Intersection Point Between Spline and Surface determined by line in XY plane

[a_kloczewiak]

Hi everyone. Is it possible in C# to find the intersection point of a spline with a surface in AutoCAD? The surface should be determined based on line in the x,y plane. Thanks in advance for any suggestions.

[Y.AUBRY]

Hi @a_kloczewiak,

Try to use curve entity instead of spline and look at this post as an exemple : 

Dim acCurve As Curve = TryCast(tr.GetObject(per.ObjectId, OpenMode.ForRead), Curve)

https://www.keanw.com/2015/09/intersecting-autocad-curves-with-a-plane-using-net.html

Imports Autodesk.AutoCAD.ApplicationServices
Imports Autodesk.AutoCAD.DatabaseServices
Imports Autodesk.AutoCAD.EditorInput
Imports Autodesk.AutoCAD.Geometry
Imports Autodesk.AutoCAD.Runtime
Imports System
Imports System.Runtime.CompilerServices

Namespace EntityIntersections
    Module Extensions
        <Extension()>
        Function ToArray(ByVal pts As Point3dCollection) As Point3d()
            Dim res = New Point3d(pts.Count - 1) {}
            pts.CopyTo(res, 0)
            Return res
        End Function

        <Extension()>
        Function IntersectWith(ByVal p As Plane, ByVal cur As Curve) As Point3d()
            Dim pts = New Point3dCollection()
            Dim gcur = cur.GetGeCurve()
            Dim proj = TryCast(gcur.GetProjectedEntity(p, p.Normal), Curve3d)

            If proj IsNot Nothing Then

                Using gcur2 = Curve.CreateFromGeCurve(proj)
                    cur.IntersectWith(gcur2, Intersect.OnBothOperands, pts, IntPtr.Zero, IntPtr.Zero)
                End Using
            End If

            Return pts.ToArray()
        End Function

        <Extension()>
        Function IsOn(ByVal cv As Curve, ByVal pt As Point3d) As Boolean
            Try
                Dim p = cv.GetClosestPointTo(pt, False)
                Return (p - pt).Length <= Tolerance.[Global].EqualPoint
            Catch
            End Try

            Return False
        End Function
    End Module

    Public Class Commands
        <CommandMethod("CPI")>
        Public Sub CurvePlaneIntersection()
            Dim doc = Application.DocumentManager.MdiActiveDocument
            If doc Is Nothing Then Return
            Dim db = doc.Database
            Dim ed = doc.Editor
            Dim peo = New PromptEntityOptions(vbLf & "Select a curve")
            peo.SetRejectMessage("Must be a curve.")
            peo.AddAllowedClass(GetType(Curve), False)
            Dim per = ed.GetEntity(peo)
            If per.Status <> PromptStatus.OK Then Return
            Dim curId = per.ObjectId
            Dim peo2 = New PromptEntityOptions(vbLf & "Select plane surface")
            peo.SetRejectMessage("Must be a planar surface.")
            peo.AddAllowedClass(GetType(PlaneSurface), False)
            Dim per2 = ed.GetEntity(peo2)
            If per2.Status <> PromptStatus.OK Then Return
            Dim planeId = per2.ObjectId

            Using tr = doc.TransactionManager.StartTransaction()
                Dim plane = TryCast(tr.GetObject(planeId, OpenMode.ForRead), PlaneSurface)

                If plane IsNot Nothing Then
                    Dim p = plane.GetPlane()
                    Dim cur = TryCast(tr.GetObject(curId, OpenMode.ForRead), Curve)

                    If cur IsNot Nothing Then
                        Dim pts = p.IntersectWith(cur)
                        Dim ms = CType(tr.GetObject(SymbolUtilityServices.GetBlockModelSpaceId(db), OpenMode.ForWrite), BlockTableRecord)

                        For Each pt As Point3d In pts
                            Dim dbp = New DBPoint(pt)
                            dbp.ColorIndex = 2
                            ms.AppendEntity(dbp)
                            tr.AddNewlyCreatedDBObject(dbp, True)
                            ed.WriteMessage(vbLf & "Point is {0} curve.", If(cur.IsOn(pt), "on", "off"))
                        Next
                    End If
                End If

                tr.Commit()
            End Using
        End Sub
    End Class
End Namespace

[_gile]

Hi,

Try this way:

[CommandMethod("FindIntersection")]
public void FindIntersectionMethod()
{
    var doc = Application.DocumentManager.MdiActiveDocument;
    var db = doc.Database;
    var ed = doc.Editor;

    var peo = new PromptEntityOptions("\nSelect a line in the XY plane: ");
    peo.SetRejectMessage("\nSelected object must be a line.");
    peo.AddAllowedClass(typeof(Line), true);
    var per = ed.GetEntity(peo);
    if (per.Status != PromptStatus.OK)
        return;

    using (var tr = db.TransactionManager.StartTransaction())
    {
        var line = (Line)tr.GetObject(per.ObjectId, OpenMode.ForRead);
        var direction = line.StartPoint.GetVectorTo(line.EndPoint);
        if (direction.Z != 0.0)
        {
            ed.WriteMessage("\nSelected line is not parallel to XY plane.");
            return;
        }

        peo.Message = "\nSelect a 3D spline: ";
        peo.RemoveAllowedClass(typeof(Line));
        peo.SetRejectMessage("\nSelected object must be a spline.");
        peo.AddAllowedClass(typeof(Spline), true);
        per = ed.GetEntity(peo);
        if (per.Status != PromptStatus.OK)
            return;
        var spline = (Spline)tr.GetObject(per.ObjectId, OpenMode.ForRead);

        var plane = new Plane(line.StartPoint, new Vector3d(-direction.Y, direction.X, 0.0));

        var points = new Point3dCollection();
        using (var projectedCurve = spline.GetOrthoProjectedCurve(plane))
        {
            spline.IntersectWith(projectedCurve, Intersect.OnBothOperands, points, IntPtr.Zero, IntPtr.Zero);
        }

        if (points.Count > 0)
        {
            foreach (Point3d point in points)
            {
                ed.WriteMessage($"\nIntersection point: X={point.X}, Y={point.Y}, Z={point.Z}");
            }
        }
        else
        {
            ed.WriteMessage("\nNo intersection point found.");
        }

        tr.Commit();
    }
}