Hi Cesar,

for 1), I am by far not expert in OpenMesh, but in principle that way:

#define DIM2

struct MyTraits : public OpenMesh::DefaultTraits

{

#ifdef DIM2

using Point = OpenMesh::Vec2d; // the default is Vec3d..

#endif //DIM2

};

using MyMesh = OpenMesh::PolyMesh_ArrayKernelT<MyTraits>;

Then you can use 2D points as you did in your example. However, I played with 2D meshes a bit but got the feeling that certain things do not work "out of the box". For 2), as you said, exporting does not work. I think only 3d export is supported, see

OpenMesh/src/OpenMesh/Core/IO/exporter/BaseExporter.hh:

virtual Vec3f point(VertexHandle _vh) const = 0;

virtual Vec3d pointd(VertexHandle _vh) const = 0;

...

Likely, you will need to provide your own custom exporter classes. If your goal is to export to VTK a 2d mesh, then you could (as a hack) work in OpenMesh with 3D points and modify the existing vtk exporter for 2D export by neglecting the z-component.

Anyway, I would also like to if some gained some experiences with 2D meshes. Cheers, M

On Thu, Aug 27, 2020 at 5:20 PM cesar.polindara-lopez@uni-due.de wrote:

Hi to all.

Before asking my question I would like to state two important things:

1. My goal is to work with 2d triangular/polygonal meshes, from which i

don't see any examples in the documentation. As a starting point I want to create and export (to a .vtk file) a simple 2d polygonal mesh, i.e. just a square. 2) I'm new to the library so this might be a rather broad/general question.

Now, here's what i have tried.

1. I've started with the tutorial "Building a cube". There i have managed

to export the mesh to a .vtk file doing the following (variable names follow from the tutorial):

//
typedef OpenMesh::IO::ExporterT<MyMesh> BaseExporter;
BaseExporter be = BaseExporter(mesh);
OpenMesh::IO::Options opt = OpenMesh::IO::Options::Default;
OpenMesh::IO::_VTKWriter_ mywriter;
mywriter.write("output.vtk",be,opt,sizeof(double));
//

2. Now i want to modify this tutorial example to have a single square. To

be clear, I want a 2d geometry, not a 3d geometry whose vertices have constant z=0 coordinate. This is how i define the mesh:

// MyMesh::VertexHandle vhandle[4]; vhandle[0] = mesh.add_vertex(MyMesh::Point(-1, -1)); vhandle[1] = mesh.add_vertex(MyMesh::Point( 1, -1)); vhandle[2] = mesh.add_vertex(MyMesh::Point( 1, 1)); vhandle[3] = mesh.add_vertex(MyMesh::Point(-1, 1));

std::vectorMyMesh::VertexHandle face_vhandles; face_vhandles.clear(); face_vhandles.push_back(vhandle[0]); face_vhandles.push_back(vhandle[1]); face_vhandles.push_back(vhandle[2]); face_vhandles.push_back(vhandle[3]); mesh.add_face(face_vhandles) //

When i try to compile the code last code i get the following error, amongst many others:

no matching function for call to ‘OpenMesh::VectorT<float, 3>::VectorT(int, int)’ vhandle[0] = mesh.add_vertex(MyMesh::Point(-1, -1));

Now, these are my questions:

1. How can i create a 2d polygonal mesh? I guess i have to give the proper

template parameter to type definition on

typedef OpenMesh::PolyMesh_ArrayKernelT<>  MyMesh;

but i don't know what to put in there exactly.

2. How is that going to affect the BaseExporter that i use to create the

.vtk file? I am asking this because i already manage to create a 2d mesh following what i found in one of the unit tests, namely unittests_polymesh_vec2i.cc, but then i cannot export the mesh following the approach i had used for the cube. So, just in case anyone would suggest that piece of code as an answer to my question.

Any thoughts or suggestions will be greatly appreciated :)

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