Define a User Coordinate System (.NET)

You define a user coordinate system ( UCS ) object to change the location of the (0, 0, 0) origin point and the orientation of the XY plane and Z axis. You can locate and orient a UCS anywhere in 3D space, and you can define, save, and recall as many user coordinate systems as you require. Coordinate input and display are relative to the current UCS.

To indicate the origin and orientation of the UCS, you can display the UCS icon at the UCS origin point using the IconAtOrigin property of a Viewport object or the UCSICON system variable. If the UCS icon is turned on (IconVisible property) and is not displayed at the origin, it is displayed at the WCS coordinate defined by the UCSORG system variable.

You can create a new user coordinate system using the Add method of the UCSTable object. This method requires four values as input: the coordinate of the origin, a coordinate on the X and Y axes, and the name of the UCS.

Most coordinates in AutoCAD are provided in the world coordinate system (WCS). Use the GetUCSMatrix method to return the transformation matrix of a given UCS to get the equivalent WCS coordinates.

To make a UCS active, use the ActiveUCS property on the Document object. If changes are made to the active UCS, the new UCS object must be reset as the active UCS for the changes to appear. To reset the active UCS, simply call the ActiveUCS property again with the updated UCS object.

Create a new UCS, make it active, and translate the coordinates of a point into the UCS coordinates

The following example creates a new UCS and sets it as the active UCS for the drawing. It then asks the user to pick a point in the drawing, and returns both WCS and UCS coordinates for the point.

C# Example

using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Geometry;
 
[CommandMethod("NewUCS")]
public static void NewUCS()
{
    // 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 UCS table for read
        UcsTable acUCSTbl;
        acUCSTbl = acTrans.GetObject(acCurDb.UcsTableId,
                                     OpenMode.ForRead) as UcsTable;

        UcsTableRecord acUCSTblRec;

        // Check to see if the "New_UCS" UCS table record exists
        if (acUCSTbl.Has("New_UCS") == false)
        {
            acUCSTblRec = new UcsTableRecord();
            acUCSTblRec.Name = "New_UCS";

            // Open the UCSTable for write
            acTrans.GetObject(acCurDb.UcsTableId, OpenMode.ForWrite);

            // Add the new UCS table record
            acUCSTbl.Add(acUCSTblRec);
            acTrans.AddNewlyCreatedDBObject(acUCSTblRec, true);
        }
        else
        {
            acUCSTblRec = acTrans.GetObject(acUCSTbl["New_UCS"],
                                            OpenMode.ForWrite) as UcsTableRecord;
        }

        acUCSTblRec.Origin = new Point3d(4, 5, 3);
        acUCSTblRec.XAxis = new Vector3d(1, 0, 0);
        acUCSTblRec.YAxis = new Vector3d(0, 1, 0);

        // Open the active viewport
        ViewportTableRecord acVportTblRec;
        acVportTblRec = acTrans.GetObject(acDoc.Editor.ActiveViewportId,
                                          OpenMode.ForWrite) as ViewportTableRecord;

        // Display the UCS Icon at the origin of the current viewport
        acVportTblRec.IconAtOrigin = true;
        acVportTblRec.IconEnabled = true;

        // Set the UCS current
        acVportTblRec.SetUcs(acUCSTblRec.ObjectId);
        acDoc.Editor.UpdateTiledViewportsFromDatabase();

        // Display the name of the current UCS
        UcsTableRecord acUCSTblRecActive;
        acUCSTblRecActive = acTrans.GetObject(acVportTblRec.UcsName,
                                              OpenMode.ForRead) as UcsTableRecord;

        Application.ShowAlertDialog("The current UCS is: " +
                                    acUCSTblRecActive.Name);

        PromptPointResult pPtRes;
        PromptPointOptions pPtOpts = new PromptPointOptions("");

        // Prompt for a point
        pPtOpts.Message = "\nEnter a point: ";
        pPtRes = acDoc.Editor.GetPoint(pPtOpts);

        Point3d pPt3dWCS;
        Point3d pPt3dUCS;

        // If a point was entered, then translate it to the current UCS
        if (pPtRes.Status == PromptStatus.OK)
        {
            pPt3dWCS = pPtRes.Value;
            pPt3dUCS = pPtRes.Value;

            // Translate the point from the current UCS to the WCS
            Matrix3d newMatrix = new Matrix3d();
            newMatrix = Matrix3d.AlignCoordinateSystem(Point3d.Origin,
                                                        Vector3d.XAxis,
                                                        Vector3d.YAxis,
                                                        Vector3d.ZAxis,
                                                        acVportTblRec.Ucs.Origin,
                                                        acVportTblRec.Ucs.Xaxis,
                                                        acVportTblRec.Ucs.Yaxis,
                                                        acVportTblRec.Ucs.Zaxis);

            pPt3dWCS = pPt3dWCS.TransformBy(newMatrix);

            Application.ShowAlertDialog("The WCS coordinates are: \n" +
                                        pPt3dWCS.ToString() + "\n" +
                                        "The UCS coordinates are: \n" +
                                        pPt3dUCS.ToString());
        }

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