# Measure the vertical distance from a point to a line segment

Hi, I am new to this software. I need to measure the minimum distance from a point to a line segment (aka perpendicular distance) in my measurements, but I haven’t found a suitable program that can do this, do you have any code that can help?
Sincerely to the development team!
Olivia

If you copy this code in the python interactor of Slicer, it will create a random point and a random line and calculate their distance. This assumes that the line is infinitely long, the two points are just there to define it.

``````import numpy as np

# Make sure point markup exists
fiducialNode = slicer.mrmlScene.GetFirstNodeByName("F")
if fiducialNode is None:
fiducialNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLMarkupsFiducialNode", "F")

# Make sure point markup has at least one point
if fiducialNode.GetNumberOfControlPoints() < 1:
pointCoordinates = np.random.rand(3) * 200 - 100
fiducialNode.AddControlPoint(pointCoordinates[0], pointCoordinates[1], pointCoordinates[2])

# Make sure line markup exists
lineNode = slicer.mrmlScene.GetFirstNodeByName("L")
if lineNode is None:
lineNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLMarkupsLineNode", "L")

# Make sure line markup has at least two points
if lineNode.GetNumberOfControlPoints() < 2:
pointCoordinates = np.random.rand(3) * 200 - 100
lineNode.AddControlPoint(pointCoordinates[0], pointCoordinates[1], pointCoordinates[2])
pointCoordinates = np.random.rand(3) * 200 - 100
lineNode.AddControlPoint(pointCoordinates[0], pointCoordinates[1], pointCoordinates[2])

# Get point coordinates from markups
point = np.array(fiducialNode.GetNthControlPointPositionWorld(0))
line_p1 = np.array(lineNode.GetNthControlPointPositionWorld(0))
line_p2 = np.array(lineNode.GetNthControlPointPositionWorld(1))

# Calculate distance
lineVector = line_p2 - line_p1
target = np.dot(point - line_p1, lineVector) / np.dot(lineVector, lineVector)
projectionPoint = target * lineVector + line_p1
distance = np.linalg.norm(point - projectionPoint)

print(f"Distance from point to line = {distance}")

``````
1 Like

Thank you so much for your help, I tried this and it worked. But there is a little extra request, since the points and line segments I need to measure are defined by myself on the model, is it possible to change the code so that I can substitute the points and line segments I need to measure? (Sorry for needing your help as I am very bad with computers) Sincerely thank you again!

If you change the name of the point list “F” and the name of the line “L” in the code, then it should work with any point and line.

This did work and I believe it solved my problem, thank you very much to you and the rest of the development team people.