VB.net: Perpendicular lines to a polyline

[Jozi68]

I use vb.net. I work in 2D.
I have a certain point (Point3D). I have a certain polyline. I need to draw a perpendicular line from the point to the polyline. Any ideas on how to do that??

[SEANT]

This is typically done with Curve.GetClosestPointTo(). The point returned from that method can be combined with the input point to create a line.

[Jozi68]

Thanx Seant,
Can you please show me how to implement this statement? I have no idea how.

[SEANT]

There may be a detail or two overlooked in this sample, but it shows the general idea.

   Public Sub Per2Poly()
        Dim db As Database = HostApplicationServices.WorkingDatabase
        Dim ed As Editor = Application.DocumentManager.MdiActiveDocument.Editor
        db.Pdmode = 66 'just to make the points more visible
        Dim tr As Transaction = db.TransactionManager.StartTransaction()
        Dim peo As PromptEntityOptions = New PromptEntityOptions(vbCr & "Select a lwpline: ")
        peo.SetRejectMessage(vbCr & "Please select lightweight polyline only! ")
        peo.AddAllowedClass(GetType(Polyline), True)
        Try
            Dim per As PromptEntityResult = ed.GetEntity(peo)
            If per.Status <> PromptStatus.OK Then Exit Sub
            Dim mat As Matrix3d = ed.CurrentUserCoordinateSystem
            Dim pl As Polyline = tr.GetObject(per.ObjectId, OpenMode.ForRead)

            Dim ppo As PromptPointOptions = New PromptPointOptions(vbCr & "Select point from which to strike a perpendicular: " & vbLf)
            ppo.AllowNone = True

            Dim ppr As PromptPointResult = ed.GetPoint(ppo)
            If ppr.Status <> PromptStatus.OK Then Exit Sub
            Dim basePt As Point3d = ppr.Value.TransformBy(mat)
            Dim pt As Point3d = pl.GetClosestPointTo(basePt, False) 'crux of the process

            Dim v3d As Vector3d = basePt.GetVectorTo(pt)       'Test if closest point is indeed perpendicular.
            Dim derV3d As Vector3d = pl.GetFirstDerivative(pt) '
            If v3d.IsPerpendicularTo(derV3d) Then              '
                Dim ln As Line = New Line(basePt, pt)
                Dim btr As BlockTableRecord = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite)
                ln.SetDatabaseDefaults()
                btr.AppendEntity(ln)
                tr.AddNewlyCreatedDBObject(ln, True)
                tr.Commit()
            Else
                ed.WriteMessage(vbCr & "Perpendicular not found!")
            End If
        Catch ex As Exception
            tr.Abort()
            ed.WriteMessage("Error during execution! " & ex.Message)
        Finally
            tr.Dispose()
        End Try

    End Sub

[Jozi68]

Thanx SEANT,
I got it to work