Contours on BSPSurface

Thanks a lot Guido !

I better understand (I think) the way to set the boundaries. I "just" have to implement that now :).

The tessellation process is more explicit too : I identified the BRepMesh_IncrementalMesh class but I had no idea how to parse the triangles.

I will  try that on monday now, have a nice WE.

Marc

Hi,

The code is working pretty well ! Thanks a lot it has been fast to develop with your example. I used it (modifying it a bit) to manage various kind of surfaces & boundaries.

But ... :) ... using the process to cut planes is OK but when I try to do that with BSP surfaces, the tessellation is not working any more.

You can find below 3 parts of simplified code :

- one to generate the wire of a closed boundary (TopoDS_Wire)

- one to generate the BRep surface (topoDS_Face) adding the boundaries

- one to tessellate the BRep surface

Handle(TopTools_HSequenceOfShape) Edges = new TopTools_HSequenceOfShape();
        
    for(unsigned int i = 0; i < curves.size(); i++)
    {
            Handle(Geom_Curve) c = curves[i];
                        
            // Project the curve on the surface ?
            //Handle(Geom_Curve) c2 = GeomProjLib::Project(c,p_surf);

            BRepBuilderAPI_MakeEdge me(c, c->FirstParameter(),c->LastParameter());
            BRepLib::BuildCurve3d(me.Edge());
            Edges->Append(me.Edge());
        }
    }
    
    // weld the edges to have only 1 wire for the boundary

    Handle(TopTools_HSequenceOfShape) Wires = new TopTools_HSequenceOfShape();
    // Connect all the edges to create a single wire
    ShapeAnalysis_FreeBounds::ConnectEdgesToWires(Edges, WELD_TOLERANCE, false, Wires); 
    

    Handle(TopTools_HSequenceOfShape) ClosedWires = new TopTools_HSequenceOfShape();
    Handle(TopTools_HSequenceOfShape) OpenWires = new TopTools_HSequenceOfShape();
    ShapeAnalysis_FreeBounds::SplitWires(Wires,WELD_TOLERANCE,false,ClosedWires,OpenWires);
    Standard_Integer nbWires = ClosedWires->Length();
    
    if(nbWires>1) 
    {
        printf("Error : too much wires for the current boundary\n");
    }
    else if( nbWires==0)
    {
        printf("Error : no wire for the current boundary\n");
        return false;
    }

    TopoDS_Wire w= TopoDS::Wire(ClosedWires->Value(1));

     BRepBuilderAPI_MakeFace mf(m_surf,outerBoundary); // outerBoundaries[i] is a TopoDS_Wire 

    for(unsigned int i = 1; i < innerBoundaries.size(); i++)
    {
            mf.Add( innerBoundaries[i] ); // innerBoundaries[i] is a TopoDS_Wire 
    }
    
    TopoDS_Face f = mf;

     BRepMesh_IncrementalMesh im(f,0.2);

    im.Perform();

    TopLoc_Location faceLocation;

    Handle(Poly_Triangulation)   tri = BRep_Tool::Triangulation(f, faceLocation);

As you can see I did not project the curves (which are all "Geom_Curve") on my surface (I store all the surfaces as "Geom_Surface") before creating the wire for the boundary. I tried to do it but without success.

I was wondering if this is the reason why the tessellation fails (the surface is created, the wires for the boundaries seems to be OK too but the result of triangulation is NULL). Have you got any idea to solve this issue ? By the way, without boundaries the tessellation is working.

I won't be able to send you code before next wednesday :'( ... I will try to write you a full (but simple) example of what I'd like to do on wednesday. Thanks again for the help.

EDIT : It seems I do not understand well the process to create the boundaries on surfaces from Geom_Curve objects. I tried to project the curves on the surface to create the boundaries but it was not really efficient. To summarize : I have an object (Geom_Surface) & some boundaries (Geom_Curves) and I would like to cut the surface with the boundaries (I have uploaded a drawing to illustrate the process I would like to achieve). I have implemented the process following your advises :

- get the surface & boundaries and store them

- convert each boundary as a wire (*)

              - using BRepBuilderAPI_MakeEdge to get edges from each curve of the boundary

              -  ShapeAnalysis_FreeBounds::ConnectEdgesToWires to create a single wire (and ShapeAnalysis_FreeBounds::SplitWires to get the first closed wire)

- create a Face using BRepBuilderAPI_MakeFace and add each boundary as wire (with the Add method)

- then I tessellate the face using BRepMesh_IncrementalMesh & BRep_Tool::Triangulation

(*) I tried to use BOPTools_AlgoTools2D::MakePCurveOnFace to project the Geom_curve as Geom2d_curve (inspired by the following post :  https://www.opencascade.com/content/topodsedge-built-geom2dcurve-and-geomsurface-has-not-pcurve-face but It is not working on planes any more :), and it gives a result on BSP surfaces but not the one I waited for; when I "mesh" it, only the boundaries are used to create the triangles, it seems to not take into account the BSplineSurface).

It is quite difficult to get a source code from my project since it is developed to be quite generic and create the surfaces/curves from files (surfaces & curves creation checked displaying them in the open cascade MFC sample app Geometry). I will try to create an example in a single file and post it there asap.

Do you think I am on the right way to apply boundaries on any kind of surfaces to tessellate them or should I rewrite the full process ?

re - EDIT ! Eventually, it seems that tessellation is working with other surfaces than planes when projection is done ... I did set the angle degeneration too high in BRepMesh_IncrementalMesh !

Eventually I identified one of the surface I import which raises an exception in the program. I wrote a code to set it as raw data and do the process I would like to achieve. You may be able to see better where is my mistake (because I must be doing one but no way to have a clue on that !).

The code should generate a tessellated "Arc" of cylinder as final result (if using the triangles & nodes arrays).

You can find the full source code below. The exception is raised while trying to call BuildCurve3D (for the first curve, the first segment):

#include "Geom_CylindricalSurface.hxx"
#include "TopoDS_Edge.hxx"
#include "TopoDS_Wire.hxx"
#include "gp_Ax2.hxx"
#include "gp_Ax3.hxx"
#include "BRep_Builder.hxx"
#include "BOPTools_AlgoTools2D.hxx"
#include "BRepBuilderAPI_MakeEdge.hxx"
#include "GC_MakeSegment.hxx"
#include "gp_Elips.hxx"
#include "GC_MakeArcOfEllipse.hxx"
#include "BRepLib.hxx"
#include "ShapeAnalysis_FreeBounds.hxx"
#include "BRepBuilderAPI_MakeFace.hxx"
#include "TopoDS.hxx"
#include "BRepMesh_IncrementalMesh.hxx"


int main(int argc, char ** argv)
{

	gp_Pnt cent(141.920000, 3.679000, 0.268000);

	gp_Dir norm(1.000000, 0.000000, 0.000000);

	gp_Vec mAxis(0.000000, -0.012000, 0.000000);

	double r = mAxis.Magnitude();

	gp_Dir xAxis(mAxis);

	gp_Ax3 axis(cent,norm,xAxis);

	Handle(Geom_Surface) surf = new Geom_CylindricalSurface(axis,r);





	BRep_Builder aBuilder;

	TopoDS_Face f;

	aBuilder.MakeFace(f, surf, Precision::Confusion() );





	std::vector<Handle(Geom_Curve)> outerBoundary;



	gp_Pnt b1(141.920000,3.691000,0.268000);

	gp_Pnt e1(156.980000,3.691000,0.268000);

	GC_MakeSegment mkSeg(b1,e1);

	outerBoundary.push_back(mkSeg.Value());





	gp_Pnt el1Center(156.980000, 3.679000, 0.268000);

	gp_Dir el1Norm(-1.000000, 0.000000, 0.000000);

	gp_Vec el1MAxis(0.000000, -0.012000, 0.000000);

	gp_Dir el1xAxis(el1MAxis);

	gp_Ax2 el1Axis(el1Center, el1Norm, el1xAxis);

	double radius = el1MAxis.Magnitude();

	gp_Elips el1(el1Axis,radius, radius);

	GC_MakeArcOfEllipse aoe1(el1,3.141593,4.188790,Standard_True);

	outerBoundary.push_back(aoe1.Value());





	gp_Pnt b2(156.980000,3.685000,0.257608);

	gp_Pnt e2(141.920000,3.685000,0.257608);

	GC_MakeSegment mkSeg2(b2,e2);

	outerBoundary.push_back(mkSeg2.Value());





	gp_Pnt el2Center(141.920000, 3.679000, 0.268000);

	gp_Dir el2Norm(1.000000, 0.000000, 0.000000);

	gp_Vec el2MAxis(0.000000, -0.012000, 0.000000);

	gp_Dir el2xAxis(el2MAxis);

	gp_Ax2 el2Axis(el2Center, el2Norm, el2xAxis);

	double radius2 = el2MAxis.Magnitude();

	gp_Elips el2(el2Axis,radius2, radius2);

	GC_MakeArcOfEllipse aoe2(el2,2.094395,3.141593,Standard_True);

	outerBoundary.push_back(aoe2.Value());





