homog2d

Current test status:

A single-file header-only C++ library dedicated to handling 2D lines, points and homographies (2D planar transformations) in Cartesian geometry, using internally homogeneous coordinates. Also handles other geometric primitives, see full manual.

showcase1

(see other demos here)

• Language: C++17
• Home: https://github.com/skramm/homog2d
• Usage: just fetch the file homog2d.hpp, put it somewhere, and "#include" it in your source file. No build!
• Status: beta
• Author: Sebastien Kramm, first.nosp@m.name.nosp@m..last.nosp@m.name.nosp@m.@univ.nosp@m.-rou.nosp@m.en.fr
• Licence: MPLv2

Short preview:

{C++}
#include "homog2d.hpp"
using namespace h2d;
int main()
{
    Line2d l1( Point2d(10,10) );               // a line passing through (0,0) and (10,10)
    Line2d l2( Point2d(0,10), Point2d(10,0) ); // a line passing through (0,10) and (10,0)
    auto pt = l1 * l2;                         // intersection point (5,5)
    Homogr H(2,3);                             // a translation matrix
    std::cout << H * pt;                       // prints [7,8]
}

TRYME

Try the above snippet online here, or on your own Debian-style Linux box:

$ sudo apt install build-essential
$ wget https://raw.githubusercontent.com/skramm/homog2d/master/homog2d.hpp
$ wget https://raw.githubusercontent.com/skramm/homog2d/master/misc/tryme.cpp
$ g++ tryme.cpp
$ ./a.out

will print:

[7,8]

(Depending on your GCC version, you might need to add --std=c++17 to the compiler call above.)

TRYME2:

A slightly more significant file is available here, try this:

$ wget https://raw.githubusercontent.com/skramm/homog2d/master/misc/tryme2.cpp
$ g++ tryme2.cpp
$ ./a.out > tryme2.svg

It will generate this Svg file:

tryme2

News

• 2025-06-13: fresh 2.13 release, see https://github.com/skramm/homog2d/releases
• 2025-01-26: 2.12 release
• 2024-04-21: switch to C++17, enable runtime polymorphism using std::variant, see here
• 2024-03-23: added SVG "path" element import
• 2023-12-26: 2.11 release
• 2023-11-17: added doc index
• 2023-07-11: added online Doxygen-generated reference, through the great https://codedocs.xyz/ see here
• 2023-02-19: 2.10 release, see https://github.com/skramm/homog2d/releases
• 2023-02-12: added support for "big numbers" through the ttmath library, see here (preliminar!)

(see history for more)

Details

• Install: to install on your machine, copy file homog2d.hpp somewhere where your compiler can reach it, or $ sudo make install after cloning repo. This will copy that file in /usr/local/include.
• Audience: any C++ dev requiring some basic computational geometry, without the burden of large scale framework.
• Usage: see full manual, or Doxygen-generated pages online.
• Reference: once downloaded, enter $ make doc (requires Doxygen), or read online.
• A test file is provided, needs Catch2. When installed, run $ make test (or $ make testall for testing with all 3 numerical types).
• Contributing: at present, the best you can do is testing and bug/issue reporting.
• Rationale:
  • Usage simplicity, max flexibility
  • No dependency (*)
  • Modern C++, using policy-based design, tag dispatching, sfinae, ...
  • Direct bindings with other libraries (OpenCv, Boost Geometry) (optional)
• Geometric features:
  • basic primitives: points, lines, segments, circles, rectangles, polygons, ellipse,
  • planar transformation of any of these (rotation, translation, ...),
  • computing of intersection points between these,
  • enclosing determination
  • ...
• Related libraries:
  • CGAL, the reference computational geometry library.
  • Boost Geometry, a highly generic library with some overlapping features (but quite harder to use)
  • Opencv, the reference CV library, much more algorithms, but no direct support for homogeneous geometry.
  • Wykobi, has much more computational geometry features but no direct support for homogeneous geometry.

Warning: The images shown in the manual are there just there as an illustration of what the library does, but there is no rendering code included. The library provides drawing functions, that can be used to generate Svg files. An alternative is to use a supported third-party library (Opencv), but the latter is not needed to use this library.

(*): Except for some additional features, see manual.