# Listing the Knot Vector of a NURBS Curve

Developer: RhinoScript
Summary: Demonstrates how to print the knot vector of NURBS curve using RhinoScript

### Question

I notice that Rhino's List command will display the knot vector of a NURBs curve. How can I obtain the same information, using RhinoScript, that is displayed by this command.

The following RhinoScript sample demonstrates how to print the knot vector of a NURBs curve is a format similar to that of Rhino's List command.

``` Option Explicit

Sub ListKnotVector

Dim curve : curve = Rhino.GetObject("Select curve", 4)
If IsNull(curve) Then Exit Sub

Dim knot : knot = Rhino.CurveKnots(curve)
If Not IsArray(knot) Then
Rhino.Print "NULL knot vector"
End If

' order = degree + 1
Dim order : order = Rhino.CurveDegree(curve) + 1
If (order < 2) Then
Rhino.Print "knot vector order < 2"
End If

Dim cv_count : cv_count = Rhino.CurvePointCount(curve)
If (cv_count < order) Then
Rhino.Print "knot vector cv_count < order"
End If

Dim knot_count, i, i0, mult
If (order >= 2) And (cv_count >= order) And IsArray(knot) Then
knot_count = order + cv_count - 2
i = 0
i0 = 0
Rhino.Print "index, value, mult, delta"
While (i < knot_count)
mult = 1
Do While (i + mult < knot_count)
If (i + mult < knot_count) Then
If (knot(i) = knot(i+mult)) Then
mult = mult + 1
Else
Exit Do
End If
Else
Exit Do
End If
Loop
If (i = 0) Then
Rhino.Print CStr(i) & ", " & CStr(knot(i)) & ", " & CStr(mult)
Else
Rhino.Print CStr(i) & ", " & CStr(knot(i)) & ", " & CStr(mult) & ", " & CStr(knot(i)-knot(i0))
End If
i0 = i
i = i + mult
Wend
End If

End Sub  ``` 