# Trimming Curves with a Circle

Developer: RhinoScript
Summary: How to trim a closed curve with a circle using RhinoScript

## Problem

I have a closed spline that is intersected by a circle. I want to open the closed spline by trimming out the section crossed by the circle. I am trying to use RhinoScript's TrimCurve method, but I am not having much success. Help!

## Solution

With TrimCurve, if the input curve is closed, then the trimming interval should decrease.

For example:

``` Option Explicit

Sub CircleTrimmer

' Local variable declarations
Dim curve, circle, ccx, ccx_t(1), interval

' Select closed curve to split
curve = Rhino.GetObject("Select closed curve to split", 4)
If IsNull(curve) Then Exit Sub
If Not Rhino.IsCurveClosed(curve) Then Exit Sub

' Select circle to split with
circle = Rhino.GetObject("Select circle to split with", 4)
If IsNull(circle) Then Exit Sub
If Not Rhino.IsCircle(circle) Then Exit Sub

' Intersect the two curves
ccx = Rhino.CurveCurveIntersection(curve, circle)
If IsNull(ccx) Then
Rhino.Print "Curve and circle do not intersect"
Exit Sub
End If

' Make sure there are only two intersection events
If UBound(ccx) <> 1 Then
Rhino.Print "Unable to split curve"
Exit Sub
End If

' Get two intersection parameters on the curve
ccx_t(0) = ccx(0,5)
ccx_t(1) = ccx(1,5)

' If the input curve is closed and the interval is decreasing,
' then the portion of the curve across the start and end of the
' curve is returned.
If ccx_t(0) < ccx_t(1) Then
interval = Array(ccx_t(1), ccx_t(0))
Else
interval = Array(ccx_t(0), ccx_t(1))
End If

' Trim the curve
Rhino.TrimCurve curve, interval

End Sub``` 