diff --git a/src/RhinoInside.Revit.External/Extensions/RhinoCommon.cs b/src/RhinoInside.Revit.External/Extensions/RhinoCommon.cs
index 394edac60..a45d4a641 100644
--- a/src/RhinoInside.Revit.External/Extensions/RhinoCommon.cs
+++ b/src/RhinoInside.Revit.External/Extensions/RhinoCommon.cs
@@ -314,7 +314,7 @@ public PlanarBrepFace(BrepFace f)
 
       public NurbsCurve Loop
       {
-        get { if (Plane.IsValid && loop is null) loop = Curve.ProjectToPlane(Face.OuterLoop.To3dCurve()?.ToNurbsCurve(), Plane) as NurbsCurve; return loop; }
+        get { if (Plane.IsValid && loop is null) loop = Face.OuterLoop.To3dCurve().ProjectToPlane(Plane) as NurbsCurve; return loop; }
       }
       public Point3d Centroid
       {
@@ -897,6 +897,40 @@ public static IEnumerable<double> Discontinuities(this Curve curve, Continuity c
       while (curve.GetNextDiscontinuity(continuity, t, domain.T1, tol1, tol2, out t))
         yield return t;
     }
+
+    public static Curve ProjectToPlane(this Curve curve, Plane plane)
+    {
+      switch (curve)
+      {
+        case null:
+          return null;
+
+        case LineCurve line:
+          line = line.DuplicateCurve() as LineCurve;
+          line.SetStartPoint(plane.ClosestPoint(line.PointAtStart));
+          line.SetEndPoint(plane.ClosestPoint(line.PointAtEnd));
+          return line;
+
+        case PolylineCurve polyline:
+          polyline = polyline.DuplicateCurve() as PolylineCurve;
+          for(int p = 0; p < polyline.PointCount; ++p)
+            polyline.SetPoint(p, plane.ClosestPoint(polyline.Point(p)));
+          return polyline;
+
+        case ArcCurve arc:
+
+          if (arc.Arc.Plane.Normal.EpsilonEquals(plane.Normal, RhinoMath.Epsilon))
+          {
+            arc = arc.DuplicateCurve() as ArcCurve;
+            arc.Translate(plane.ClosestPoint(arc.Arc.Plane.Origin) - arc.Arc.Plane.Origin);
+            return arc;
+          }
+          else return Curve.ProjectToPlane(curve?.ToNurbsCurve(), plane);
+
+        default:
+          return Curve.ProjectToPlane(curve?.ToNurbsCurve(), plane);
+      }
+    }
   }
 
   static class SurfaceExtension
diff --git a/src/RhinoInside.Revit.GH/Components/Annotations/AddDetailLine.cs b/src/RhinoInside.Revit.GH/Components/Annotations/AddDetailLine.cs
index e2627cdc0..8ceb75123 100644
--- a/src/RhinoInside.Revit.GH/Components/Annotations/AddDetailLine.cs
+++ b/src/RhinoInside.Revit.GH/Components/Annotations/AddDetailLine.cs
@@ -82,7 +82,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
           var plane = view.DetailPlane;
           var tol = GeometryTolerance.Model;
 
-          if (Curve.ProjectToPlane(curve.ToNurbsCurve(), plane) is Curve projectedCurve)
+          if (curve.ProjectToPlane(plane) is Curve projectedCurve)
             curve = projectedCurve;
           else
             throw new Exceptions.RuntimeArgumentException("Curve", "Failed to project 'Curve' into view plane", curve);
diff --git a/src/RhinoInside.Revit.GH/Components/Annotations/AddRegion.cs b/src/RhinoInside.Revit.GH/Components/Annotations/AddRegion.cs
index 54583e073..814d1919e 100644
--- a/src/RhinoInside.Revit.GH/Components/Annotations/AddRegion.cs
+++ b/src/RhinoInside.Revit.GH/Components/Annotations/AddRegion.cs
@@ -117,7 +117,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
               throw new Exceptions.RuntimeArgumentException("Boundary", "Curve should be a valid planar, closed curve and parallel to the input view.", loop);
           }
 
