Projection of a curve on a surface

By Balaji Ramamoorthy

Here is a sample code to project a line on to a cylindrical surface.

It creates a cylindrical surface and a line and then does the projection. The project entities are added to the database.

[CommandMethod("ProjectLine")]
static public void ProjectLineMethod()
{
    Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
    Document doc = Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
 
    ObjectId surfaceId = ObjectId.Null;
    using (Transaction tr 
                    = db.TransactionManager.StartTransaction())
    {
        BlockTable bt = tr.GetObject(
                                        db.BlockTableId, 
                                        OpenMode.ForRead
                                    ) as BlockTable;
 
        BlockTableRecord ms = tr.GetObject(
                                bt[BlockTableRecord.ModelSpace], 
                                OpenMode.ForWrite
                                    ) as BlockTableRecord;
 
        Arc arc = new Arc(  Point3d.Origin, 
                            10.0, 
                            Math.PI * 0.5, 
                            Math.PI * 1.5
                        );
        ms.AppendEntity(arc);
        tr.AddNewlyCreatedDBObject(arc, true);
 
        Line line = new Line(   Point3d.Origin, 
                                new Point3d(0.0, 10.0, 0.0)
                            );
        ms.AppendEntity(line);
        line.ColorIndex = 2;
        tr.AddNewlyCreatedDBObject(line, true);
 
        Profile3d profile = new Profile3d(arc);
        Vector3d direction = new Vector3d(0, 0, 20.0);
 
        SweepOptions sweepOptions = new SweepOptions();
 
        surfaceId = 
            Autodesk.AutoCAD.DatabaseServices.Surface.CreateExtrudedSurface
            (
                profile, 
                direction, 
                sweepOptions, 
                true
            );
        Autodesk.AutoCAD.DatabaseServices.Surface surface
            = tr.GetObject
                (
                    surfaceId, 
                    OpenMode.ForWrite
                ) as Autodesk.AutoCAD.DatabaseServices.Surface;
 
        Entity[] projectedEntities 
            = surface.ProjectOnToSurface(line, Vector3d.XAxis.Negate());
        if (projectedEntities != null)
        {
            foreach (Entity ent in projectedEntities)
            {
                ed.WriteMessage(
                    String.Format("Projected entity : {0}", 
                                    ent.GetType().ToString()));
                ent.ColorIndex = 1;
                ms.AppendEntity(ent);
                tr.AddNewlyCreatedDBObject(ent, true); 
            }
        }
        tr.Commit();
    }
}