Cant create Brep intersection

Rhino Developer
,
1

Hello, I try to use the CreateFromBox method and I cant get breps by doing that. This is part my code:

 Dim bbox = brep.GetBoundingBox(True)
 Dim corner = bbox.GetCorners()

For i = dt To corner(4).Z Step dt
            For j = 0 To 3 Step 1

       cor(j) = corner(j).Z + dt1
  Dim bb As New Rhino.Geometry.BoundingBox(corner(0).X, corner(0).Y, corner(0).Z, corner(j).X, corner(j).Y, cor(j))
  Dim b As New Geometry.Box(bb)                                                     
  Dim bbrep = Geometry.Brep.CreateFromBox(b)
  RhinoApp.WriteLine(bbrep.ToString)
  Dim inters As Brep() = Brep.CreateBooleanIntersection(brep, bbrep, 1)

 Next
            dt1 = dt1 + dt
        Next

I get this error: “Value cannot be null.” from Dim inters As Brep() = Brep.CreateBooleanIntersection(brep, bbrep, 1). And RhinoApp.WriteLine(bbrep.ToString) give me “Object reference not set to an instance of an object.”

Can someone tell me how to solve this problem please?
Thanks.

2

Basic debugging involves testing if you get what you expect after creating new things. See the text "' < Test for null/Nothing > which I injected here and there in your code.

Try that first and ask more if you don’t see where things goes wrong.

Dim bbox = brep.GetBoundingBox(True)
'  < Test for null/Nothing >
Dim corner = bbox.GetCorners()
'  < Test for null/Nothing >

For i = dt To corner(4).Z Step dt
    For j = 0 To 3 Step 1
        cor(j) = corner(j).Z + dt1
        Dim bb As New Rhino.Geometry.BoundingBox(corner(0).X, corner(0).Y, corner(0).Z, corner(j).X, corner(j).Y, cor(j))
        '  < Test for null/Nothing >
        Dim b As New Geometry.Box(bb)
        '  < Test for null/Nothing >
        Dim bbrep = Geometry.Brep.CreateFromBox(b)
        '  < Test for null/Nothing >
        RhinoApp.WriteLine(bbrep.ToString)
        '  < Test for null/Nothing >
        Dim inters As Brep() = Brep.CreateBooleanIntersection(brep, bbrep, 1)   
        '  < Test for null/Nothing >
    Next
    dt1 = dt1 + dt
Next

// Rolf

3

Yes, I tested it a lot of times. Everything before Dim bbrep = Geometry.Brep.CreateFromBox(b) is fine.

4

Is the b BoundingBox valid ?

http://developer.rhino3d.com/api/RhinoCommonWin/html/P_Rhino_Geometry_BoundingBox_IsValid.htm

5

The tests should be in your code. There are no test in your code.

// Rolf

6

Dim bb As New Rhino.Geometry.BoundingBox(corner(0).X, corner(0).Y, corner(0).Z, corner(j).X, corner(j).Y, cor(j))
If Not bb.IsValid Then
RhinoApp.WriteLine(“INVALID bb”)
Return Rhino.Commands.Result.Failure

            End If
            Dim b As New Geometry.Box(bb)
            If Not b.IsValid Then
                RhinoApp.WriteLine("INVALID b")
                Return Rhino.Commands.Result.Failure

            End If
            Dim bbrep = Geometry.Brep.CreateFromBox(b)
            If bbrep Is Nothing Then
                RhinoApp.WriteLine("INVALID bbrep")
                Return Rhino.Commands.Result.Failure

            End If

The result: “INVALID bbrep”

7

Then check the values you used in the constructor and see if something is not what you expect

8

Your debugging skills are improving. :wink:

Try also this before trying to create the bbrep

  if (bbox.IsDegenerate(doc.ModelAbsoluteTolerance) > 0) {
    RhinoApp.WriteLine("the curve's bounding box is degenerate (flat) in at least one direction so a box cannot be created.");

See this page:
http://developer.rhino3d.com/5/api/RhinoCommonWin/html/M_Rhino_Geometry_Brep_CreateFromBox.htm

// Rolf

9

The box is not degenerate

10

Have you done what Rolf told you ?

You might find that the box is really degenerate …

If I read your code correctly, the first iteration of the loop seems to build a box using the same vertex twice and simply changing the second Z … ( but obviously I may be wrong :confused: )

You can easily verify that by printing the values before passing them to the constructor … no ? :slight_smile:

11

Yes…That was the mistake, plus the second loop…
I think this is correct:
Dim bb As New Rhino.Geometry.BoundingBox(corner(0).X, corner(0).Y, corner(0).Z, corner(2).X, corner(2).Y, cor(j))

Thanks a lot guys