-          loops = loops.Select(x => Curve.ProjectToPlane(x, viewPlane)).ToArray();
+          loops = loops.Select(x => x.ProjectToPlane(viewPlane)).ToArray();
 
           // Compute
           region = Reconstruct
diff --git a/src/RhinoInside.Revit.GH/Components/Annotations/AddRevisionCloud.cs b/src/RhinoInside.Revit.GH/Components/Annotations/AddRevisionCloud.cs
index 62b8e5701..7546b947c 100644
--- a/src/RhinoInside.Revit.GH/Components/Annotations/AddRevisionCloud.cs
+++ b/src/RhinoInside.Revit.GH/Components/Annotations/AddRevisionCloud.cs
@@ -105,7 +105,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
               throw new Exceptions.RuntimeArgumentException("Boundary", "Curve should be a valid planar, closed curve and perperdicular to the input view.", loop);
           }
 
-          loops = loops.Select(x => Curve.ProjectToPlane(x, viewPlane)).ToArray();
+          loops = loops.Select(x => x.ProjectToPlane(viewPlane)).ToArray();
 
           if (revision is null)
           {
diff --git a/src/RhinoInside.Revit.GH/Components/Annotations/Datums/Grids/AddMultiSegmentGrid.cs b/src/RhinoInside.Revit.GH/Components/Annotations/Datums/Grids/AddMultiSegmentGrid.cs
index e4ef851c1..d571ed8dc 100644
--- a/src/RhinoInside.Revit.GH/Components/Annotations/Datums/Grids/AddMultiSegmentGrid.cs
+++ b/src/RhinoInside.Revit.GH/Components/Annotations/Datums/Grids/AddMultiSegmentGrid.cs
@@ -150,7 +150,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
             var tol = GeometryTolerance.Model;
             var axisPlane = sketchPlane.Location;
 
-            curve = Curve.ProjectToPlane(curve, axisPlane);
+            curve = curve.ProjectToPlane(axisPlane);
             if (curve is null) throw new RuntimeArgumentException("Curve", "Failed to project Curve on to Work Plane.", curve);
 
             curve = curve.ToArcsAndLines(tol.VertexTolerance, 10.0 * tol.AngleTolerance, tol.ShortCurveTolerance, 0.0);
diff --git a/src/RhinoInside.Revit.GH/Components/Annotations/ReferenceElements/AddReferenceLine.cs b/src/RhinoInside.Revit.GH/Components/Annotations/ReferenceElements/AddReferenceLine.cs
index 521171e09..ae6b800cc 100644
--- a/src/RhinoInside.Revit.GH/Components/Annotations/ReferenceElements/AddReferenceLine.cs
+++ b/src/RhinoInside.Revit.GH/Components/Annotations/ReferenceElements/AddReferenceLine.cs
@@ -94,7 +94,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
           if (!curve.IsParallelToPlane(plane, tol.VertexTolerance, tol.AngleTolerance))
             throw new Exceptions.RuntimeArgumentException("Curve", $"Curve should be planar and parallel to view plane.\nTolerance is {Rhino.RhinoMath.ToDegrees(tol.AngleTolerance):N1}°", curve);
 
-          if ((curve = Curve.ProjectToPlane(curve, plane)) is null)
+          if ((curve = curve.ProjectToPlane(plane)) is null)
             throw new Exceptions.RuntimeArgumentException("Curve", "Failed to project Curve into 'Work Plane'", curve);
 
           if (curve.IsClosed || curve.PointAtStart.DistanceTo(curve.PointAtEnd) < tol.VertexTolerance)
diff --git a/src/RhinoInside.Revit.GH/Components/Element/HostObject/BoundaryProfile.cs b/src/RhinoInside.Revit.GH/Components/Element/HostObject/BoundaryProfile.cs
index 5daf68c6e..3867de532 100644
--- a/src/RhinoInside.Revit.GH/Components/Element/HostObject/BoundaryProfile.cs
+++ b/src/RhinoInside.Revit.GH/Components/Element/HostObject/BoundaryProfile.cs
@@ -140,7 +140,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
 
