For a line, it will intersect with mask for several points, then I want to calculate the intersection point.
mask = np.zeros([300, 300, 50])
mask[:, :, 10:30] = 1
Then, the line is:
p1 = [100, 100, -1]
p2 = [100, 100, 1]
The intersection point should be:
[100, 100, 0] and [100, 100, 49].
How to implement this function with vtk?
Look at the methods in vtkLine. For example, vtkLine::DistanceToLine()
Hi Zhang, did you have a typo in your question?
It seems like
mask[:, :, 10:30] = 1
should have intersection points [100, 100, 10] and [100, 100, 29], unless I am mistaken?
Also, note that all the
IntersectWithLine() methods in VTK assume that the line is a finite line segment, and intersections never occur beyond the line’s endpoints.
Sorry for the mistake in my question, and the intersection points are [100, 100, 10] and [100, 100, 29].
IntersectWithLIne() was used to intersect a line with a mesh, but I want to intersect a line with a mask (
vtkImageData). How can I implement vtk code for this purpose?
vtkLine::DistanceToLine() is used to calculate the distance from a point to a line. But what I need is to intersect a line with a mask (
vtkImageData) and calculate the intersection point.
You are correct that
vtkImageData does not have any methods for line intersection. But I think you can do it efficiently with VTK’s clipping methods.
Here is the idea. First, use
vtkLineSource to create the line segment as a polydata, it has methods
vtkClipPolyData to clip the line segment by removing all parts of the line where the image is zero. Since
vtkClipPolyData has a
SetClipFunction() method that requires a
vtkImplicitFunction, you will have to convert the
vtkImageData to a
vtkImplicitFunction with the
vtkImplicitVolume is the class that allows you to use an image with VTK’s clipping and cutting filters.
The output of
vtkClipPolyData will be a
vtkPolyData. You can call the
vtkPolyData::GetLines() method to get the clipped line segments.
One thing you have to be careful about is that
vtkImplicitVolume generates a continuous implicit function from the image via linear interpolation, so (for example) [100,100,9] will be zero, [100,100,9.5] will be 0.5, and [100,100,10] will be 1. Make sure you understand this! So because
vtkClipPolyData will clip at zero, it will compute the intersection point to be [100,100,9] instead of [100,100,10]. The way to fix this is to use
vtkClipPolyData::SetValue(0.99999) to clip at a value just below 1.