# Extracting Interpolated Curve Construction Points

Developer: RhinoScript
Summary: How to reverse engineer an interpolated curve using RhinoScript.

## Question

Is it possible to obtain the original points used when creating an interpolated curve using Rhino's InterpCrv command or RhinoScript's AddInterpCurveEx method?

If the curve has a degree of 3, then the answer is yes. Just get the curve's knots, or knot vector, and then evaluate each knot value.

## Example

The following example demonstrates how to extract an interpolated curve's original construction points.

```   Function ExtractInterpCrvPoints(curve)

' local variables
Dim points(), knots, i

' default result
ExtractInterpCrvPoints = Null

' verify the curve
If Not IsNull(curve) And Rhino.IsCurve(curve) Then

' verify the degree of the curve
If Rhino.CurveDegree(curve) = 3 Then

' get the curve's knots
knots = Rhino.CurveKnots(curve)

' verify the curve's knots
If IsArray(knots) Then

' evaluate the curve at each knot value
ReDim points(UBound(knots))
For i = 0 To UBound(knots)
points(i) = Rhino.EvaluateCurve(curve, knots(i))
Next

' cull any duplicate points
ExtractInterpCrvPoints = Rhino.CullDuplicatePoints(points)

End If

End If

End If

End Function``` 