                   foreach (var profile in profiles.OfType<Curve>())
                   {
-                    var loop = Curve.ProjectToPlane(profile, projectionPlane);
+                    var loop = profile.ProjectToPlane(projectionPlane);
 
                     var segments = loop.TryGetPolyCurve(out var polyCurve, tol.AngleTolerance) ?
                       polyCurve.DuplicateSegments() : new Curve[] { loop };
diff --git a/src/RhinoInside.Revit.GH/Components/Element/Opening/AddOpening.cs b/src/RhinoInside.Revit.GH/Components/Element/Opening/AddOpening.cs
index 4a8f268a0..3b4734a7f 100755
--- a/src/RhinoInside.Revit.GH/Components/Element/Opening/AddOpening.cs
+++ b/src/RhinoInside.Revit.GH/Components/Element/Opening/AddOpening.cs
@@ -155,7 +155,7 @@ ARDB.Opening Reconstruct(ARDB.Opening opening, ARDB.Document doc, ARDB.HostObjec
         {
           var hostPlane = sketch.SketchPlane.GetPlane().ToPlane();
           normal = hostPlane.Normal;
-          boundary = boundary.Select(x => Curve.ProjectToPlane(x, hostPlane)).ToArray();
+          boundary = boundary.Select(x => x.ProjectToPlane(hostPlane)).ToArray();
         }
       }
 
diff --git a/src/RhinoInside.Revit.GH/Components/Element/Railing/ByCurve.cs b/src/RhinoInside.Revit.GH/Components/Element/Railing/ByCurve.cs
index 5ff4681fc..f8d481f22 100644
--- a/src/RhinoInside.Revit.GH/Components/Element/Railing/ByCurve.cs
+++ b/src/RhinoInside.Revit.GH/Components/Element/Railing/ByCurve.cs
@@ -50,7 +50,7 @@ [Optional] bool flipped
         new Point3d(0.0, 0.0, level.Value.GetElevation() * GeometryDecoder.ModelScaleFactor),
         Vector3d.ZAxis
       );
-      curve = Curve.ProjectToPlane(curve, levelPlane);
+      curve = curve.ProjectToPlane(levelPlane);
       curve = curve.Simplify(CurveSimplifyOptions.All & ~CurveSimplifyOptions.Merge, tol.VertexTolerance, tol.AngleTolerance) ?? curve;
 
       // Type
diff --git a/src/RhinoInside.Revit.GH/Components/Model/AddModelLine.cs b/src/RhinoInside.Revit.GH/Components/Model/AddModelLine.cs
index fc83fd7b9..9327838c5 100644
--- a/src/RhinoInside.Revit.GH/Components/Model/AddModelLine.cs
+++ b/src/RhinoInside.Revit.GH/Components/Model/AddModelLine.cs
@@ -96,7 +96,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
           var plane = sketchPlane.Location;
           var tol = GeometryTolerance.Model;
 
-          if (Curve.ProjectToPlane(curve.ToNurbsCurve(), plane) is Curve projectedCurve)
+          if (curve.ProjectToPlane(plane) is Curve projectedCurve)
             curve = projectedCurve;
           else
             throw new Exceptions.RuntimeArgumentException("Curve", "Failed to project 'Curve' into 'Work Plane'", curve);
diff --git a/src/RhinoInside.Revit.GH/Components/Structure/AddAnalyticalPanel-Extrusion.cs b/src/RhinoInside.Revit.GH/Components/Structure/AddAnalyticalPanel-Extrusion.cs
index 59c56fcfc..5b256c94e 100644
--- a/src/RhinoInside.Revit.GH/Components/Structure/AddAnalyticalPanel-Extrusion.cs
+++ b/src/RhinoInside.Revit.GH/Components/Structure/AddAnalyticalPanel-Extrusion.cs
@@ -121,7 +121,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
           var normal = default(ARDB.XYZ);
           if (plane.HasValue)
           {
-            curve = Curve.ProjectToPlane(curve, plane.Value) ?? curve;
+            curve = curve.ProjectToPlane(plane.Value) ?? curve;
             normal = plane.Value.Normal.ToXYZ();
           }
 
