Can we inspect the surface being merged by two faces in OpenCASCADE?

Hello Author,

Could you please explain what exactly you mean by "the direction of sample point"?
Do you mean the normal direction at points, or you mean direction between two neighbor points, or anything else?

Thanks in advance,
Commenter-1

the direction of sample point is similar to direction between two neighbor points. I used a parametric formula (U = t * a + b) to sample point in the parametric patch of surface. t is the direction vector.

In Attach File,I write my sample direction in it,you can see the green is different the purple.

It should be same as the purple points.
Due to this result,I guess that surface is merged.

Ok Author,

It's understood now. Your assumption is likely correct (though you do not provide your IGES file) - usually CAD models are composed of several patches (faces) that can be based on absolutely different surfaces, with absolutely different parametrization. To inspect such models (let's call them shell-based), you need to write specialized algorithms to build the trajectories correctly.

If you like to know how we can help you, please, contact us at http://www.opencascade.com/contact.
Best regards,
Commenter-1