VTK与Python实现机械臂三维模型可视化详解

Python  /  管理员 发布于 7年前   200

三维可视化系统的建立依赖于三维图形平台， 如 OpenGL、VTK、OGRE、OSG等， 传统的方法多采用OpenGL进行底层编程，即对其特有的函数进行定量操作， 需要开发人员熟悉相关函数， 从而造成了开发难度大、 周期长等问题。VTK、 ORGE、OSG等平台使用封装更好的函数简化了开发过程。下面将使用Python与VTK进行机器人上位机监控界面的快速原型开发。

　　完整的上位机程序需要有三维显示模块、机器人信息监测模块（位置/角度/速度/电量/温度/错误信息...）、通信模块（串口/USB/WIFI/蓝牙...）、控制模块等功能模块。三维显示模块主要用于实时显示机器人的姿态（或位置）信息。比如机器人上肢手臂抬起，程序界面中的虚拟机器人也会同时进行同样的动作。三维显示模块也可以用于对机器人进行控制，实现良好的人机交互。比如在三维图像界面中可以点击拾取机器人某一关节，拖拽部件(肢体)控制真实的机器人完成同样的运动。Aldebaran Robotics的图形化编程软件Choregraphe可以完成上述的一些功能对NAO机器人进行控制。

对于简单的模型可以自己编写函数进行创建，但这种方法做出来的模型过于简单不够逼真。因此可以先在SolidWorks、Blender、3DMax、Maya、Rhino等三维设计软件中建立好模型，然后导出为通用的三维文件格式，再使用VTK将其读入并进行渲染。

　　在SolidWorks等三维设计软件中设计好机器人的大臂（upperarm）和小臂（forearm），然后创建装配体如下图所示。在将装配体导出为STL文件前需要注意几点：

　　1. 当从外界读入STL类型的模型时，其会按照它内部的坐标位置进行显示，因此它的位置和大小是确定的。为了以后的定位以及移动、旋转等操作的方便，需要先在SolidWorks中创建一个坐标系。如下图所示，坐标系建立在大臂关节中心点。

　　2. 如果将装配体整体输出为一个STL文件，则导入VTK后无法控制零部件进行相对运动。因此，需要将装配体各可动部件分别导出。

在SolidWorks的另存为STL对话框中，点开输出选项卡，如下图所示。注意之前提到的几点：如果勾选“在单一文件中保存装配体的所有零部件”则会将整个装配体导出为一个STL文件，否则就是分别命名的两个STL文件；输出坐标系下拉列表中选择之前创建的坐标系1，并勾选“不要转换STL输出数据到正的坐标空间”。

下面的Python代码简单实现了一个2自由度机械臂的三维仿真，可以拖动滑块或按键盘上的方向键控制肩关节或肘关节运动。当然程序还存在一些问题有待完善...

