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# benoitrosa/VTK_camera_intrinsics.py Created Oct 3, 2017

Example for setting camera intrinsics in VTK using python
 import vtk import numpy as np from vtk.util import numpy_support import cv2 class Camera_VTK(): """ Example class showing how to project a 3D world coordinate onto a 2D image plane using VTK """ def __init__(self, w, h, P, K): self.w = w self.h = h self.P = P # position of 3D sphere self.K = K # Camera matrix self.f = np.array( [K[0,0], K[1,1]] ) # focal lengths self.c = K[:2,2] # principal point # projection of 3D sphere center onto the image plane self.p_im = np.dot(self.K,P.reshape(3,1)).flatten() self.p_im /= self.p_im[-1] self.init_vtk() def getImage(self): """ Render a sphere using VTK into an image, and plot the projection of that sphere onto the image plane. They should coincide """ # Set basic camera parameters in VTK cam = self.renderer.GetActiveCamera() near = 0.1 far = 1000.0 cam.SetClippingRange(near, far) # Position is at origin, looking in z direction with y down cam.SetPosition(0, 0, 0) cam.SetFocalPoint(0, 0, 1) cam.SetViewUp(0, -1, 0) w,h = self.w, self.h # Set window center for offset principal point wcx = -2.0*(self.c[0] - self.w / 2.0) / self.w wcy = 2.0*(self.c[1] - self.h / 2.0) / self.h cam.SetWindowCenter(wcx, wcy) # Set vertical view angle as a indirect way of setting the y focal distance angle = 180 / np.pi * 2.0 * np.arctan2(self.h / 2.0, self.f[1]) cam.SetViewAngle(angle) # Set the image aspect ratio as an indirect way of setting the x focal distance m = np.eye(4) aspect = self.f[1]/self.f[0] m[0,0] = 1.0/aspect t = vtk.vtkTransform() t.SetMatrix(m.flatten()) cam.SetUserTransform(t) # Render the scene into a numpy array for openCV processing self.renWin.Render() winToIm = vtk.vtkWindowToImageFilter() winToIm.SetInput(self.renWin) winToIm.Update() vtk_image = winToIm.GetOutput() width, height, _ = vtk_image.GetDimensions() vtk_array = vtk_image.GetPointData().GetScalars() components = vtk_array.GetNumberOfComponents() arr = cv2.flip(numpy_support.vtk_to_numpy(vtk_array).reshape(height, width, components), 0) arr = cv2.cvtColor(arr, cv2.COLOR_BGR2RGB) # Draw a circle at the projected place of the 3D sphere onto the image plane cv2.circle(arr,(int(self.p_im[0]),int(self.p_im[1])),5,(0,0,255),1) return arr def init_vtk(self): """ Initialize VTK actors and rendering pipeline """ self.shpereSource = vtk.vtkSphereSource() self.shpereSource.SetCenter(self.P[0],self.P[1],self.P[2]) self.shpereSource.SetRadius(1.0) self.shperemapper = vtk.vtkPolyDataMapper() self.shperemapper.SetInputConnection(self.shpereSource.GetOutputPort()) self.shpereactor = vtk.vtkActor() self.shpereactor.SetMapper(self.shperemapper) self.renderer = vtk.vtkRenderer() self.renWin = vtk.vtkRenderWindow() self.renWin.SetOffScreenRendering(1) self.renderer.AddActor(self.shpereactor) self.renderer.SetBackground(0.1, 0.2, 0.4) self.renderer.ResetCamera() self.renWin.AddRenderer(self.renderer) self.renWin.SetSize(self.w, self.h) self.renWin.Render() if __name__ == '__main__': fx = 500.0 fy = 400.0 cx = 395.0 cy = 275.0 w = 760 h = 570 K = np.array( [ [fx, 0., cx], [ 0. ,fx, cy], [0.,0.,1.]]) P = np.array([ 11.14230157 , 11.23046172 , 28.56272345]) test = Camera_VTK(w,h,P,K) arr = test.getImage() cv2.imshow("test", arr) cv2.waitKey(0)