g-yant" (in Welsh) or something like "ply-ge-ant" (in English).

Purpose

AeroPlygiant supports analysis and simulation of basic atmospheric refraction effects such as those encountered in terrestrial surveying and airborne (and space) remote sensing applications.

Applications

In its current form, AeroPlygiant is primarily a development toolbox with which specific questions can be investigated by custom coding something using the available classes. Notwithstanding, some of the demonstration programs may be generally useful more or less as-is. E.g.

General Case: Finite element propagation

• ./demo/demoAeroPlygiant.cpp - example program that illustrates the use of the finite element ray path propagation.

• ./demo/demoHotRoad - program to simulate refraction in a survey sighting made along the edge of a road associated with a bubble of low refraction index air.

• ./demo/demoExpAtmosphere - program to simulate refracting ray path from an airborne sensor platform using nominal (very)simplified exponential decay model for Earth atmospheric index of refraction.

• ./demo/demoThickPlate - program with which to evaluate refraction path through a classic optical "thick plate".

Special Case: differential equation solutions

• demo/demoAirSoundingData.cpp - program to compute index of refraction using properties of air at different heights within the atmosphere. This demonstration computes profiles of IoR values using the both the COESA1976 standard atmospheric parameter model and also data downloaded from one of the University of WY atmospheric soundings (by reading a sounding file specified on command linke). The results of each, and the difference between them is reported.

• example program that computes solution to atmospheric refraction for ray paths between different height start and end points - i.e. classic aerial remote sensing application. The solution is based on Gyer's approach (ref theory/Papers.bib).

Theoretical developments and practice

• demo/demoIntegrate.cpp - example solution to a second order differential equation system (as practice and simple analogue for solving the much more complex equation system associated with Fermat's theorem).

Features

At the moment features include:

• Gathering of useful notes and list of references in Refraction.lyx document.

• Ability (with a bit of coding) to propagate a ray path through a refractive volume of space in which the index of refraction can vary arbitrarily in all three dimensions.

• A simple 4th order Runge Kutta integrator for solving numeric differential equation systems.

• Classes and functions for solving differential equation system (Gyer model) associated with refraction in the context of classic remote sensing applications.

Resources

Top level project/software description is in README.md (this file).

Technical/math modeling notes are contained in the document "Refraction.lyx" compatible with the Lyx document processor. This project document, along with the associated Papers.bib bibliography file provide references to various works on refraction.

Software reference documentation is generated as part of the project build process.

General Use

The demonstration program provides a good overview of these steps.

• The demoAeroPlygiant.cpp example program provides a complete example including definition of a custome index of refraction environment, then tracing and reporting a ray path.

In general producing a custom path trace involves the following steps:

• Define a refractive environment (override aply::env::IndexVolume)
• Specify initial aply::ray::Start geometry (inital condition)
• Use the aply::ray::Propagator to trace path forward
• Access aply::ray::Path data for reporting/output

Project Development Environment

The software is expressed in C++ (standard 17) and should be fairly portable. It is known to build with:

• g++ (GCC) 12.2.0 - Gnu Compiler Collection for code compilation, assembly and linking.

• CMake - Build system generator. Used to create systems for project build (CMake), testing(CTest), installation, and packaging(CPack)

Build dependencies:

• Engabra - the ENGineering Geometric AlegBRA pacakge
  • Geometric algebra library used extensively for math/geometry computations.

Development dependencies

• Doxygen - Reference document generation.

• Lyx - Document processor application that utilizes Tex/LaTex to produce print-ready quality documents in various formats.

• Ipe - Extensible drawing editor (used for producing figures for Lyx documents.

Build Info

First install the required Engabra software package.

$ sudo apt-get install ${PACKAGE_PATH}/Engabra-0.1.0-Linux.deb # Install

To build Refraction package. For example (replace specific directory names and included options as appropriate for local system).

$ # -- Compile everything (including doxygen documentation)
$ mkdir <someBuildDir> && cd <someBuildDir>
$ cmake  \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=/tmpLocal/ \
    -DCMAKE_PREFIX_PATH=/tmpLocal/ \
    /repos/AeroPlygiant
$ cmake --build . --target all -j `nproc`
$ # -- Run library unit tests
$ ctest -j `nproc`

Software Reference Documentation

Code documentation is generated with CMake which uses the the Doxygen utility program during the build process to generate HTML documentation. The resulting documentation can be viewed by e.g.:

$ <favoriteBrowser> <someBuildDir>/doc/html/index.html

Installation

Current project configuration does NOT support installation (nor package building) while CMakeLists.txt still under development. (TBD)