Tue, 09/24/2013 - 21:41
Forums:
Hi guys,
using OpenCASCADE6.6.0 we run into a problem while converting a mesh. The following code results in the exception
"Unhandled exception at 0x00481b62 in OCCSample.exe: 0xC0000005: Access violation reading location 0xfefd0000."
void OCCConverter::ConvertToCurve(const TopoDS_Edge& _edge)
{
Standard_Real first, last;
BRep_Tool::Range(_edge,first,last);
Handle_Geom_Curve geomCurve = BRep_Tool::Curve(_edge, first, last);
if(geomCurve!=NULL)
{
Handle_Standard_Type type = geomCurve->DynamicType();
std::cerr DynamicType()->Name()
}
...
However, most often this succeeds:
processing type Compound
Geom_BSplineCurve
...
Geom_BSplineCurve
*exception occurs*
Do you have an idea about what I am doing wrong?
Thank you very much in advance.
Tue, 09/24/2013 - 21:59
Hello,
It could be a number of thing. Usually it means that at one point you got a NULL point. From your source code it could be _edge, geomCurve or geomCurve->DynamicType().
Best way to solve this is to go step by step using the debugger.
Good luck,
Francois.
Tue, 09/24/2013 - 22:11
Hi François,
thank you very much for the answer.
_edge is a const TopoDS_Edge&, cannot be NULL.
geomCurve is checked for not being NULL.
geomCurve->DynamicType() throws the exception.
Stepping through this with the debugger only jumps to
myfile.cpp:geomCurve->DynamicType();
handle_geom_curve.hxx:DEFINE_STANDARD_HANDLE(Geom_Curve,Geom_Geometry)
handle_standard_transient.hxx: Standard_Transient* ControlAccess() const { return entity; }
handle_geom_curve.hxx:DEFINE_STANDARD_HANDLE(Geom_Curve,Geom_Geometry)
myfile.cpp:geomCurve->DynamicType();
*exception occurs*
So what may this be?
Tue, 09/24/2013 - 23:17
Hi David,
First off:
> _edge is a const TopoDS_Edge&, cannot be NULL.
This is not true, is you test _edge.IsNull() is could be NULL, even if you have a const TopoDS_Edge& because TopoDS_Edge is derived from TopoDS_Shape and TopoDS_Shape hold a reference to a pointer, a location and an orientation.
Also, I usually test for NULL pointer using the IsNull() method in OCC, never use the !=NULL so I'm not sure it is working that way. Try expanding the variable geomCurve in the debugger up until you see the entity variable from Handle_Standard_Transient to see if you could find a valid pointer value there.
So you could test for _edge.IsNull() and if it is good, check for geomCurve.IsNull().
Francois.
Wed, 09/25/2013 - 15:03
Hi François,
thank you for solving my problem. I wasnt aware of the IsNull() function and the reference inside the data structures.
The code
Handle_Geom_Curve geomCurve = BRep_Tool::Curve(_edge, first, last);
seems to return a null handle. The documentation for BRep_Tool::Curve says: "Returns the 3D curve of the edge. May be a Null handle", but not when a null handle is the result of the operation. I wonder how this can happen.
Wed, 09/25/2013 - 17:10
Hi David,
have a look at the manual modata.pdf, it is all explained there in details.
And for the _edge case, if the _edge is not NULL, this means you have at least a 3d curve or a 2d curve (curve on surface) or both. So in your case, if geomCurve is NULL you probably only have a 2d curve (use BRep_Tool::CurveOnSurface to retrieve it).
If you really need a 3d curve and only have a 2d curve, you could use ShapeFix_Edge::FixAddCurve3d, this will build a 3d curve for you based on your 2d curve.
Francois.
Wed, 09/25/2013 - 18:40
Hi François,
i wasnt aware that the really useable documentation comes with the non-document executable. Thank you for all your valuable tips.
Cheers,
David