diff --git a/src/RhinoInside.Revit.GH/Components/Structure/AddBeamSystem.cs b/src/RhinoInside.Revit.GH/Components/Structure/AddBeamSystem.cs
index 8dc1fed61..540caab31 100644
--- a/src/RhinoInside.Revit.GH/Components/Structure/AddBeamSystem.cs
+++ b/src/RhinoInside.Revit.GH/Components/Structure/AddBeamSystem.cs
@@ -140,7 +140,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
                 is3D = true;
 
               if (!boundary[i].IsInPlane(sketchPlane.Location, tol.VertexTolerance))
-                boundary[i] = Curve.ProjectToPlane(boundary[i], sketchPlane.Location);
+                boundary[i] = boundary[i].ProjectToPlane(sketchPlane.Location);
 
               boundaryElevation = Interval.FromUnion(boundaryElevation, new Interval(sketchPlane.Location.OriginZ, sketchPlane.Location.OriginZ));
             }
diff --git a/src/RhinoInside.Revit.GH/Components/Structure/AddTruss.cs b/src/RhinoInside.Revit.GH/Components/Structure/AddTruss.cs
index 25bd5abbc..055bc5cf9 100644
--- a/src/RhinoInside.Revit.GH/Components/Structure/AddTruss.cs
+++ b/src/RhinoInside.Revit.GH/Components/Structure/AddTruss.cs
@@ -110,7 +110,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
           var tol = GeometryTolerance.Model;
           var plane = sketchPlane.Location;
 
-          if (Curve.ProjectToPlane(curve.ToNurbsCurve(), plane) is Curve projectedCurve)
+          if (curve.ProjectToPlane(plane) is Curve projectedCurve)
             curve = projectedCurve;
           else
             throw new Exceptions.RuntimeArgumentException("Curve", "Failed to project 'Curve' into 'Work Plane'", curve);
diff --git a/src/RhinoInside.Revit.GH/Components/Topology/AddAreaBoundaryLine.cs b/src/RhinoInside.Revit.GH/Components/Topology/AddAreaBoundaryLine.cs
index b4eb4b0bd..103add530 100644
--- a/src/RhinoInside.Revit.GH/Components/Topology/AddAreaBoundaryLine.cs
+++ b/src/RhinoInside.Revit.GH/Components/Topology/AddAreaBoundaryLine.cs
@@ -121,7 +121,7 @@ bool Reuse(ARDB.ModelCurve modelCurve, ARDB.ViewPlan view, Curve curve)
 
       using (var geometryCurve = modelCurve.GeometryCurve)
       {
-        using (var projectedCurve = Curve.ProjectToPlane(curve, levelPlane).ToCurve())
+        using (var projectedCurve = curve.ProjectToPlane(levelPlane).ToCurve())
         {
           if (!projectedCurve.IsSameKindAs(geometryCurve)) return false;
           if (!projectedCurve.AlmostEquals(geometryCurve, modelCurve.Document.Application.VertexTolerance))
@@ -137,7 +137,7 @@ ARDB.ModelCurve Create(ARDB.ViewPlan view, Curve curve)
       if (view.GenLevel is ARDB.Level level)
       {
         using (var sketchPlane = level.GetSketchPlane(ensureSketchPlane: true))
-        using (var projectedCurve = Curve.ProjectToPlane(curve, sketchPlane.GetPlane().ToPlane()))
+        using (var projectedCurve = curve.ProjectToPlane(sketchPlane.GetPlane().ToPlane()))
           return view.Document.Create.NewAreaBoundaryLine(sketchPlane, projectedCurve.ToCurve(), view);
       }
 
