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How to Create a B-Spline Surface

Question asked by Tim Fromme on Jul 6, 2017
Latest reply on Jul 7, 2017 by Peter Brinkhuis

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Hello,

I have all the data necessary to create B-Spline Surfaces, however the API is not very clear to me with them. There is CreateBSplineSurface, ICreateBSplineSurface, and ICreateBSplineSurfaceDLL which all seem to do the same thing. I have tried a lot of different combinations of formatting the input to these functions, but I always seem to get an object variable not set error or a type mismatch error. The first two functions ask for objects as input, and the last function asks for a long and three doubles, but the documentation and required input suggests that they should be arrays of some kind. I have coding experience, but have not used VBA in forever.

UPDATE:

I have since figured out why I was getting errors, it had to do with not instantiating the body as a new body in a part. I am getting no more errors, however I crash solidworks every time that I try to run the macro, on the function call for CreateBSplineSurface or ICreateBSplineSurface.

UPDATE2:

I have been able to get this method working in C#, with separate issues that I feel are different enough to merit opening a different discussion on.

How to trim a closed surface?

Thanks in advance.

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Peter Brinkhuis Jul 6, 2017 2:41 PM

Can you share your code?

You could prevent crashes by adding lines like the following:

On Error GoTo LabelX

code that can cause an error

LabelX:

Label you jump to when an error occurs.

We might be able to prevent the error from happening altogether though

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Tim Fromme @ Peter Brinkhuis on Jul 6, 2017 3:02 PM

Here is the relevant code:

Sub main()

Dim swApp As Object

Set swApp = Application.SldWorks

Dim swModel As SldWorks.IModelDoc2

Set swModel = swApp.ActiveDoc

Dim swPart As SldWorks.IPartDoc

Set swPart = swModel

Dim body As IBody2

Set body = swPart.ICreateNewBody2

Dim Props(7) As Integer

Dim UKnots(5) As Double

Dim VKnots(5) As Double

Dim CtrlPtCoords(26) As Double

Props(0) = 3

...

Props(7) = 0

UKnots(0) = 0#

...

UKnots(5) = 1#

VKnots(0) = 0#

...

VKnots(5) = 1#

CtrlPtCoords(0) = 0#

...

CtrlPtCoords(26) = 0#

Dim surface As ISurface

Set surface = body.ICreateBsplineSurface(Props, UKnots, VKnots, CtrlPtCoords) LINE CAUSING ERROR

body.CreateBodyFromSurfaces

End Sub

The error is happening on pretty much the most important line in the program, and always gives an Access Violation Error.

Crash occurs on SW16 and 17 when there is a part open, without a part open there is a different error relating to the activeDoc line, which makes sense.

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Peter Brinkhuis @ Tim Fromme on Jul 6, 2017 4:42 PM

You could start by changing IPart to Part etc for all objects, otherwise you are apparently defining interfaces instead of objects.

You might also need some checks to make sure that "body" is not nothing. If it is, you shouldn't perform any actions on it. The same holds for parts, you can check the type before setting swPart equal to swModel.

Regarding the parameters, they can be messy sometimes. Certainly when the help says something like "These are integers packed into a double array", while it is supposed to be an object. An example would really help there, because I also don't know exactly what to feed this function. I might try creating an array and copying it to an object before passing it as a parameter.

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Tim Fromme @ Peter Brinkhuis on Jul 6, 2017 5:51 PM

After changing the interfaces to objects and doing some checks, it looks like the issue is in how I am passing the data to the function. Will look at more next week. :/

Side note: I only really need to get raw nurb data into solidworks, I don't care how I do it. Saving to IGES and 3DM didn't work as well as I would have hoped, but if anyone has suggestions in general for this, that would be greatly appreciated.

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Peter Brinkhuis @ Tim Fromme on Jul 7, 2017 6:05 AM

I tried the same. It just crashes on the troubled line, even my error handling doesn't catch it. It would have been nice if they would make a function a little more robust when it is so hard to create a set of proper parameters.

I have no idea how to create a set of parameters that should work. There are a few forum questions about this function, but no real answers. I haven't worked with either splines or surfaces, so that makes it harder I also couldn't find a button to create such a surface in the GUI, so it's unclear to me what it should do exactly. If there is a button available, maybe we can record an example.

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5 Replies

Peter Brinkhuis Jul 6, 2017 2:41 PM
Mark Correct
Correct Answer
Can you share your code?

You could prevent crashes by adding lines like the following:

On Error GoTo LabelX
code that can cause an error
LabelX:
Label you jump to when an error occurs.

We might be able to prevent the error from happening altogether though
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- Tim Fromme @ Peter Brinkhuis on Jul 6, 2017 3:02 PM
  Mark Correct
  Correct Answer
  Here is the relevant code:
  Sub main()
  Dim swApp As Object
  Set swApp = Application.SldWorks
  Dim swModel As SldWorks.IModelDoc2
  Set swModel = swApp.ActiveDoc
  Dim swPart As SldWorks.IPartDoc
  Set swPart = swModel
  
  Dim body As IBody2
  Set body = swPart.ICreateNewBody2
  
  Dim Props(7) As Integer
  Dim UKnots(5) As Double
  Dim VKnots(5) As Double
  Dim CtrlPtCoords(26) As Double
  
  Props(0) = 3
  ...
  Props(7) = 0
  
  UKnots(0) = 0#
  ...
  UKnots(5) = 1#
  
  VKnots(0) = 0#
  ...
  VKnots(5) = 1#
  
  CtrlPtCoords(0) = 0#
  ...
  CtrlPtCoords(26) = 0#
  
  Dim surface As ISurface
  Set surface = body.ICreateBsplineSurface(Props, UKnots, VKnots, CtrlPtCoords) LINE CAUSING ERROR
  body.CreateBodyFromSurfaces
  
  End Sub
  
  The error is happening on pretty much the most important line in the program, and always gives an Access Violation Error.
  Crash occurs on SW16 and 17 when there is a part open, without a part open there is a different error relating to the activeDoc line, which makes sense.
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  - Peter Brinkhuis @ Tim Fromme on Jul 6, 2017 4:42 PM
    Mark Correct
    Correct Answer
    You could start by changing IPart to Part etc for all objects, otherwise you are apparently defining interfaces instead of objects.
    
    You might also need some checks to make sure that "body" is not nothing. If it is, you shouldn't perform any actions on it. The same holds for parts, you can check the type before setting swPart equal to swModel.
    
    Regarding the parameters, they can be messy sometimes. Certainly when the help says something like "These are integers packed into a double array", while it is supposed to be an object. An example would really help there, because I also don't know exactly what to feed this function. I might try creating an array and copying it to an object before passing it as a parameter.
    Like • Show 0 Likes0
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    - Tim Fromme @ Peter Brinkhuis on Jul 6, 2017 5:51 PM
      Mark Correct
      Correct Answer
      After changing the interfaces to objects and doing some checks, it looks like the issue is in how I am passing the data to the function. Will look at more next week. :/
      Side note: I only really need to get raw nurb data into solidworks, I don't care how I do it. Saving to IGES and 3DM didn't work as well as I would have hoped, but if anyone has suggestions in general for this, that would be greatly appreciated.
      Like • Show 0 Likes0
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      - Peter Brinkhuis @ Tim Fromme on Jul 7, 2017 6:05 AM
        Mark Correct
        Correct Answer
        I tried the same. It just crashes on the troubled line, even my error handling doesn't catch it. It would have been nice if they would make a function a little more robust when it is so hard to create a set of proper parameters.
        
        I have no idea how to create a set of parameters that should work. There are a few forum questions about this function, but no real answers. I haven't worked with either splines or surfaces, so that makes it harder I also couldn't find a button to create such a surface in the GUI, so it's unclear to me what it should do exactly. If there is a button available, maybe we can record an example.
        Like • Show 0 Likes0
        Actions

How to Create a B-Spline Surface

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