with this code you should be able to mirror a feature "Extrusion3" around the XZ-Workplane
Private Sub Main
Dim oPartDoc As PartDocument = ThisApplication.ActiveDocument
Dim oPartComDef As PartComponentDefinition = oPartDoc.ComponentDefinition
'Dim oFeatures As Features = oPartComDef.Features
Dim oCollection As ObjectCollection
oCollection = ThisApplication.TransientObjects.CreateObjectCollection
'this is the XZ-plane
Dim oPartPlane1 As WorkPlane
oPartPlane1 = oPartComDef.WorkPlanes.Item(2)
'put a feature (or more) in the object collection
oCollection.Add(oPartComDef.Features("Extrusion3"))
'create a mirror definition
Dim mirrorDefinition As MirrorFeatureDefinition
mirrorDefinition = oPartComDef.Features.MirrorFeatures.CreateDefinition(oCollection, oPartPlane1, PatternComputeTypeEnum.kIdenticalCompute)
'create the feature
Dim mirfeature As Inventor.MirrorFeature
mirfeature = oPartComDef.Features.MirrorFeatures.AddByDefinition(mirrorDefinition)
End Sub
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Succes on your project, and have a nice day
Herm Jan