Dear all

I would like to test if a line intersects with a triangle.

If the line is not lying in the same plane as triangle this is done easily with `vtkTriangle.IntersectWithLine()`

. But how can I detect a collision if the line is in the same plane? It looks like `vtkTriangle.IntersectWithLine()`

does not work in this case.

Here a demonstration:

```
import vtk
# Construct a triangle for this demo.
points = vtk.vtkPoints()
points.InsertNextPoint([0,0,0])
points.InsertNextPoint([1,0,0])
points.InsertNextPoint([0,1,0])
triangle = vtk.vtkTriangle()
triangle.Initialize(3, [0,1,2], points)
# Alternatively, for a poly-data source:
# cellId = 0
# triangle = source.GetCell(cellId)
# Perform intersection.
tol = 1e-7
x = [0,0,0] # Intersection.
xp = [0,0,0] # Parametric coordinates of intersection.
t = vtk.mutable(0) # Line position, 0 ≤ t ≤ 1.
subId = vtk.mutable(0) # subId? No idea what it is, usually not needed.
p0, p1 = [0,0,1],[1,1,-3] # p0 and p1 define the line.
hasIntersection = triangle.IntersectWithLine(p0, p1, tol, t, x, xp, subId)
# This returns:
# hasIntersection: 1
# t = 0.25
# x = [0.25, 0.25, 0]
# But what if the line is in the same plane as the triangle?
p0, p1 = [0.2,0.2,0],[0.5,0.5,0] # Line entirely contained in triangle
p0, p1 = [1.0,1.0,0],[-1.0,-1.0,0] # Line intersects at [0.5,0.5,0] and [0,0,0]
hasIntersection = triangle.IntersectWithLine(p0, p1, tol, t, x, xp, subId)
```

For the case where `p0`

and `p1`

lie in the same plane as the triangle, `hasIntersection`

is always 0. How can I easily deal with both situations, where the line is either in- or out-of-plane?

I also played with `vtkTriangle.EvaluatePosition()`

, but was not able to find a succinct test.