I using the rhinocommand(C++), As the title shows, I want to find a single face of the mesh, such as mesh vertices, vertex normal, face normals, etc.
Now I can get all the vertex coordinates and normal vectors of the mesh.

ON_3dPoint dV;
ON_3fVector N;
if (mesh->HasSynchronizedDoubleAndSinglePrecisionVertices())
dV = mesh->m_dV[i];
if (mesh->HasVertexNormals())
N = mesh->m_N[i];

But I don’t know which face the information belongs to, and the mesh of the face is a triangle or quad.

Then, I can also get the normal vector of the face, but this can only be used on the cube…

ON_3fVector fN;
if (mesh->HasFaceNormals())
fN = mesh->m_FN[i];

If you have any ideas, please give us a lot of advice.
Thank you.

Hello @dale Thank you very much for your assistance.
Next, I need to get is the normal vector of the mesh face. I have tried ON_Mesh::m_FN , but only the cube is m_FN.Count() = m_F.Count() .
I know that ON_Mesh::m_N can get the normal vector of the vertex. Maybe I want to calculate the face vector from the point vector?

If you don’t bother, I would like to ask the parameters in ON_MeshFace::GetPlaneEquation What is ON_3dPointListRef& vertex_list ?