I'm probably too late but i just read the last replies.

The VB code to make this work with a mesh object would be something like this:

Private Sub RunScript(ByVal pto As Point3d, ByVal m As Mesh, ByVal tol As Double, ByVal maxsteps As Integer, ByRef A As Object)

 Dim ptl As New list(Of point3d)
 Dim pl As New plane(pto, vector3d.ZAxis)

 While ptl.count < maxsteps
   Dim mpt As meshpoint = m.ClosestMeshPoint(pl.origin, Double.MaxValue)
   pl = New plane(mpt.Point, m.NormalAt(mpt))
  If ptl.count > 0 AndAlso pl.OriginZ > ptl(ptl.count - 1).z Then Exit While
  ptl.add(pl.Origin)
   Dim an As Double = vector3d.VectorAngle(pl.XAxis, -vector3d.ZAxis, pl)
   pl.Rotate(an, pl.ZAxis)
   pl.Translate(pl.XAxis * tol)
 End While

 a = ptl
End Sub

Note that since mesh welding affects the mesh normals it will also affect the drainage direction.

hi all,

is anyone able to elaborate on the method to achieve this with a mesh. I am a novice when it comes to writing code directly and cant seem to work out how Vicente's code is applied to achieve the results seen at the end of the thread. I have tried copying them into a VB script component but must be missing something. Is anyone able to post a definition that makes Benjamin's original drainage script work for a mesh terrain?

Many thanks

chris

Hello everyone,

I am a total beginner with Python, Rhino and Grasshopper, but I need to model the drainage paths on a surface.

I imported a .jpg file into grasshopper and created a Surface from Points. Now I tried to use your python script to model the drainage. 

When running the script it appears the Runtime error 'terrain surface' is not defined. 

But to be honest I am not sure if I even did connect the Python component correctly with my surface and further on then imported the surface correctly into the skript. 

As I said, I am a total beginner and I would really appreciate any help.