Mirror Objects Along a Plane (.NET)

With the TransformBy method of an object and the Mirroring method of a Matrix, you can mirror objects along a specified mirroring plane specified by three points.

Mirror in 3D

This example creates a box in model space. It then mirrors the box about a plane and colors the mirrored box red.

VB.NET

Imports Autodesk.AutoCAD.Runtime
Imports Autodesk.AutoCAD.ApplicationServices
Imports Autodesk.AutoCAD.DatabaseServices
Imports Autodesk.AutoCAD.Geometry
 
<CommandMethod("MirrorABox3D")> _
Public Sub MirrorABox3D()
    '' Get the current document and database, and start a transaction
    Dim acDoc As Document = Application.DocumentManager.MdiActiveDocument
    Dim acCurDb As Database = acDoc.Database

    Using acTrans As Transaction = acCurDb.TransactionManager.StartTransaction()
        '' Open the Block table for read
        Dim acBlkTbl As BlockTable
        acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId, _
                                     OpenMode.ForRead)

        '' Open the Block table record Model space for write
        Dim acBlkTblRec As BlockTableRecord
        acBlkTblRec = acTrans.GetObject(acBlkTbl(BlockTableRecord.ModelSpace), _
                                        OpenMode.ForWrite)

        '' Create a 3D solid box
        Using acSol3D As Solid3d = New Solid3d()
            acSol3D.CreateBox(5, 7, 10)

            '' Position the center of the 3D solid at (5,5,0) 
            acSol3D.TransformBy(Matrix3d.Displacement(New Point3d(5, 5, 0) - _
                                                      Point3d.Origin))

            '' Add the new object to the block table record and the transaction
            acBlkTblRec.AppendEntity(acSol3D)
            acTrans.AddNewlyCreatedDBObject(acSol3D, True)

            '' Create a copy of the original 3D solid and change the color of the copy
            Dim acSol3DCopy As Solid3d = acSol3D.Clone()
            acSol3DCopy.ColorIndex = 1

            '' Define the mirror plane
            Dim acPlane As Plane = New Plane(New Point3d(1.25, 0, 0), _
                                             New Point3d(1.25, 2, 0), _
                                             New Point3d(1.25, 2, 2))

            '' Mirror the 3D solid across the plane
            acSol3DCopy.TransformBy(Matrix3d.Mirroring(acPlane))

            '' Add the new object to the block table record and the transaction
            acBlkTblRec.AppendEntity(acSol3DCopy)
            acTrans.AddNewlyCreatedDBObject(acSol3DCopy, True)
        End Using

        '' Save the new objects to the database
        acTrans.Commit()
    End Using
End Sub

C#

using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Geometry;
 
[CommandMethod("MirrorABox3D")]
public static void MirrorABox3D()
{
    // Get the current document and database, and start a transaction
    Document acDoc = Application.DocumentManager.MdiActiveDocument;
    Database acCurDb = acDoc.Database;

    using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
    {
        // Open the Block table record for read
        BlockTable acBlkTbl;
        acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId,
                                        OpenMode.ForRead) as BlockTable;

        // Open the Block table record Model space for write
        BlockTableRecord acBlkTblRec;
        acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace],
                                        OpenMode.ForWrite) as BlockTableRecord;

        // Create a 3D solid box
        using (Solid3d acSol3D = new Solid3d())
        {
            acSol3D.CreateBox(5, 7, 10);

            // Position the center of the 3D solid at (5,5,0) 
            acSol3D.TransformBy(Matrix3d.Displacement(new Point3d(5, 5, 0) -
                                                        Point3d.Origin));

            // Add the new object to the block table record and the transaction
            acBlkTblRec.AppendEntity(acSol3D);
            acTrans.AddNewlyCreatedDBObject(acSol3D, true);

            // Create a copy of the original 3D solid and change the color of the copy
            Solid3d acSol3DCopy = acSol3D.Clone() as Solid3d;
            acSol3DCopy.ColorIndex = 1;

            // Define the mirror plane
            Plane acPlane = new Plane(new Point3d(1.25, 0, 0),
                                        new Point3d(1.25, 2, 0),
                                        new Point3d(1.25, 2, 2));

            // Mirror the 3D solid across the plane
            acSol3DCopy.TransformBy(Matrix3d.Mirroring(acPlane));

            // Add the new object to the block table record and the transaction
            acBlkTblRec.AppendEntity(acSol3DCopy);
            acTrans.AddNewlyCreatedDBObject(acSol3DCopy, true);
        }

        // Save the new objects to the database
        acTrans.Commit();
    }
}

VBA/ActiveX Code Reference

Sub MirrorABox3D()
    ' Create the box object
    Dim boxObj As Acad3DSolid
    Dim length As Double
    Dim width As Double
    Dim height As Double
    Dim center(0 To 2) As Double
    center(0) = 5#: center(1) = 5#: center(2) = 0
    length = 5#: width = 7: height = 10#
 
    ' Create the box (3DSolid) object in model space
    Set boxObj = ThisDrawing.ModelSpace. _
                     AddBox(center, length, width, height)
 
    ' Define the mirroring plane with three points
    Dim mirrorPt1(0 To 2) As Double
    Dim mirrorPt2(0 To 2) As Double
    Dim mirrorPt3(0 To 2) As Double
 
    mirrorPt1(0) = 1.25: mirrorPt1(1) = 0: mirrorPt1(2) = 0
    mirrorPt2(0) = 1.25: mirrorPt2(1) = 2: mirrorPt2(2) = 0
    mirrorPt3(0) = 1.25: mirrorPt3(1) = 2: mirrorPt3(2) = 2
 
    ' Mirror the box
    Dim mirrorBoxObj As Acad3DSolid
    Set mirrorBoxObj = boxObj.Mirror3D _
                          (mirrorPt1, mirrorPt2, mirrorPt3)
    mirrorBoxObj.Color = acRed
 
    ZoomAll
End Sub