Re: Curve-based family instance created in wrong location

Please try the following code (Revit 2016 API) and tell me it works

#region Namespaces

using System;
using System.Text;
using System.Linq;
using System.Xml;
using System.Reflection;
using System.ComponentModel;
using System.Collections;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Media.Imaging;
using System.Windows.Forms;
using System.IO;

using Autodesk.Revit.ApplicationServices;
using Autodesk.Revit.Attributes;

using Autodesk.Revit.DB;
using Autodesk.Revit.DB.Events;
using Autodesk.Revit.DB.Architecture;
using Autodesk.Revit.DB.Structure;
using Autodesk.Revit.DB.Mechanical;
using Autodesk.Revit.DB.Electrical;
using Autodesk.Revit.DB.Plumbing;

using Autodesk.Revit.UI;
using Autodesk.Revit.UI.Selection;
using Autodesk.Revit.UI.Events;

//using Autodesk.Revit.Collections;
using Autodesk.Revit.Exceptions;
using Autodesk.Revit.Utility;

using RvtApplication = Autodesk.Revit.ApplicationServices.Application;
using RvtDocument = Autodesk.Revit.DB.Document;

#endregion

namespace RevitAddinCS2
{
    [Transaction(TransactionMode.Manual)]
    [Regeneration(RegenerationOption.Manual)]
    public class ExtCmd : IExternalCommand
    {
        #region Cached Variables

        private static ExternalCommandData _cachedCmdData;

        public static UIApplication CachedUiApp
        {
            get
            {
                return _cachedCmdData.Application;
            }
        }

        public static RvtApplication CachedApp
        {
            get
            {
                return CachedUiApp.Application;
            }
        }

        public static RvtDocument CachedDoc
        {
            get
            {
                return CachedUiApp.ActiveUIDocument.Document;
            }
        }

        #endregion

        #region IExternalCommand Members

        public Result Execute(ExternalCommandData cmdData, ref string msg, ElementSet elemSet)
        {
            _cachedCmdData = cmdData;

            try
            {
                FamilySymbol famSym = new FilteredElementCollector(CachedDoc).OfClass(typeof(FamilySymbol)).Cast<FamilySymbol>().FirstOrDefault(q => q.Family.Name.Contains("BoxGutterVoidSweep"));

                Reference edgeRef = CachedUiApp.ActiveUIDocument.Selection.PickObject(ObjectType.Edge);
                RoofBase roof = CachedDoc.GetElement(edgeRef) as RoofBase;

                Options geoOptions = CachedDoc.Application.Create.NewGeometryOptions();
                geoOptions.DetailLevel = ViewDetailLevel.Fine;
                geoOptions.ComputeReferences = true;
                GeometryElement geoElem = roof.get_Geometry(geoOptions);
                
                Edge edge = roof.GetGeometryObjectFromReference(edgeRef) as Edge;
                Face face = null;

                foreach(GeometryObject geomobj in geoElem)
                {
                    Solid s = geomobj as Solid;
                    foreach(Face f in s.Faces)
                    {
                        foreach(EdgeArray ea in f.EdgeLoops)
                        {
                            if(ea.Cast<Edge>().ToList().Contains(edge))
                            {
                                face = f;
                                break;
                            }
                        }
                    }

                }

                
                Line line = edge.AsCurveFollowingFace(face)as Line;

                using (Transaction t = new Transaction(CachedDoc, "void"))
                {
                    t.Start();
                    famSym.Activate();
                    FamilyInstance voidInstance = CachedDoc.Create.NewFamilyInstance(face, line , famSym);
                    t.Commit();
                }
                return Result.Succeeded;
            }
            catch (Exception ex)
            {
                msg = ex.ToString();
                return Result.Failed;
            }
        }

        #endregion
    }
}