I was wondering if there’s s script I could use to get the coordinates of my intersection point where my plane and line meet.

I would like to use this coordinate later on for angle measurements as my project involves angles measured against a plane defined by interlandmark lines.

Bing chat question: “generate python code that can compute intersection point of a line and plane in 3D”

Answer:

```
# Define a line by its direction vector and a point on it
line_dir = [1, 2, 3] # direction vector of the line
line_pt = [0, 0, 0] # a point on the line
# Define a plane by its normal vector and a point on it
plane_norm = [4, 5, 6] # normal vector of the plane
plane_pt = [1, 1, 1] # a point on the plane
# Compute the dot product of the line direction and the plane normal
dot_prod = sum([a*b for a,b in zip(line_dir, plane_norm)])
# Check if the dot product is zero, which means the line is parallel to the plane
if dot_prod == 0:
print("The line is parallel to the plane. No intersection point.")
else:
# Compute the parameter t that gives the intersection point
t = sum([(a-b)*c for a,b,c in zip(plane_pt, line_pt, plane_norm)]) / dot_prod
# Compute the intersection point by plugging t into the line equation
inter_pt = [a + b*t for a,b in zip(line_pt, line_dir)]
# Print the intersection point
print("The intersection point is", inter_pt)
```

The complete solution (setting the inputs from markupnodes and writing the result to a markup node:

```
# Get inputs from nodes
lineNode = getNode('L')
planeNode = getNode('P')
# Create output node
intersectionPointNode = slicer.mrmlScene.AddNewNodeByClass('vtkMRMLMarkupsFiducialNode', "Intersection")
import numpy as np
# Define a line by its direction vector and a point on it
line_dir = np.array(lineNode.GetLineStartPositionWorld())-np.array(lineNode.GetLineEndPositionWorld())
line_dir /= np.linalg.norm(line_dir)
line_pt = lineNode.GetLineStartPositionWorld()
# Define a plane by its normal vector and a point on it
plane_norm = planeNode.GetNormalWorld()
plane_pt = planeNode.GetOriginWorld()
###
# Compute the dot product of the line direction and the plane normal
dot_prod = sum([a*b for a,b in zip(line_dir, plane_norm)])
# Check if the dot product is zero, which means the line is parallel to the plane
if dot_prod == 0:
print("The line is parallel to the plane. No intersection point.")
else:
# Compute the parameter t that gives the intersection point
t = sum([(a-b)*c for a,b,c in zip(plane_pt, line_pt, plane_norm)]) / dot_prod
# Compute the intersection point by plugging t into the line equation
inter_pt = [a + b*t for a,b in zip(line_pt, line_dir)]
# Print the intersection point
print("The intersection point is", inter_pt)
###
# Save result into the output node
intersectionPointNode.AddControlPointWorld(inter_pt)
```

Absolute lifesaver! Thank you!