topic Re: Getting 'normal vector' of non-planar surface in .NET Forum

Getting 'normal vector' of non-planar surface

R.Gerritsen4967 — Thu, 29 Oct 2020 14:11:46 GMT

I'm trying to indicate the direction for a thicken operation on a surface by drawing temporary vectors in the editor.

For planar surfaces I can use:

surface.getplane.normal

But (obviously) this does not work on non-planar surfaces.

Is there a way to determine the direction for the thickening operation?

Re: Getting 'normal vector' of non-planar surface

Alexander.Rivilis — Thu, 29 Oct 2020 15:37:09 GMT

Every point on surface has owned 'normal vector'. Maybe this article help you: https://adndevblog.typepad.com/autocad/2012/07/retrieving-a-solid3d-face-normal-through-brep-api.html

Re: Getting 'normal vector' of non-planar surface

R.Gerritsen4967 — Thu, 29 Oct 2020 16:08:14 GMT

Thanks Alexander, I'll look into it.

Do you know a way to access the surface with the brep api?

Re: Getting 'normal vector' of non-planar surface

Alexander.Rivilis — Thu, 29 Oct 2020 17:29:10 GMT

As far as I remember BREP API can work with Surface: https://adndevblog.typepad.com/autocad/2012/08/retrieving-native-curve-geometry-using-brep-api.html

Re: Getting 'normal vector' of non-planar surface

Alexander.Rivilis — Thu, 29 Oct 2020 17:34:06 GMT

Other way is creating Solid3d from Surface with method Solid3d.CreateFrom(...)

Re: Getting 'normal vector' of non-planar surface

R.Gerritsen4967 — Fri, 30 Oct 2020 11:31:26 GMT

Unfortunately this gives me an error.

However I've made some progression with the other links you provided.

Instead of Solid3d.CreateFrom(...), i now use a temporary solid made with thicken from the surface. (because a surface does not seem to have a face)

Then I use a face (the original surface) of the temp solid to determine a normal vector of the edges.

But as far as I can see, all the edges have different normal vectors.

Only points on the surface(not on the edges) have a usable normal vector. but this normal vector is not always the real normal vector unfortunately...

My code is a real mess now, so I'll do some cleaning up and try to find a working solution.

I have also tried to access the curve geometry of the edges of the surface (your 2nd link). But those curves don't seem to have anything like a 'normal' property.

Re: Getting 'normal vector' of non-planar surface

Alexander.Rivilis — Fri, 30 Oct 2020 11:39:05 GMT

@R.Gerritsen4967 wrote:

I have also tried to access the curve geometry of the edges of the surface (your 2nd link). But those curves don't seem to have anything like a 'normal' property.

Second link is only to see that it is possible to get Brep from Surface directly.

Re: Getting 'normal vector' of non-planar surface

R.Gerritsen4967 — Fri, 30 Oct 2020 12:03:05 GMT

@Alexander.Rivilis wrote:
Brep from Surface directly.

Ok. Thanks. I guess I misunderstood...;)

I think I have now solved the problem.

In a part of my code I was breaking down a surface into nurbs (according to https://through-the-interface.typepad.com/through_the_interface/2011/02/gathering-points-defining-3d-autocad-geometry-using-net.html ) to access points across the surface.

I just found out that nurbs have a normal property which I can use directly.

So now I'm able to draw temp vectors in the direction of the surface 'normal'.

Re: Getting 'normal vector' of non-planar surface

R.Gerritsen4967 — Fri, 30 Oct 2020 12:58:11 GMT

OK, I cleaned up my code a bit.

