【VTK+增材CAM】模型切片

目的

模型切片在3D打印喷头路径规划中是非常重要的一环。实现切片的算法有很多，主流的思想是平面与模型三角面片求交得到相交的线段，再将这些线段组织连接成折线轮廓，以便接下来进行切片层内的路径规划。下文将使用VTK简单实现模型Z轴方向的平面切片。

关键函数

vtkCutte是一个用于剪切数据的过滤器。在代码中用于得到平面和模型面片求交得到的线段。

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cutter = vtk.vtkCutter()
cutter.SetInputData(polydata)
cutter.SetCutFunction(plane)
cutter.SetSortByToSortByCell()  # 按切片层数进行排序
cutter.SetValue(i, z) # 设置轮廓的值

vtkStripper是一个用于从输入线段生成折线的过滤器。在代码中用于将散乱的线段组织连接起来成为折线轮廓。

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stripper = vtk.vtkStripper()
stripper.SetInputConnection(cutter.GetOutputPort())
stripper.JoinContiguousSegmentsOn()	# 将输出的折线首尾相连成封闭轮廓
stripper.Update()

完整代码

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import vtk


def slice_vtk(polydata, layerThk):
    """slice model with VTK into layers

    :param polydata: vtkPolyData，输入模型
    :param layerThk: float，层高
    :return: 切片列表
    """
    # 平面相交切片
    plane = vtk.vtkPlane()
    cutter = vtk.vtkCutter()
    cutter.SetInputData(polydata)
    cutter.SetCutFunction(plane)
    cutter.SetSortByToSortByCell()  # 按切片层数进行排序
    _, _, _, _, zMin, zMax = polydata.GetBounds()
    i, z = 0, zMin + layerThk
    while z < zMax:
        cutter.SetValue(i, z)
        z += layerThk
        i += 1
    # 提取轮廓
    stripper = vtk.vtkStripper()
    stripper.SetInputConnection(cutter.GetOutputPort())
    stripper.JoinContiguousSegmentsOn()
    stripper.Update()

    # numberOfLines = stripper.GetOutput().GetNumberOfLines()
    points = stripper.GetOutput().GetPoints()
    cells = stripper.GetOutput().GetLines()
    cells.InitTraversal()
    indices = vtk.vtkIdList()
    lineCount = 0
    contours = []
    while cells.GetNextCell(indices):
        # print("Line {0}:".format(lineCount))
        contour = []
        for i in range(indices.GetNumberOfIds()):
            point = points.GetPoint(indices.GetId(i))
            contour.append((point[0], point[1], point[2]))
            # print("\t({0:0.6f} ,{1:0.6f}, {2:0.6f})".format(point[0], point[1], point[2]))
        contours.append(contour)
        lineCount += 1

    return stripper, contours2Layers(contours)


def contours2Layers(contours):
    layers = []
    for contour in contours:
        layer = next((c for c in layers if (contour[0][2] == c[0][0][2])), [])
        if not layer:
            layers.append(layer)
        layer.append(contour)
    return layers


def main():
    colors = vtk.vtkNamedColors()
    lineColor = colors.GetColor3d("black")
    modelColor = colors.GetColor3d("silver")
    backgroundColor = colors.GetColor3d("wheat")

    # 加载STL模型
    reader = vtk.vtkSTLReader()
    reader.SetFileName(modelFileName)
    reader.Update()

    stripper, layers = slice_vtk(reader.GetOutput(), 2)

    modelMapper = vtk.vtkPolyDataMapper()
    modelMapper.SetInputConnection(reader.GetOutputPort())

    model = vtk.vtkActor()
    model.SetMapper(modelMapper)
    model.GetProperty().SetDiffuseColor(modelColor)
    model.GetProperty().SetInterpolationToFlat()

    linesMapper = vtk.vtkPolyDataMapper()
    linesMapper.SetInputConnection(stripper.GetOutputPort())

    lines = vtk.vtkActor()
    lines.SetMapper(linesMapper)
    lines.GetProperty().SetDiffuseColor(lineColor)
    lines.GetProperty().SetLineWidth(3.)

    renderer = vtk.vtkRenderer()
    renderWindow = vtk.vtkRenderWindow()

    renderWindow.AddRenderer(renderer)
    renderWindow.SetSize(640, 480)

    interactor = vtk.vtkRenderWindowInteractor()
    interactor.SetRenderWindow(renderWindow)

    # Add the actors to the renderer.
    renderer.AddActor(model)
    renderer.AddActor(lines)
    renderer.SetBackground(backgroundColor)

    # This starts the event loop and as a side effect causes an
    # initial render.
    renderWindow.Render()
    interactor.Start()


if __name__ == "__main__":
    main()

在上面代码中，为了将得到的轮廓按照所属切片层进行归类管理，使用如下函数进行实现。

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def contours2Layers(contours):
    layers = []
    for contour in contours:
        layer = next((c for c in layers if (contour[0][2] == c[0][0][2])), [])
        if not layer:
            layers.append(layer)
        layer.append(contour)
    return layers

测试结果

image-20221201131742669

总结

对于平面切片计算，VTK官方文档中提到了vtkPlaneCutter。vtkPlaneCutter专门用于平面切割，相较于vtkCutter速度更快，且是多线程。为了提高切片算法效率，后期可尝试vtkPlaneCutter。