When I run the command given in the code below on just a simple Plane surface, the splitting the plane’s only BrepFace (let’s call it I) once results in a Brep with two faces. Let’s call them A and B.

Split(I) => [A|B]

When I subsequently split face A again, let’s call the two halves of this splitting A1 and A2. The result, however, is a Brep with three faces: A1, A2 and B. I think that the split operation on A should not include face B.

Split(A) => [A1|A2|B] This is what I find

Split(A) => [A1|A2] This is what I expect

Brepface Split Results.3dm (48.9 KB)

```
protected override Result RunCommand(RhinoDoc doc, RunMode mode)
{
ObjRef srfRef;
Result res = RhinoGet.GetOneObject("Select surface to split", false, ObjectType.Surface, out srfRef);
if (res != Result.Success) return res;
BrepFace bf = srfRef.Surface() as BrepFace;
if (null == bf)
return Result.Failure;
bool atV = false;
res = RhinoGet.GetBool("Split at U or V isocurve?", true, "U", "V", ref atV);
if (res != Result.Success) return res;
Split( new[] {bf}, atV, doc);
doc.Views.Redraw();
return Result.Success;
}
private Result Split(BrepFace[] faces, bool atV, RhinoDoc doc)
{
foreach (var bf in faces)
{
GetPoint splitAtPoint = new GetPoint();
splitAtPoint.Constrain(bf, false);
splitAtPoint.DynamicDraw += (o, a) =>
{
double u, v;
if (bf.ClosestPoint(a.CurrentPoint, out u, out v))
{
Curve iso = bf.IsoCurve(atV ? 0 : 1, atV ? v : u);
a.Display.DrawCurve(iso, Color.LightGray);
}
};
GetResult res = splitAtPoint.Get();
if (res == GetResult.Point)
{
double u, v;
if (bf.ClosestPoint(splitAtPoint.Point(), out u, out v))
{
Curve[] iso = bf.TrimAwareIsoCurve(atV ? 0 : 1, atV ? v : u);
if (iso.Length == 1)
{
Brep split = bf.Split(iso, doc.ModelAbsoluteTolerance);
if (split.Faces.Count > 2)
{
doc.Objects.Add(bf.DuplicateFace(false), new ObjectAttributes {Name = "input"});
doc.Objects.Add(split, new ObjectAttributes {Name = "result with >2 faces!"});
return Result.Failure;
}
doc.Objects.Add(split, new ObjectAttributes {Name = "split with <= 2 faces!"});
Split(split.Faces.ToArray(), atV, doc);
}
}
}
if (res == GetResult.Cancel)
return Result.Cancel;
}
return Result.Success;
}
```