diff --git a/src/RhinoInside.Revit.GH/Components/Topology/AddRoomSeparatorLine.cs b/src/RhinoInside.Revit.GH/Components/Topology/AddRoomSeparatorLine.cs
index 81e5802e1..ad635efa3 100644
--- a/src/RhinoInside.Revit.GH/Components/Topology/AddRoomSeparatorLine.cs
+++ b/src/RhinoInside.Revit.GH/Components/Topology/AddRoomSeparatorLine.cs
@@ -127,7 +127,7 @@ bool Reuse(ARDB.ModelCurve roomSeparator, ARDB.ViewPlan view, Curve curve)
 
       using (var geometryCurve = roomSeparator.GeometryCurve)
       {
-        using (var projectedCurve = Curve.ProjectToPlane(curve, levelPlane).ToCurve())
+        using (var projectedCurve = curve.ProjectToPlane(levelPlane).ToCurve())
         {
           if (!projectedCurve.IsSameKindAs(geometryCurve)) return false;
           if (!projectedCurve.AlmostEquals(geometryCurve, GeometryTolerance.Internal.VertexTolerance))
@@ -143,7 +143,7 @@ ARDB.ModelCurve Create(ARDB.ViewPlan view, Curve curve)
       if (view.GenLevel is ARDB.Level level)
       {
         using (var sketchPlane = level.GetSketchPlane(ensureSketchPlane: true))
-        using (var projectedCurve = Curve.ProjectToPlane(curve, sketchPlane.GetPlane().ToPlane()))
+        using (var projectedCurve = curve.ProjectToPlane(sketchPlane.GetPlane().ToPlane()))
         using (var curveArray = new ARDB.CurveArray())
         {
           curveArray.Append(projectedCurve.ToCurve());
diff --git a/src/RhinoInside.Revit.GH/Components/Topology/AddSpaceSeparatorLine.cs b/src/RhinoInside.Revit.GH/Components/Topology/AddSpaceSeparatorLine.cs
index 1b9fbdf2e..77d25cb5e 100644
--- a/src/RhinoInside.Revit.GH/Components/Topology/AddSpaceSeparatorLine.cs
+++ b/src/RhinoInside.Revit.GH/Components/Topology/AddSpaceSeparatorLine.cs
@@ -126,7 +126,7 @@ bool Reuse(ARDB.ModelCurve spaceSeparator, ARDB.ViewPlan view, Curve curve)
 
       using (var geometryCurve = spaceSeparator.GeometryCurve)
       {
-        using (var projectedCurve = Curve.ProjectToPlane(curve, levelPlane).ToCurve())
+        using (var projectedCurve = curve.ProjectToPlane(levelPlane).ToCurve())
         {
           if (!projectedCurve.IsSameKindAs(geometryCurve)) return false;
           if (!projectedCurve.AlmostEquals(geometryCurve, GeometryTolerance.Internal.VertexTolerance))
@@ -142,7 +142,7 @@ ARDB.ModelCurve Create(ARDB.ViewPlan view, Curve curve)
       if (view.GenLevel is ARDB.Level level)
       {
         using (var sketchPlane = level.GetSketchPlane(ensureSketchPlane: true))
-        using (var projectedCurve = Curve.ProjectToPlane(curve, sketchPlane.GetPlane().ToPlane()))
+        using (var projectedCurve = curve.ProjectToPlane(sketchPlane.GetPlane().ToPlane()))
         using (var curveArray = new ARDB.CurveArray())
         {
           curveArray.Append(projectedCurve.ToCurve());
diff --git a/src/RhinoInside.Revit.GH/Components/TransactionBaseComponent.cs b/src/RhinoInside.Revit.GH/Components/TransactionBaseComponent.cs
index dcefda01f..f69a647e8 100755
--- a/src/RhinoInside.Revit.GH/Components/TransactionBaseComponent.cs
+++ b/src/RhinoInside.Revit.GH/Components/TransactionBaseComponent.cs
@@ -263,7 +263,7 @@ protected static bool SolveOptionalLevels(ARDB.Document doc, Rhino.Geometry.Curv
     #region Geometry Conversion
     public static bool TryGetCurveAtPlane(Curve curve, Plane plane, out ARDB.Curve projected)
     {
-      if (Curve.ProjectToPlane(curve, plane) is Curve p)
+      if (curve.ProjectToPlane(plane) is Curve p)
       {
         var tol = GeometryTolerance.Model;
 
