Getting geometric points from TopoDS_Edge - Forum Open Cascade Technology

Sam Shrum
Mon, 11/11/2013 - 21:42

Forums:

Is there a way to get the geometric points from a curved TopoDS_Edge? I know I can use TopExp_Explorer to get the endpoints, but I want to get the geometric coordinates of a series of intermediate points by a certain tolerance.

Arjan Schouten
Tue, 11/12/2013 - 22:57

Hello Sam,

CheckOut GCPnts_UniformAbscissa

BRepAdaptor_Curve curveAdaptor;
curveAdaptor.Initialize(yourEdge);

GCPnts_UniformAbscissa uniformAbscissa;
uniformAbscissa.Initialize(curveAdaptor, yourTolerance);

if(uniformAbscissa.IsDone())
{
}

Sam Shrum
Thu, 11/14/2013 - 02:17

Hi Arjan,

I think I'm missing something. Are there any initializers which take only the curve adaptor and the tolerance? It looks like they all require either a NbPoints value or Abscissa value; I don't know ahead of time how many points I want (I need them within a physical tolerance, however many that requires), nor do I understand what the Abscissa value would be.

However if I understand correctly, could I then get the points out via something like this?

Standard_Real parameter = uniformAbscissa.Parameter(i);
gp_Pnt p = curveAdaptor.Value(parameter);

Thanks!

Arjan Schouten
Thu, 11/14/2013 - 18:34

Hi Sam,

My mistake, I confused tolerance with abscissa.

If you use it like,

GCPnts_UniformAbscissa uniformAbscissa;
uniformAbscissa.Initialize(curveAdaptor, 5.0);

it will generate points evenly spaced at 5mm along your edge.

You then loop through the number of generated points.

Kind Regards,

Arjan

Sam Shrum
Fri, 11/15/2013 - 03:29

Hi Arjan,

That makes sense, but what's the call to get each point out? The function "Parameter" returns a double/Standard_Real, but I don't really understand what it's in terms of- is it a U or V parameter I can use to get a point? Is there a function I'm missing that returns a geometric point?

Thanks!