	Handle(TopTools_HSequenceOfShape) Edges = new TopTools_HSequenceOfShape();

	std::vector<Handle(Geom_Curve)>::iterator it = outerBoundary.begin();

	for(;it!=outerBoundary.end(); it++)

	{

		Handle(Geom_Curve) c = *it;

		Handle(Geom2d_Curve) c2 = NULL;

		Standard_Real tol = 1.0;

		BOPTools_AlgoTools2D::MakePCurveOnFace(f, c, c->FirstParameter(), c->LastParameter(), c2,tol);

		// build the edges from the Geom2D_Curve (result of the projection of the 3D curve on the surface)

		BRepBuilderAPI_MakeEdge me(c2, surf);

		TopoDS_Edge e = me.Edge();

		BRepLib::BuildCurve3d(e);   // Exception raised : first chance exception, access violation reading at address 0x0000000000000000 (but I cannot find the null pointer in "e")

		Edges->Append(e);

	}



	Handle(TopTools_HSequenceOfShape) Wires = new TopTools_HSequenceOfShape();

	// Connect all the edges to create a single wire

	ShapeAnalysis_FreeBounds::ConnectEdgesToWires(Edges, 0.0001, false, Wires); // if shared = true , the connection is done only if the vertices are the same





	BRepBuilderAPI_MakeFace mf(surf, TopoDS::Wire(Wires->Value(1)) );

	for(int k = 1; k < Wires->Length(); k++)

		mf.Add( TopoDS::Wire(Wires->Value(k+1)) );   // should not be called since only 1 wire may be generated



	TopoDS_Face face2Tessellate = mf.Face();





	BRepMesh_IncrementalMesh im(face2Tessellate,0.1, true ,0.1 ,false, false);

	im.Perform();

	TopLoc_Location faceLocation; // faceLocation will not be used 

	Handle(Poly_Triangulation) tri;

	tri = BRep_Tool::Triangulation(f, faceLocation);

	if(!tri.IsNull())

	{

		Poly_Array1OfTriangle triangles = tri->Triangles();

		TColgp_Array1OfPnt nodes = tri->Nodes();

	}

	return 0;
}

Hi Guido,

You can find an example of the surface which does not work well with the process I developed in one of my previous post. I replaced BOPTools_AlgoTools2D::MakePCurveOnFace by BRep_Tool::CurveOnSurface, but then the resulting 2D curve is null. All the curves I use are defined so they are already described to be on the surface (but I still need to project them to process BRepBuilderAPI_MakeFace) since they are from another BRep description (but not using the same surface description as OpenCascade does). I will post you the OBJ export so you can view the result if it is working for you. I think the process I developed should not be the correct one to address any kind of surfaces (when you look at it what do you think about the way I project on surface & create the boundaries/triangulation ?).

NB : As most of my cylinder surfaces are described with simple boundary (arc of ellipse, segment following the axis of the cylinder, arc of ellipse , segment following the cylinder axis), I just created a GeomFill::Surface between the 2 arcs of ellipse. But this is more a trick than a solution. This enables me to get more surfaces but not all of them.

Best regards

Marc

Hi,

Back on this issue ! I isolated a simple case : projection of a circle on a cylinder. 

I just cannot understand why I cannot project an ellipse on a cylindrical surface ? I tried to but the Geom2d_Curve returned is always empty (null).

The little section of code I used to test that is the following one : I create a cylindrical surface and an ellipse with exactly the same parameters (axis, radius, center).

	gp_Pnt center(0.0, 0.0, 0.0);
	gp_Dir normal(0.0, 0.0, 1.0);
	gp_Dir xAxis(1.0, 0.0, 0.0 );
	gp_Ax3 axis(center, normal, xAxis);
	double r = 1.0;


	Handle(Geom_Surface) surf = new Geom_CylindricalSurface(axis, r);
	BRepBuilderAPI_MakeFace mf(surf, Precision::Confusion());
	TopoDS_Face f = mf.Face();

	gp_Elips el1(axis, r, r);
	GC_MakeArcOfEllipse aoe1(el1, 0.0, 2 * M_PI,Standard_True);
	Handle(Geom_Curve) bottom = aoe1.Value();
	BRepBuilderAPI_MakeEdge eBottom(bottom);
	double first = bottom->FirstParameter();
	double last = bottom->LastParameter();
	Handle(Geom2d_Curve) bottom2D = BRep_Tool::CurveOnSurface(eBottom.Edge(), f, first, last);

But the ellipse projection fails : bottom2D is always null ! :( "Something is rotten in the state of Denmark" :). Seriously, may I use another method to project any curve on my cylinder (projection of segments on cylinder is null too), or should I create the cylinder surface another way ?

I hope someone could help me ( Guido :) ? )