Set a Spline Curvature at a Specific FitPoint in Inventor API

By Barbara Han

Issue
How to set the tangent vector (curvature) of a spline at a specific FitPoint through API?

Solution
The following code sample illustrates how to get and modify the tangent vector of a spline at a specific FitPoint.

In this sample:

1. User should firstly select a spline's FitPoint through UI

2. Use API to get the tangent vector at the selected point by SketchSplineHandle.

3. Change the vector. i.e. offset it by  (0.2, 0.2)

Note: The "SketchSplineHandle" object has been introduced in the 2008 API, so this code is only supported by Inventor versions from 2008 on.

Public Sub SetSplineCurvature()
    'First select the FitPoint of interest through the UI
    Dim oFitPoint As SketchPoint
    Set oFitPoint = ThisApplication.ActiveDocument.SelectSet.item(1)
   
    'First constraint of the point is always the 'SplineFitPointConstraint'
    Dim oConstraint As SplineFitPointConstraint
    Set oConstraint = oFitPoint.Constraints.item(1)

    'Retrieves spline from the constraint
    Dim oSpline As SketchSpline
    Set oSpline = oConstraint.Spline
   
    'Creates handle
    Call oSpline.SetHandleStatus(oFitPoint, True)
   
    'Gets handle
    Dim oSplineHandle As SketchSplineHandle
    Set oSplineHandle = oSpline.GetHandle(oFitPoint)
   
    'Gets tangent vector
    Dim oTangent As UnitVector2d
    Set oTangent = oSplineHandle.Tangent
   
    'Sets tangent vector with new value
    oSplineHandle.Tangent = ThisApplication.TransientGeometry.CreateUnitVector2d(oTangent.x + 0.2, oTangent.y + 0.2)   
End Sub

VB .NET version:
public static void SetSplineCurvature()

{

    try

    {

        Inventor.Application app = (Inventor.Application)System.

    Runtime.InteropServices.Marshal.GetActiveObject("Inventor.Application");

 

        SketchPoint oFitPoint = app.ActiveDocument.SelectSet[1] as SketchPoint;

 

        SplineFitPointConstraint oConstraint = oFitPoint.Constraints[1] as SplineFitPointConstraint;

 

        //Retrieves spline from the constraint

        SketchSpline oSpline = oConstraint.Spline;

 

        //Creates handle

        oSpline.SetHandleStatus(oFitPoint, true);

 

           //Gets handle

        SketchSplineHandle oSplineHandle = oSpline.GetHandle(oFitPoint);

 

         //Gets tangent vector

        UnitVector2d oTangent = oSplineHandle.Tangent;

 

        //Sets tangent vector with new value

        oSplineHandle.Tangent = app.TransientGeometry.CreateUnitVector2d(oTangent.X + 0.2, oTangent.Y + 0.2);

    }

    catch

    {

    }

}