Difference of geometries in C++

Question

Dear all,

How can I generate a mesh resulting from the difference (or another boolean operation) of geometries in C++?

When trying the difference giving a polygon and a circle as parameters I cannot compile the program, since the class it's expecting a shared_ptr, so I've created shared pointers, but again I cannot compile:

In file included from /Users/sensei/Documents/Projects/fracture/fenicspp/fenicspp/main.cpp:24:
In file included from /Applications/FEniCS.app/Contents/Resources/include/dolfin.h:10:
In file included from /Applications/FEniCS.app/Contents/Resources/include/dolfin/common/dolfin_common.h:7:
In file included from /Applications/FEniCS.app/Contents/Resources/include/dolfin/common/defines.h:27:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:439:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/algorithm:628:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:2100:15: error: no matching constructor for initialization of 'mshr::Polygon'
              __second_(_VSTD::forward<_Args2>(_VSTD::get<_I2>(__second_args))...)
              ^         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here's my code:

    // Vector of points
    std::vector<Point> pts;
    pts.push_back(Point(  0.0,   0.0));
    pts.push_back(Point(  4.0,   0.0));
    pts.push_back(Point(  4.0,   8.0));
    pts.push_back(Point(  0.0,   8.0));
    pts.push_back(Point(  0.0,   8.0 / 2 + 0.5));
    pts.push_back(Point(  1.0,   8.0 / 2 + 0.5));
    pts.push_back(Point(  2.0,   8.0 / 4      ));
    pts.push_back(Point(  1.0,   8.0 / 2 - 0.5));
    pts.push_back(Point(  0.0,   8.0 / 2 - 0.5));

    // Polyline
    //mshr::Polygon polyline(pts);
    auto polyline = std::make_shared<mshr::Polygon>(new mshr::Polygon(pts));

    // Hole
    //mshr::Circle circle(Point(2.0, 7.0), 0.3);
    auto circle = std::make_shared<mshr::Circle>(new mshr::Circle(Point(2.0, 7.0), 0.3));

    // Difference
    mshr::CSGDifference difference(polyline, circle);

    std::cout << "> generating mesh " << std::endl;

    // Create a simple mesh
    Mesh simple;

    // Generator
    mshr::CSGCGALMeshGenerator2D generator;

    // Set patameters
    generator.parameters["mesh_resolution"] = -1.0;
    generator.parameters["cell_size"] = 1.0;

    // Mesh it!
    generator.generate(difference, simple);

How can I correct my errors? The documentation of mshr isn't complete (and in the difference says still "CSGDifference ... Create union of two geometries").

Thanks!

senseiwa · Answer 1 · May 27, 2015

So, please excuse this self-answer, but the Wiki didn't help... Instead, the source code did!

As simple as it can be, mshr works this way:

    // Polyline
    mshr::Polygon polyline(pts);

    // Hole
    mshr::Circle circle(Point(2.0, 7.0), 0.3);

    // Difference: IT IS A SHARED POINTER
    auto difference = polyline - circle;

    std::cout << "> generating mesh " << std::endl;

    // Create a simple mesh
    Mesh simple;

    // Generator
    mshr::CSGCGALMeshGenerator2D generator;

    // Set patameters
    generator.parameters["mesh_resolution"] = -1.0;
    generator.parameters["cell_size"] = 1.0;

    // Mesh it!
    generator.generate(*difference, simple);

Cheers!

Difference of geometries in C++

1 Answer