#The visualization code in ParaView is as follows:

import vtk
import numpy as np

input = self.GetInput()
output = self.GetPolyDataOutput()

# ===================== Adjust these two parameters by yourself =====================
height  = 20    # Vertical height (up-down direction)
thickness = 5   # Lateral thickness (perpendicular to the trajectory direction)
# ====================================================================================

pts = input.GetPoints()
lines = input.GetLines()

new_pts = vtk.vtkPoints()
new_polys = vtk.vtkCellArray()

idList = vtk.vtkIdList()
lines.InitTraversal()

while lines.GetNextCell(idList):
    n = idList.GetNumberOfIds()
    for i in range(n - 1):
        # Two adjacent points
        p0 = np.array(pts.GetPoint(idList.GetId(i)))
        p1 = np.array(pts.GetPoint(idList.GetId(i+1)))

        # Trajectory direction
        dir = p1 - p0
        dir = dir / np.linalg.norm(dir) if np.linalg.norm(dir) > 1e-12 else dir

        # Construct cross-section coordinate system: lateral + vertical
        up = np.array([0, 0, 1.0])
        if abs(np.dot(dir, up)) > 0.99:
            up = np.array([1, 0, 0])

        # Lateral: thickness direction
        side = np.cross(dir, up)
        side = side / np.linalg.norm(side)
        # Vertical: height direction
        vert = np.cross(side, dir)

        # 8 corner points
        hh = height / 2
        ht = thickness / 2

        c1 = p0 - ht*side - hh*vert
        c2 = p0 + ht*side - hh*vert
        c3 = p0 + ht*side + hh*vert
        c4 = p0 - ht*side + hh*vert

        c5 = p1 - ht*side - hh*vert
        c6 = p1 + ht*side - hh*vert
        c7 = p1 + ht*side + hh*vert
        c8 = p1 - ht*side + hh*vert

        # Insert points
        base = new_pts.GetNumberOfPoints()
        new_pts.InsertNextPoint(c1)
        new_pts.InsertNextPoint(c2)
        new_pts.InsertNextPoint(c3)
        new_pts.InsertNextPoint(c4)
        new_pts.InsertNextPoint(c5)
        new_pts.InsertNextPoint(c6)
        new_pts.InsertNextPoint(c7)
        new_pts.InsertNextPoint(c8)

        # 6 faces
        quads = [
            (0,1,5,4),
            (1,2,6,5),
            (2,3,7,6),
            (3,0,4,7),
            (0,3,2,1),
            (4,5,6,7)
        ]
        for q in quads:
            quad = vtk.vtkQuad()
            pids = quad.GetPointIds()
            pids.SetId(0, base+q[0])
            pids.SetId(1, base+q[1])
            pids.SetId(2, base+q[2])
            pids.SetId(3, base+q[3])
            new_polys.InsertNextCell(quad)

output.SetPoints(new_pts)
output.SetPolys(new_polys)