用gmsh生成三角形元素,用python读取

我试图用gmsh生成一个三角形网格,然后用python读取它,对于python部分,我使用的是meshio。但我的问题是,网格元素总是读作直线,而不是三角形。

这是我的.geo

SetFactory("OpenCASCADE");
Circle(1) = {0, 0, 0, 1, 0, 2*Pi};
Curve Loop(1) = {1};
Plane Surface(1) = {1};
Physical Curve("circle", 2) = {1};

然后我跑:

gmsh -2 circle.geo

然后得到这个网格:

有了这个python代码,我阅读了网格:

ELEMENT_TYPES = {
    "line": 2,
    "line3": 3,
    "triangle": 3,
    "quadrangle": 4,
    "tetrahedron": 4,
    "hexahedron": 8,
    "prism": 6,
    "pyramid": 5,
}

def read(self, mesh_file: str):
    msh = meshio.read(mesh_file)

    points = msh.points
    number_of_nodes = points.shape[0]
    point_index = range(number_of_nodes)
    mesh_nodes = dict(zip(point_index, points))

    elements = []
    for cell in msh.cells:
        cell_type = cell.type
        for idx, element_nodes in enumerate(cell.data, 1):

            element_nodes_coordinates = np.array([mesh_nodes[node] for node in element_nodes])

            element = Element(
                index=idx,
                type=cell_type,
                size=ELEMENT_TYPES[cell_type],
                nodes=element_nodes,
                nodes_coordinates=element_nodes_coordinates,
            )

            elements.append(element)

但我总是得到一个网格类型的线(2节点元素),我需要一个3节点的三角形网格。