Error when trying to convert an Edge to a Geom_Curve

Kreshnik
Tue, 05/17/2005 - 17:09

Forums:

Other usage issues

Hi,

I want to convert an Edge to a Geom_Curve. I try this code :

TopoDS_Edge anEdge = TopoDS::Edge(myAISContext->SelectedShape()) ;

Handle(Geom_Curve) myCurve = BRep_Tool::Curve(anEdge, First, Last);

Handle(Geom_BSplineCurve) myBSplCurve = Handle(Geom_BSplineCurve)::DownCast( myCurve);

I have the following compilation error :

C:\OpenCASCADE5.2\samples\standard\Mfc\Selection\src\AISSelectDoc.cpp(321) : error C2065: 'First' : undeclared identifier
C:\OpenCASCADE5.2\samples\standard\Mfc\Selection\src\AISSelectDoc.cpp(321) : error C2065: 'Last' : undeclared identifier

Can someone help me ?

Thanks in advance for your answer

Francois Lauzon (not verified)
Tue, 05/17/2005 - 17:22

Looks like you didn't declare First and Last,

Standard_Real First,Last;

for example...

Kreshnik
Tue, 05/17/2005 - 17:26

Merci Francois,

Je suis nouveau en OCC et VC++ alors je me perds des fois sur des petits détail.

Kreshnik
Tue, 05/31/2005 - 15:09

Hi,

What is First and Last ? What is their role ?

Thanks

ES (not verified)
Thu, 05/19/2005 - 12:03

you have to Handle(Geom_Curve) myCurve = BRep_Tool::Curve(anEdge);
to no limit edge.

Kreshnik
Tue, 05/31/2005 - 15:39

Hi,

What is First and Last ? What is their role ?

Thanks

Rob Bachrach
Tue, 05/31/2005 - 15:43

First and Last are filled in on output from the Curve function.
They contain the bounding parameters of the curve defining the edge.
So, if the edge is a circular arc, the curve is a circle and first and
last contain the parameters (angles) that trim the circle to the arc.

Kreshnik
Tue, 05/31/2005 - 15:58

Thank you Bob.

I have always then same problem : I select an edge in GUI and I want to obtain the vertices of this edge or the BSpline description.
I obtain errors !

Thanks

Rob Bachrach
Tue, 05/31/2005 - 16:06

Once you've defined First and Last as Standard_Real, does your
code then compile? What errors do you receive now?

Kreshnik
Tue, 05/31/2005 - 16:22

Thanks Rob

My code :

Handle(Geom_Curve) myCurve = BRep_Tool::Curve(myEdge, First, Last);
Handle(Geom_BSplineCurve) myBSplCurve = GeomConvert::CurveToBSplineCurve(myCurve);

There are no compilation error but when I execute this part of code I've this error : 0093C336C:Standard_DomainError:No such curve.

Thanks

Rob Bachrach
Tue, 05/31/2005 - 16:32

Look at the Exceptions documentation for GeomConvert::CurveToBSplineCurve. It states the reasons for a DomainError:

- if the curve C is infinite, or
- if C is a (complete) circle or ellipse, and Parameterisation is equal to Convert_TgtThetaOver2_1 or Convert_TgtThetaOver2_2.

Although it is possible that your problem is the later, I have a feeling your problem is the former (ie. the curve is infinite).
CurveToBSplineCurve only works on finite curves. The Curve function is probably returning an infinite curve (which is limited by First, Last). You may need to create a trimmed curve (Geom_TrimmedCurve) using the curve and parameters before converting to a BSpline.

Kreshnik
Tue, 05/31/2005 - 16:46

How can I do ? The edge than I select is the edge of a cube.

Thanks.

Rob Bachrach
Tue, 05/31/2005 - 17:02

In that case, your edge is almost certainly an infinite line trimmed by First and Last. Try:

Handle(Geom_Curve) myCurve = BRep_Tool::Curve(myEdge, First, Last);
Handle(Geom_TrimmedCurve) myTrimmed = new Geom_TrimmedCurve(myCurve, First, Last);
Handle(Geom_BSplineCurve) myBSplCurve = GeomConvert::CurveToBSplineCurve(myTrimmed);

Kreshnik
Tue, 05/31/2005 - 17:07

I works. Thank you very much Rob. People like you are very important in the developpemnt world.