Recreate a Ellipse by changing its normal

[哀家爆]

Hello everyone,

I have some trouble recreating a Ellipse. Here's the scene, there is a Ellipse whose normal is (0,0,-1). I want to recreate the Ellipse whose normal is (0,0,1). How should I change the Ellipse's propertites?

        public static EllipticalArc2d AsEllipticalArc2d(this EllipticalArc3d ellipticalArc)
        {
            EllipticalArc2d result = null;
            if (ellipticalArc.Normal.IsEqualTo(Vector3d.ZAxis))
            {
                result = new EllipticalArc2d(ellipticalArc.Center.AsPoint2d(),
                ellipticalArc.MajorAxis.AsVector2d(), ellipticalArc.MinorAxis.AsVector2d(),
                ellipticalArc.MajorRadius, ellipticalArc.MinorRadius, ellipticalArc.StartAngle, ellipticalArc.EndAngle);
            }
            else
            {
                result = new EllipticalArc2d(ellipticalArc.Center.AsPoint2d(),
                ellipticalArc.MajorAxis.AsVector2d(), ellipticalArc.MinorAxis.AsVector2d(),
                ellipticalArc.MajorRadius, ellipticalArc.MinorRadius, ellipticalArc.StartAngle, ellipticalArc.EndAngle);
            }

            return result;
        }

But the result  appear in other quadrants.

As the upper pic shows, if the normal of Ellipse is (0,0,1)，result is right. But if the normal of Ellipse is (0,0,-1)，result is wrong. 

[R.Gerritsen4967]

What happens when you change the Start- and EndAngle when the normal is -1?

So:

result = new EllipticalArc2d(ellipticalArc.Center.AsPoint2d(),
                ellipticalArc.MajorAxis.AsVector2d(), ellipticalArc.MinorAxis.AsVector2d(),
                ellipticalArc.MajorRadius, ellipticalArc.MinorRadius, ellipticalArc.EndAngle, ellipticalArc.StartAngle);

[_gile · Accepted solution]

Hi,

This seems to work.

public static EllipticalArc3d NegateNormal(this EllipticalArc3d source) =>
    new EllipticalArc3d(
        source.Center,
        source.MajorAxis,
        source.MinorAxis.Negate(),
        source.MajorRadius,
        source.MinorRadius,
        2.0 * Math.PI - source.EndAngle,
        2.0 * Math.PI - source.StartAngle);

[_gile]

Or, to directly replace the selected ellipse:

Extension method:

public static Ellipse NegateNormal(this Ellipse source) =>
    new Ellipse(
        source.Center,
        source.Normal.Negate(),
        source.MajorAxis,
        source.RadiusRatio,
        2.0 * Math.PI - source.EndAngle,
        2.0 * Math.PI - source.StartAngle);

Testing command:

    [CommandMethod("TEST")]
    public static void Test()
    {
        var doc = Application.DocumentManager.MdiActiveDocument;
        var db = doc.Database;
        var ed = doc.Editor;
        var peo = new PromptEntityOptions("\nSelect Ellipse: ");
        peo.SetRejectMessage("\nSelected object is not an ellipse.");
        peo.AddAllowedClass(typeof(Ellipse), true);
        var per = ed.GetEntity(peo);
        if (per.Status != PromptStatus.OK)
            return;
        using (var tr = db.TransactionManager.StartTransaction())
        {
            var source = (Ellipse)tr.GetObject(per.ObjectId, OpenMode.ForWrite);
            var ellipse = source.NegateNormal();
            var curSpace = (BlockTableRecord)tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
            curSpace.AppendEntity(ellipse);
            tr.AddNewlyCreatedDBObject(ellipse, true);
            source.SwapIdWith(ellipse.ObjectId, true, true);
            source.Erase();
            tr.Commit();
        }
    }

[哀家爆]

Thanks for your reply. Your code works very well!