#!/usr/bin/env python import vtkimport mathfrom vtk.util.colors import *filenames = ["upperarm.stl","forearm.stl"]dt = 1.0    # degree step in rotationangle = [0, 0] # shoulder and elbow joint anglerenWin = vtk.vtkRenderWindow()assembly = vtk.vtkAssembly()slider_shoulder = vtk.vtkSliderRepresentation2D()slider_elbow = vtk.vtkSliderRepresentation2D()actor = list() # the list of links# Customize vtkInteractorStyleTrackballCamera class MyInteractor(vtk.vtkInteractorStyleTrackballCamera):  def __init__(self,parent=None):    self.AddObserver("CharEvent",self.OnCharEvent)    self.AddObserver("KeyPressEvent",self.OnKeyPressEvent)  # Override the default key operations which currently handle trackball or joystick styles is provided  # OnChar is triggered when an ASCII key is pressed. Some basic key presses are handled here   def OnCharEvent(self,obj,event):    pass  def OnKeyPressEvent(self,obj,event):    global angle    # Get the compound key strokes for the event    key = self.GetInteractor().GetKeySym()    # Output the key that was pressed    #print "Pressed: " , key    # Handle an arrow key    if(key == "Left"):      actor[1].RotateY(-dt)          if(key == "Right"):      actor[1].RotateY(dt)          if(key == "Up"):      assembly.RotateY(-dt)      angle[0] += dt      if angle[0] >= 360.0:        angle[0] -= 360.0      slider_shoulder.SetValue(angle[0])      if(key == "Down"):      assembly.RotateY(dt)      angle[0] -= dt      if angle[0] < 0.0:        angle[0] += 360.0       slider_shoulder.SetValue(angle[0])    # Ask each renderer owned by this RenderWindow to render its image and synchronize this process    renWin.Render()    returndef LoadSTL(filename):  reader = vtk.vtkSTLReader()  reader.SetFileName(filename)  mapper = vtk.vtkPolyDataMapper() # maps polygonal data to graphics primitives  mapper.SetInputConnection(reader.GetOutputPort())  actor = vtk.vtkLODActor()   actor.SetMapper(mapper)  return actor  # represents an entity in a rendered scenedef CreateCoordinates():  # create coordinate axes in the render window  axes = vtk.vtkAxesActor()   axes.SetTotalLength(100, 100, 100) # Set the total length of the axes in 3 dimensions   # Set the type of the shaft to a cylinder:0, line:1, or user defined geometry.   axes.SetShaftType(0)   axes.SetCylinderRadius(0.02)   axes.GetXAxisCaptionActor2D().SetWidth(0.03)   axes.GetYAxisCaptionActor2D().SetWidth(0.03)   axes.GetZAxisCaptionActor2D().SetWidth(0.03)   #axes.SetAxisLabels(0) # Enable:1/disable:0 drawing the axis labels  #transform = vtk.vtkTransform()   #transform.Translate(0.0, 0.0, 0.0)  #axes.SetUserTransform(transform)  #axes.GetXAxisCaptionActor2D().GetCaptionTextProperty().SetColor(1,0,0)  #axes.GetXAxisCaptionActor2D().GetCaptionTextProperty().BoldOff() # disable text bolding  return axesdef ShoulderSliderCallback(obj,event):  sliderRepres = obj.GetRepresentation()  pos = sliderRepres.GetValue()   assembly.SetOrientation(0,-pos,0)  renWin.Render()def ElbowSliderCallback(obj,event):  sliderRepres = obj.GetRepresentation()  pos = sliderRepres.GetValue()   actor[1].SetOrientation(0,-pos,0)  renWin.Render()def ConfigSlider(sliderRep, TitleText, Yaxes):  sliderRep.SetMinimumValue(0.0)  sliderRep.SetMaximumValue(360.0)  sliderRep.SetValue(0.0) # Specify the current value for the widget  sliderRep.SetTitleText(TitleText) # Specify the label text for this widget  sliderRep.GetSliderProperty().SetColor(1,0,0) # Change the color of the knob that slides  sliderRep.GetSelectedProperty().SetColor(0,0,1) # Change the color of the knob when the mouse is held on it  sliderRep.GetTubeProperty().SetColor(1,1,0) # Change the color of the bar   sliderRep.GetCapProperty().SetColor(0,1,1) # Change the color of the ends of the bar  #sliderRep.GetTitleProperty().SetColor(1,0,0) # Change the color of the text displaying the value  # Position the first end point of the slider  sliderRep.GetPoint1Coordinate().SetCoordinateSystemToDisplay()  sliderRep.GetPoint1Coordinate().SetValue(50, Yaxes)   # Position the second end point of the slider  sliderRep.GetPoint2Coordinate().SetCoordinateSystemToDisplay()  sliderRep.GetPoint2Coordinate().SetValue(400, Yaxes)   sliderRep.SetSliderLength(0.02) # Specify the length of the slider shape.The slider length by default is 0.05  sliderRep.SetSliderWidth(0.02) # Set the width of the slider in the directions orthogonal to the slider axis  sliderRep.SetTubeWidth(0.005)  sliderRep.SetEndCapWidth(0.03)  sliderRep.ShowSliderLabelOn() # display the slider text label  sliderRep.SetLabelFormat("%.1f")  sliderWidget = vtk.vtkSliderWidget()  sliderWidget.SetRepresentation(sliderRep)  sliderWidget.SetAnimationModeToAnimate()  return sliderWidgetdef CreateGround():  # create plane source  plane = vtk.vtkPlaneSource()  plane.SetXResolution(50)  plane.SetYResolution(50)  plane.SetCenter(0,0,0)  plane.SetNormal(0,0,1)    # mapper  mapper = vtk.vtkPolyDataMapper()  mapper.SetInputConnection(plane.GetOutputPort())     # actor  actor = vtk.vtkActor()  actor.SetMapper(mapper)  actor.GetProperty().SetRepresentationToWireframe()  #actor.GetProperty().SetOpacity(0.4) # 1.0 is totally opaque and 0.0 is completely transparent  actor.GetProperty().SetColor(light_grey)  '''  # Load in the texture map. A texture is any unsigned char image.  bmpReader = vtk.vtkBMPReader()   bmpReader.SetFileName("ground_texture.bmp")   texture = vtk.vtkTexture()   texture.SetInputConnection(bmpReader.GetOutputPort())   texture.InterpolateOn()   actor.SetTexture(texture)  '''  transform = vtk.vtkTransform()  transform.Scale(2000,2000, 1)  actor.SetUserTransform(transform)  return actor  def CreateScene():  # Create a rendering window and renderer  ren = vtk.vtkRenderer()  #renWin = vtk.vtkRenderWindow()  renWin.AddRenderer(ren)  # Create a renderwindowinteractor  iren = vtk.vtkRenderWindowInteractor()  iren.SetRenderWindow(renWin)  style = MyInteractor()  style.SetDefaultRenderer(ren)  iren.SetInteractorStyle(style)  for id, file in enumerate(filenames):    actor.append(LoadSTL(file))    #actor[id].GetProperty().SetColor(blue)    r = vtk.vtkMath.Random(.4, 1.0)    g = vtk.vtkMath.Random(.4, 1.0)    b = vtk.vtkMath.Random(.4, 1.0)    actor[id].GetProperty().SetDiffuseColor(r, g, b)    actor[id].GetProperty().SetDiffuse(.8)    actor[id].GetProperty().SetSpecular(.5)    actor[id].GetProperty().SetSpecularColor(1.0,1.0,1.0)    actor[id].GetProperty().SetSpecularPower(30.0)    assembly.AddPart(actor[id])    # Add the actors to the scene    #ren.AddActor(actor[id])  # Also set the origin, position and orientation of assembly in space.  assembly.SetOrigin(0, 0, 0) # This is the point about which all rotations take place   #assembly.AddPosition(0, 0, 0)  #assembly.RotateX(45)  actor[1].SetOrigin(274, 0, 0) # initial elbow joint position  ren.AddActor(assembly)  # Add coordinates  axes = CreateCoordinates()  ren.AddActor(axes)  # Add ground  ground = CreateGround()  ren.AddActor(ground)  # Add slider to control the robot  sliderWidget_shoulder = ConfigSlider(slider_shoulder,"Shoulder Joint", 80)  sliderWidget_shoulder.SetInteractor(iren)  sliderWidget_shoulder.EnabledOn()  sliderWidget_shoulder.AddObserver("InteractionEvent", ShoulderSliderCallback)  sliderWidget_elbow = ConfigSlider(slider_elbow,"Elbow Joint", 160)  sliderWidget_elbow.SetInteractor(iren)  sliderWidget_elbow.EnabledOn()  sliderWidget_elbow.AddObserver("InteractionEvent", ElbowSliderCallback)  # Set background color  ren.SetBackground(.2, .2, .2)  # Set window size  renWin.SetSize(600, 600)  # Set up the camera to get a particular view of the scene  camera = vtk.vtkCamera()  camera.SetFocalPoint(300, 0, 0)  camera.SetPosition(300, -400, 350)  camera.ComputeViewPlaneNormal()  camera.SetViewUp(0, 1, 0)  camera.Zoom(0.4)  ren.SetActiveCamera(camera)  # Enable user interface interactor  iren.Initialize()  iren.Start()if __name__ == "__main__":  CreateScene()

下面是使用MFC搭建的机器人上位机监控平台，可以实现上述的一些基本功能。这个GIF动画使用开源软件ScreenToGif生成，非常好用！

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