RAVL2, Recognition And Vision Library 2

This version of Ravl2 is work in progress, implementations maybe incomplete and may change significantly.

There are still also some files not fully ported, and parts of the cmake templates that are still generic.

Goals:

• Efficient interoperability with other vision libraries such as opencv
• Port algorithms from RAVL to use new c++ idioms

Supported platforms

• Linux
• MacOS

A windows port should be possible, but is not currently supported.

Building

Pre-requisites:

• CMake 3.21 or higher
• A C++20 compatible compiler
• OpenCV 4.5 or higher
• BLAS and LAPACK libraries

The code uses many other libraries, but if not present natively they will be downloaded and built as part of the build process. See 'Dependencies.cmake' for a full list of dependencies. Some of the libraries used include:

• cereal - For serialization
• spdlog - For logging
• xtensor - For multi-dimensional arrays
• xtensor-blas - For linear algebra
• catch2 - For unit tests
• fmt - For formatting
• nlohmann_json - For json parsing
• CLI11 - For command line parsing

Project options can be found in 'ProjectOptions.cmake'.

The build itself should be straight forward:

mkdir build
cd build
cmake ..
cmake --build .

Related code

• Much of the code comes via a cmake port of the original Ravl library: https://github.com/craftit/RavlX.git
• Adapted from ccmath. the original code can be found at: https://github.com/adis300/ccmath
• The cmake setup is based on this project template: https://github.com/cpp-best-practices/cmake_template

Code structure

The code is organized into the following directories:

• cmake: Contains cmake configuration files
• data: Contains data files used by examples and tests. These are not intended to be installed with the library.
• examples: Contains example code
• scripts: Scripts for working with the project, notably autoport_ravl.sh for updating the code from the original Ravl library.
• share: Resources used by the library.
• src: Contains the source code
  • 3D: Contains 3D geometry code
  • DLib: Contains interoperability code with DLib.
  • Geometry: Affine transforms, and geometric constructions
  • Math: Contains common math, linear algebra, and optimization code
  • OpenCV: Interoperability with OpenCV
  • Pixel: Pixel and colour space handling.
  • Qt: Interoperability with Qt
  • Image: Contains image processing code
    • Segmentation: Image segmentation, boundaries, and region growing
• test: Contains unit tests

The project is intended to be documents by doxygen.

Licensing

The original Ravl code was released under LGPL. Any new code in this project is released under the MIT license.

Coding Conventions

There is a .clang-format file in the root directory that can be used to format the code.

Naming

• Scoped objects like classes and namespaces are named with CamelCase.
• Functions and variables start with lower case.
• Types such as template arguments end with a 'T'
• It is preferred that member variables are prefixed with 'm'

Argument order

The output is the first argument(s).

Library Design

Common functions

• fill(x,value) - fill x with value
• copy(x,y) - copy y to x
• clip(x,y) - Return an array x clipped to the range specified by y
• clamp(x,y) - Return a value x limited to the range specified by y
• view(x) - Return a view of x which can be used as a Ravl2 type, this view maybe reshaped without copying the data.
• access(x) - Return a reference to the data in x. Assigning to an access object has broadcast semantics.
• clone(x) - Return a deep copy of x that maybe modified without affecting the original.

Array

• The last dimension is contiguous in memory, allowing for efficient access to the data.
• The array is a view of the data, and can be reshaped without copying the data.

These are designed to be easy to construct from other containers.

• This uses a thread safe reference counted handle to the data.
• Other than the buffer the uses is responsible for coordinating access to the data.