This rhinoscript, developed for circulation diagrams, converts curves into variable styles of surfaced three-dimensional arrows. The arrows themselves can vary in scale, proportion, angle, and several other parameters.

Rhino Script

Option Explicit
'Script written by <David Mans>
'Script copyrighted by <Neoarchaic Design>
'Script version Sunday, June 08, 2008 1:19:49 AM

Call Main()
Sub Main()
	Dim crv: crv = Rhino.GetObjects("Select Curves", 4)
	If isNull(crv) Then Exit Sub
	Dim i
	Call Rhino.EnableRedraw(False)
	For i = 0 To uBound(crv) Step 1
		Call reparameterize(crv(i))
		Call curveArrows(crv(i), 0.5, 0.95, 90, 1)
	Next
	Call Rhino.EnableRedraw(True)
End Sub
Function curveArrows(curve, dblScale, tip, headAngle, dblType)
	curveArrows = Null
	Dim i,j, crv, crvCpy, crvDom, parameter, dis,scale, count, strProfSet
	count = 3
	ReDim frame(count), pt(count*2+1),crvProfSet(count-1), swProfSet(count-2)
	'establish dimensions 
	crvDom = Rhino.CurveDomain(curve)(1)
	parameter = array(0, crvDom * tip, crvDom * tip, crvDom)
	dis = Rhino.Distance(Rhino.EvaluateCurve(curve, crvDom * tip), Rhino.EvaluateCurve(curve, crvDom)) * dblScale
	If dblType = 1 Then
		scale = array(dis * 0.25, dis * 0.25, dis * 0.5, 0)
	ElseIf dblType = 2 Then
		scale = array(dis * 0.5, dis * 0.25, dis * 0.5, 0)
	ElseIf dblType = 3 Then
		scale = array(dis * 0.25, dis * 0.5, dis * 0.5, 0)
	Else
		scale = array(dis * 0.25, dis * 0.25, dis * 0.5, 0)
	End If
	
	j = 0
	For i = 0 To count Step 1
		frame(i) = Rhino.CurveFrame(curve, parameter(i))
		pt(j) = Rhino.PointAdd(frame(i)(0), Rhino.VectorRotate(Rhino.VectorScale(frame(i)(1), scale(i)), -headAngle, frame(0)(3)))
		j = j + 1
		
		If dblType = 4 Then
			pt(j) = frame(i)(0)
		Else
			pt(j) = Rhino.PointAdd(frame(i)(0), Rhino.VectorRotate(Rhino.VectorScale(frame(i)(1), scale(i)), headAngle, frame(0)(3)))
		End If
		j = j + 1
		If i < count Then
			crvProfSet(i) = Rhino.AddPolyline(array(pt(j - 2), frame(i)(0), pt(j - 1)))
		End If
	Next
	
	Dim ptB
	If dblType = 4 Then
		Call Rhino.AddSrfPt(array(frame(3)(0), pt(j - 4), frame(2)(0)))
	Else
		Call Rhino.AddSrfPt(array(frame(3)(0), pt(j - 4), frame(2)(0)))
		Call Rhino.AddSrfPt(array(frame(3)(0), pt(j - 3), frame(2)(0)))
	End If
	'create surfaces
	crvCpy = Rhino.CopyObject(curve)
	crv = Rhino.SplitCurve(crvCpy, crvDom * tip, True)
	For i = 0 To count - 2 Step 1
		swProfSet(i) = ("_SelID " &amp; crvProfSet(i) &amp; " ")
	Next
	strProfSet = Join(swProfSet)
	Call Rhino.Command("-_Sweep1 " &amp; "_SelID " &amp; crv(0) &amp; " " &amp; strProfSet &amp; " _Enter _Enter _Simplify=None Enter")
	Call Rhino.DeleteObjects(crvProfSet)
	Call Rhino.DeleteObjects(crv)
	
End Function
Function reparameterize(strCurveID)
	If Rhino.IsCurve(strCurveID) = True Then
		Call rhino.SelectObject(strCurveID)
		Call rhino.Command("reparameterize 0 1")
		Call rhino.UnselectAllObjects()
	End If
	If Rhino.IsSurface(strCurveID) = True Then
		Call rhino.SelectObject(strCurveID)
		Call rhino.Command("reparameterize 0 1 0 1")
		Call rhino.UnselectAllObjects()
	End If		
End Function