topic Re: Programmatically Getting a Polyline of intersection of Loft and a plane in .NET Forum

Programmatically Getting a Polyline of intersection of Loft and a plane

ekoneo — Thu, 23 Jun 2022 21:48:33 GMT

Hi,

How can I get a polyline that is an intersection of a plane and loft object programmatically in c#? Plane can be any object. In fact I need a cross sectional polyline object.

I try to figure with a image. There is a rectangular plane and a loft object. I need this intersection polyline as shown:

Thanks.

Re: Programmatically Getting a Polyline of intersection of Loft and a plane

R.Gerritsen4967 — Fri, 24 Jun 2022 07:15:35 GMT

Have a look here. (especially @SEANT61's post)

It's not perfect, but it will get you started.

I have used this piece of code before, but in the case of your drawing it will, unfortunately, give you only a part of the intersection.

Re: Programmatically Getting a Polyline of intersection of Loft and a plane

_gile — Fri, 24 Jun 2022 08:40:44 GMT

Hi,

If the "loft object" is a Solid3d, you could use the Solid3d.GetSection() method.

But according to your screencast, it seems to be a Surface. In this case, you could use the Surface.SliceByPlane() method on a temporary clone of the "loft object" and use the Brep API to retrieve the edges of the concerned face (this is not that trivial).

Re: Programmatically Getting a Polyline of intersection of Loft and a plane

R.Gerritsen4967 — Fri, 24 Jun 2022 09:20:36 GMT

@_gile,

I see there is also a Surface.SliceBySurface method. This seems to be a bit more versatile if you also want to get sections with non-planar surfaces.

Do you perhaps know how to convert the SurfaceSliceResults (result of SliceBy... method) to a curve?

Or do you make a new surface with SurfaceSliceResults.NewSurface and then extract the edges?

Re: Programmatically Getting a Polyline of intersection of Loft and a plane

_gile — Fri, 24 Jun 2022 10:05:57 GMT

As far as I know there's no way to directly convert a Surface (as returned by SurfaceSliceResults.NegativeHalfSurface or SurfaceSliceResults.NewSurface) into a curve. You have to extract the edges of one of the slice resulting surfaces.

Re: Programmatically Getting a Polyline of intersection of Loft and a plane

_gile — Fri, 24 Jun 2022 16:33:13 GMT

Here's an example slicing the selected Surface with an horizontal plane at specified elevation.

using Autodesk.AutoCAD.ApplicationServices; using Autodesk.AutoCAD.BoundaryRepresentation; using Autodesk.AutoCAD.DatabaseServices; using Autodesk.AutoCAD.EditorInput; using Autodesk.AutoCAD.Geometry; using Autodesk.AutoCAD.Runtime; using System.Linq; using static System.Math; namespace SelectViewportSample { using AcDb = Autodesk.AutoCAD.DatabaseServices; using AcRx = Autodesk.AutoCAD.Runtime; public class Commands { [CommandMethod("TEST")] public static void Test() { var doc = Application.DocumentManager.MdiActiveDocument; var db = doc.Database; var ed = doc.Editor; var peo = new PromptEntityOptions("\nSelect Surface: "); peo.SetRejectMessage("\nSelected object is not a Surface."); peo.AddAllowedClass(typeof(AcDb.Surface), false); var per = ed.GetEntity(peo); if (per.Status != PromptStatus.OK) return; var pdr = ed.GetDouble("\nEnter the plane elevation: "); if (pdr.Status != PromptStatus.OK) return; double elevation = pdr.Value; using (var tr = db.TransactionManager.StartTransaction()) { var surface = (AcDb.Surface)tr.GetObject(per.ObjectId, OpenMode.ForWrite); var plane = new Plane(new Point3d(0.0, 0.0, elevation), Vector3d.ZAxis); try { var sliceResults = surface.SliceByPlane(plane); using (var negativeHalfResult = sliceResults.NegativeHalfSurface) using (sliceResults.NewSurface) using (var brep = new Brep(sliceResults.NegativeHalfSurface)) { var curSpace = (BlockTableRecord)tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite); var edges = brep.Edges .Where(e => Abs(e.Vertex1.Point.Z - elevation) < 1e-12 && Abs(e.Vertex2.Point.Z - elevation) < 1e-12) .Select(e => Curve.CreateFromGeCurve(((ExternalCurve3d)e.Curve).NativeCurve)); foreach (var edge in edges) { edge.ColorIndex = 1; curSpace.AppendEntity(edge); tr.AddNewlyCreatedDBObject(edge, true); } } tr.Commit(); } catch (AcRx.Exception ex) when (ex.ErrorStatus == AcRx.ErrorStatus.NoIntersections) { ed.WriteMessage("\nThe Plane does not slice the Surface."); } catch (System.Exception ex) { ed.WriteMessage($"\n{ex.Message}"); } } } } }

Re: Programmatically Getting a Polyline of intersection of Loft and a plane

ekoneo — Fri, 24 Jun 2022 18:57:14 GMT

Hi @_gile and @R.Gerritsen4967 ,

Thanks for your help and interest. Thank you for helping for this kind of difficult problem for me. I try your advices.

Re: Programmatically Getting a Polyline of intersection of Loft and a plane

ekoneo — Fri, 24 Jun 2022 22:12:30 GMT

@_gile I try your sample. It works perfectly. Result is 4 piece of splines that are on the intersection plane an the surface. My thanks are less than your helps.

Ynt: Programmatically Getting a Polyline of intersection of Loft and a plane

ekoneo — Tue, 28 Jun 2022 12:09:01 GMT

Hi @_gile,

Depending on loft surface shape, the result intersection objects can be more than 1 objects as spline, polyline, circle etc.

I try to join if there are more than 1 pieces.

Green, Red, Yellow and Magenta colored splines

int count = 0; foreach (var edge in edges) { edge.ColorIndex = 1; curSpace.AppendEntity(edge); tr.AddNewlyCreatedDBObject(edge, true); if (count == 0) { obj = edge; } else if (count == 1) { obj.JoinEntity(edge); count++; } } tr.AddNewlyCreatedDBObject(obj, true);

Unfortunatelly, I couldn't get success result. How can I join result objects?

Thanks again.

Ynt: Programmatically Getting a Polyline of intersection of Loft and a plane

_gile — Tue, 28 Jun 2022 15:44:16 GMT

As far as I know, you cannot join splines.

The only way to get a single entity is to create a Region from the resulting curves with Region.CreateFromCurves method.

Ynt: Programmatically Getting a Polyline of intersection of Loft and a plane

ekoneo — Tue, 28 Jun 2022 15:53:49 GMT

Thanks.. Is it possible to use "DistanceTo" function with region? I need distance between Cogo point and the polyline, spline or region.

On the other hand, after your code produced splines, I can manually join them.

Thanks @_gile

Ynt: Programmatically Getting a Polyline of intersection of Loft and a plane

_gile — Tue, 28 Jun 2022 16:51:44 GMT

You can generate a polyline which approximate the spline with the Spline.ToPolyline method if you accept to loose a little accuracy.

Ynt: Programmatically Getting a Polyline of intersection of Loft and a plane

ekoneo — Tue, 28 Jun 2022 19:32:50 GMT

Thank you @_gile. I try your advice.