diff --git a/src/RhinoInside.Revit.GH/Components/Views/CropRegion.cs b/src/RhinoInside.Revit.GH/Components/Views/CropRegion.cs
index caa6b2048..4e6c5bbb9 100644
--- a/src/RhinoInside.Revit.GH/Components/Views/CropRegion.cs
+++ b/src/RhinoInside.Revit.GH/Components/Views/CropRegion.cs
@@ -129,7 +129,7 @@ protected override void TrySolveInstance(IGH_DataAccess DA)
         if (Params.GetData(DA, "Crop Region", out Curve cropRegion))
         {
           var viewLocation = view.Location;
-          var curveLoop = Curve.ProjectToPlane(cropRegion, viewLocation)?.ToCurveLoop();
+          var curveLoop = cropRegion.ProjectToPlane(viewLocation)?.ToCurveLoop();
           if (curveLoop is null || !cropManager.IsCropRegionShapeValid(curveLoop))
           {
             AddRuntimeMessage
diff --git a/src/RhinoInside.Revit.GH/Types/HostObjects/CurtainCell.cs b/src/RhinoInside.Revit.GH/Types/HostObjects/CurtainCell.cs
index d85eabc27..b4f5ea716 100644
--- a/src/RhinoInside.Revit.GH/Types/HostObjects/CurtainCell.cs
+++ b/src/RhinoInside.Revit.GH/Types/HostObjects/CurtainCell.cs
@@ -159,7 +159,7 @@ public Surface Surface
           var curves = new List<Curve>();
           foreach (var loop in planarCurves)
           {
-            var curve = Curve.ProjectToPlane(loop, plane);
+            var curve = loop.ProjectToPlane(plane);
             bbox.Union(curve.GetBoundingBox(plane));
             curves.Add(curve);
           }
diff --git a/src/RhinoInside.Revit.GH/Types/Sketch.cs b/src/RhinoInside.Revit.GH/Types/Sketch.cs
index 34c9662e0..dc30a36b9 100644
--- a/src/RhinoInside.Revit.GH/Types/Sketch.cs
+++ b/src/RhinoInside.Revit.GH/Types/Sketch.cs
@@ -223,7 +223,7 @@ void RemoveConstraints()
       var pi = 0;
       foreach (var boundary in boundaries)
       {
-        var profile = Curve.ProjectToPlane(boundary, plane);
+        var profile = boundary.ProjectToPlane(plane);
 
         if
         (
diff --git a/src/RhinoInside.Revit.GH/Types/Topology/SpatialElement.cs b/src/RhinoInside.Revit.GH/Types/Topology/SpatialElement.cs
index 93f77b5e4..ed4064a59 100755
--- a/src/RhinoInside.Revit.GH/Types/Topology/SpatialElement.cs
+++ b/src/RhinoInside.Revit.GH/Types/Topology/SpatialElement.cs
@@ -64,7 +64,7 @@ public Curve[] Boundaries
               var segments = spatial.GetBoundarySegments(options);
               _Boundaries = segments.Select
               (
-                loop => Curve.JoinCurves(loop.Select(x => Curve.ProjectToPlane(x.GetCurve().ToCurve(), plane)), tol.VertexTolerance, preserveDirection: false)[0]
+                loop => Curve.JoinCurves(loop.Select(x => x.GetCurve().ToCurve().ProjectToPlane(plane)), tol.VertexTolerance, preserveDirection: false)[0]
               ).ToArray();
             }
           }