VectorAtPoint

' Place analysis results in the form of vectors at each of a beam or column's analytical model curve
Dim analyticalModel As Autodesk.Revit.DB.Structure.AnalyticalElement = Nothing
Dim relManager As Autodesk.Revit.DB.Structure.AnalyticalToPhysicalAssociationManager = Autodesk.Revit.DB.Structure.AnalyticalToPhysicalAssociationManager.GetAnalyticalToPhysicalAssociationManager(doc)

If (relManager Is Nothing) Then
   Exit Sub
End If

   Dim counterpartId As ElementId = relManager.GetAssociatedElementId(familyInstance.Id)
   If (counterpartId Is Nothing) Then
   Exit Sub
End If

analyticalModel = doc.GetElement(counterpartId)

Dim curve As Curve = analyticalModel.GetCurve()
Dim transform__1 As Transform = familyInstance.GetTransform()
   Dim index As Integer = spatialFieldManager.AddSpatialFieldPrimitive(curve, Transform.Identity)

   Dim doubleList As IList(Of Double) = New List(Of Double)()
   doubleList.Add(curve.GetEndParameter(0))
   ' vectors will be at each end of the analytical model curve
   doubleList.Add(curve.GetEndParameter(1))
   Dim pointsByParameter As New FieldDomainPointsByParameter(doubleList)

   Dim xyzList As New List(Of XYZ)()
   xyzList.Add(curve.ComputeDerivatives(0, True).BasisX.Normalize())
   ' vectors will be tangent to the curve at its ends
   Dim vectorList As IList(Of VectorAtPoint) = New List(Of VectorAtPoint)()
   vectorList.Add(New VectorAtPoint(xyzList))
   xyzList.Clear()
   xyzList.Add(curve.ComputeDerivatives(1, True).BasisX.Normalize().Negate())
   vectorList.Add(New VectorAtPoint(xyzList))
   Dim fieldValues As New FieldValues(vectorList)