What is the Best Way to Compute a Normal of a Face in Inventor API?

By Barbara Han

There can be many ways to compute a face’s normal using the geometric information provided by the Inventor objects. However, the best way to compute a normal using the API is to use the Face.Evaluator object.

Here is a sample that iteratesthroughl faces of a SurfaceBody and output the normal vectors for the faces that are planar.

VBA sample:

Public Sub ComputePlanarFacesNormals()

    Dim oPartDoc As PartDocument

    Set oPartDoc = ThisApplication.ActiveDocument

    Dim oFaces As Faces

    Set oFaces = oPartDoc.ComponentDefinition.SurfaceBodies(1).Faces

    Dim Params(1 To 2) As Double

    Dim Normals(1 To 3) As Double

    ‘If Faces is planar, then the Normal wil be the same all over the face

    Params(1) = 0

    Params(2) = 0

    Dim index As Long

    index = 1

    Dim oFace As Face

    For Each oFace In oFaces

        ‘Ensures Face is planar

        If (TypeOf oFace.Geometry Is Plane) Then

            Call oFace.Evaluator.GetNormal(Params, Normals)

            Dim oUnitNormal As UnitVector

            Set oUnitNormal = ThisApplication.TransientGeometry.CreateUnitVector(Normals(1), Normals(2), Normals(3))

            Debug.Print "Planar Face[" & index & "] Normal: [" & oUnitNormal.X & ", " & oUnitNormal.Y & ", " & oUnitNormal.Z & "]"

            index = index + 1

        End If

    Next

End Sub

VB.NET sample: