topic Re: Get NurbsSurface from BRepFace in Fusion API and Scripts Forum

Get NurbsSurface from BRepFace

Anonymous — Wed, 29 Mar 2017 17:33:58 GMT

How can I get a NurbsSurface from a BRepFace?

Thanks,

Re: Get NurbsSurface from BRepFace

ekinsb — Wed, 29 Mar 2017 17:59:27 GMT

A face can have several different types of underlying surface geometry. For example it can be a plane, cylinder, sphere, etc. The geometry property of the BRepFace object will return the associated surface geometry. Non analytical shapes are represented by NURBS surfaces. However, because the analytical shapes can also be accurately represented by NURBS surfaces it's possible to always get a NURBS surface from a face. To get a NURBS surface you can use the convert method of the BRepFace object. This doesn't change the model but returns the equivalent geometry but as a NURBS surface.

Re: Get NurbsSurface from BRepFace

Anonymous — Wed, 29 Mar 2017 18:11:33 GMT

Great, thanks for the info.

The Fusion 360 API Help states that I get a BRepBody back from a call to BRepFace->convert() (C++).

I'm trying to get various (NURBS) properties from the face like degreeU, degreeV, controlPointsCountU, controlPointsCountV, all of which are associated with a NurbsSurface.

So, how can I these NURBS properties from a BRepFace?

Ptr bRepBodies = rootComponent->bRepBodies();

Ptr bRepBody = bRepBodies->item(0); // Just get the first one in this example

Ptr bRepFace = bRepBody->item(0); // Just get the first one in this example

--- Code to convert the BRepFace info to a NurbsSurface ---

Ptr nurbsSurface = ???

orderU = nurbsSurface->degreeU();

orderV = nurbsSurface->degreeV();

numCtrlPtsU = nurbsSurface->controlPointCountU();

numCtrlPtsV = nurbsSurface->controlPointCountV();

Re: Get NurbsSurface from BRepFace

ekinsb — Wed, 29 Mar 2017 18:18:35 GMT

You use the geometry property of the BRepFace object. For example if you have a box and get the geometry property from one of the BRepFace objects of the box it will return a Plane object. But if you use the Convert to get a new BRepFace, the geometry property on the new face will return a NurbsSurface object, which you can then use to get the information you're looking for.

Re: Get NurbsSurface from BRepFace

Anonymous — Wed, 29 Mar 2017 18:38:36 GMT

So I tried the following code:

BRepConvertOptions bRepConvertOptions = BRepConvertOptions( ProceduralToNURBSConversion |

AnalyticsToNURBSConversion |

PlanesToNURBSConversion |

SplitPeriodicFacesConversion );

Ptr<BRepFace> bRepFace = face->convert( bRepConvertOptions );

nurbsSurface = bRepFace->geometry();

and the bRepFace pointer is null.

In this code segment I know that “face” is a BRepFace which is one of the faces of a cube.

Am I missing a few steps?

Re: Get NurbsSurface from BRepFace

Anonymous — Wed, 29 Mar 2017 18:45:11 GMT

I think I got it:

BRepConvertOptions bRepConvertOptions = BRepConvertOptions( ProceduralToNURBSConversion |

AnalyticsToNURBSConversion |

PlanesToNURBSConversion |

SplitPeriodicFacesConversion );

Ptr<BRepBody> bRepBody = face->convert( bRepConvertOptions );

Ptr<BRepFace> bRepFace = bRepBody->faces()->item(0);

nurbsSurface = bRepFace->geometry();

I was missing pulling the BRepFace from the collection of the converted BRepBody.

Now I get all of the information that I need.

Thanks again for all of your help.

Re: Get NurbsSurface from BRepFace

ekinsb — Wed, 29 Mar 2017 20:12:12 GMT

Glad you got it working. Using convert on a BRepFace object can sometimes return more than one face because there are cases where the face will be split during the conversion. That's the reason that the convert method returns a BRepBody and not a BRepFace.