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.

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();
    }
}

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

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