How to get wires from single face? - Forum Open Cascade Technology

Malcolm Revenge
Mon, 08/14/2017 - 02:53

Forums:

Hi! I need collection of 3d lines of shape edges, how i can get it?

I have TopoDS_Shape, i know, how to iterate all faces, so i have TopoDS_Face -s, and now i want to take edges of each face for rendering it with custom 3d engine. I need simple collection of 3d lines, like this: LINE1(v1,v2), LINE2(v1,v2) and so on...

need help :(

Malcolm Revenge
Mon, 08/14/2017 - 11:00

Guys, ok. I don't need edges of single face :-) I need all edges of the shape,for example, box have 10 edges. How i can to retrieve this edges of my shape?

qa qa
Mon, 08/14/2017 - 11:23

Hello,

Please look at "TopExp_Explorer" class. It allows to iterate over sub-shapes.

qa qa

Malcolm Revenge
Mon, 08/14/2017 - 11:40

Please look at "TopExp_Explorer" class. It allows to iterate over sub-shapes.

Thank you very much for reply! But sorry, i'm really newbie in OCC, can you show me few lines of C++ code to get edges of...for example, simple box shape? I need collection of 3d lines with start and end vertices for each line to drawing native in OpenGl as lines...

P.S.: at now i really don't understand, how OCC topology works, handlers...strange class names, strange FOR itarators...:-)

Thanks

Jeason Diesel
Mon, 08/14/2017 - 11:47

Hello！ You can search "TopExp_Explorer" in your OCC samples (just like "Geometry" or "Modeling" which is in "All-vc-10").And you can solve many problems in this way !Just try "ctrl+F"

Attachments:

93GXZTJOGGEGVMRNPW.png

qa qa
Mon, 08/14/2017 - 11:50

Hello,

Here is my short sample:

  TopoDS_Shape aShape = ...; // Your initial shape.
  for (TopExp_Explorer anExp(aShape, TopAbs_EDGE); anExp.More(); anExp.Next())
  {
    // Iterate over edges in input shape.
    const TopoDS_Edge& anEdge = TopoDS::Edge(anExp.Current());

    // Take geometrical data from edge.
    Standard_Real aF, aL;
    Handle(Geom_Curve) aCurve = BRep_Tool::Curve(anEdge, aF, aL);

    // After that, it is possible to take sample points to discretize the curve.
    const Standard_Integer NBPOINTS = 10;
    for (Standard_Integer i = 1; i <= NBPOINTS; ++i)
    {
      Standard_Real aPreviousPntParam = aF + (aL - aF) * (i - 1) / (NBPOINTS);
      Standard_Real aCurrentPntParam =  aF + (aL - aF) *  i      / (NBPOINTS);

      gp_Pnt aPreviousPnt = aCurve->Value(aPreviousPntParam);
      gp_Pnt aCurrentPnt = aCurve->Value(aCurrentPntParam);

      // aPreviousPnt, aCurrentPnt - points on which you can construct line.
    }
  }

qa qa

Malcolm Revenge
Mon, 08/14/2017 - 12:20

Here is my short sample:

Thank you! you are my idol! :-)

Hmm.. If my edges is a simple segments (simple box shape), it's mean, that here i need only 2 points? Can i iterate over segment edges or in any case, i need first iterate over curves and after transform it into the line segment?

qa qa
Mon, 08/14/2017 - 12:48

Well, when your underlying curves are represented by lines, this snippet can be significantly simplified - you can you use TopExp::Vertices(...) instead of discretization procedure. Here is updated sample:

  TopoDS_Shape aShape = ...; // Your initial shape.
  for (TopExp_Explorer anExp(aShape, TopAbs_EDGE); anExp.More(); anExp.Next())
  {
    // Iterate over edges in input shape.
    const TopoDS_Edge& anEdge = TopoDS::Edge(anExp.Current());

    // Take the first and the last vertices from edge
    TopoDS_Vertex aVFirst = TopExp::FirstVertex(anEdge);
    TopoDS_Vertex aVLast  = TopExp::LastVertex(anEdge);

    // Take geometrical information from vertices.
    gp_Pnt aPntFirst = BRep_Tool::Pnt(aVFirst);
    gp_Pnt aPntLast = BRep_Tool::Pnt(aVLast);
  }

qa qa

Malcolm Revenge
Mon, 08/14/2017 - 14:28

Wow! Many thanks, bro!