Here is a function to draw temp vectors in the normal direction of a surface:

<CommandMethod("THICKEN3D", CommandFlags.Modal)> Public Shared Sub THICKEN3D() Dim doc As Document = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument Dim ed As Editor = doc.Editor Dim db As Database = doc.Database Dim peo As New PromptEntityOptions(vbLf & "Select surface:") peo.SetRejectMessage(vbLf & "Needs to be a SURFACE!") peo.AddAllowedClass(GetType(Autodesk.AutoCAD.DatabaseServices.Surface), True) peo.AddAllowedClass(GetType(Autodesk.AutoCAD.DatabaseServices.PlaneSurface), True) peo.AddAllowedClass(GetType(Autodesk.AutoCAD.DatabaseServices.ExtrudedSurface), True) peo.AddAllowedClass(GetType(Autodesk.AutoCAD.DatabaseServices.SweptSurface), True) peo.AddAllowedClass(GetType(Autodesk.AutoCAD.DatabaseServices.LoftedSurface), True) peo.AddAllowedClass(GetType(Autodesk.AutoCAD.DatabaseServices.RevolvedSurface), True) peo.AddAllowedClass(GetType(Autodesk.AutoCAD.DatabaseServices.NurbSurface), True) Dim per As PromptEntityResult = ed.GetEntity(peo) If per.Status <> PromptStatus.OK Then Return Using trx As Transaction = db.TransactionManager.StartTransaction() Dim btr As BlockTableRecord = TryCast(trx.GetObject(db.CurrentSpaceId, OpenMode.ForWrite), BlockTableRecord) Dim ent As Entity = TryCast(trx.GetObject(per.ObjectId, OpenMode.ForWrite), Entity) Dim solPlate As New Solid3d With { .RecordHistory = True } Dim Thickness As Double = Nothing If TypeOf ent Is Autodesk.AutoCAD.DatabaseServices.Surface Then Try Dim srf As Autodesk.AutoCAD.DatabaseServices.Surface = TryCast(trx.GetObject(per.ObjectId, OpenMode.ForWrite), Autodesk.AutoCAD.DatabaseServices.Surface) ExtrusionVectors(srf) Thickness = SelDbl("Thickness: ") If Thickness = Nothing Then Exit Sub solPlate = srf.Thicken(Thickness, False) btr.AppendEntity(solPlate) trx.AddNewlyCreatedDBObject(solPlate, True) Catch ModelingFailure As Autodesk.AutoCAD.Runtime.Exception When ModelingFailure.Message = "eGeneralModelingFailure" ed.WriteMessage(vbLf & "Probably a self-intersecting surface...") trx.Abort() Return End Try End If ent.Erase() trx.Commit() End Using End Sub Public Shared Sub ExtrusionVectors(srf As Autodesk.AutoCAD.DatabaseServices.Surface) 'https://through-the-interface.typepad.com/through_the_interface/2011/02/gathering-points-defining-3d-autocad-geometry-using-net.html Dim ed As Editor = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Editor Dim vec_size As Double = Autodesk.AutoCAD.ApplicationServices.Application.GetSystemVariable("VIEWSIZE") / 10 Dim cross_size As Double = vec_size / 10 Dim nurbs As Autodesk.AutoCAD.DatabaseServices.NurbSurface() = srf.ConvertToNurbSurface For Each nurb As Autodesk.AutoCAD.DatabaseServices.NurbSurface In nurbs Dim ustart As Double = nurb.UKnots.StartParameter, uend As Double = nurb.UKnots.EndParameter, uinc As Double = 2 * (uend - ustart) / nurb.UKnots.Count, vstart As Double = nurb.VKnots.StartParameter, vend As Double = nurb.VKnots.EndParameter, vinc As Double = 2 * (vend - vstart) / nurb.VKnots.Count Dim u As Double = ustart While u <= uend Dim v As Double = vstart While v <= vend Dim vec As Vector3d = nurb.GetNormal(u, v) * vec_size If Not vec = Nothing Then Dim pt2 As Point3d = nurb.Evaluate(u, v).TransformBy(Matrix3d.Displacement(vec)) ed.DrawVector(nurb.Evaluate(u, v), pt2, 6, True) ed.DrawVector(New Point3d(pt2.X - cross_size, pt2.Y - cross_size, pt2.Z), New Point3d(pt2.X + cross_size, pt2.Y + cross_size, pt2.Z), 6, False) ed.DrawVector(New Point3d(pt2.X - cross_size, pt2.Y + cross_size, pt2.Z), New Point3d(pt2.X + cross_size, pt2.Y - cross_size, pt2.Z), 6, False) End If v += vinc End While u += uinc End While Next End Sub