Fuse method does not work for edges - Forum Open Cascade Technology

Martin Melbourne
Wed, 04/12/2017 - 17:37

Forums:

Hello, I think i have an understanding issue here, but when i try to fuse to two edges together like this, the result still has two edges.

Do i use the fuse algorithm in a wrong way, or do i have to do something else?

pt1 = OCC.gp.gp_Pnt(0,0,0)
pt2 = OCC.gp.gp_Pnt(3,0,0)
pt3 = OCC.gp.gp_Pnt(1,0,0)
pt4 = OCC.gp.gp_Pnt(5,0,0)

edge1 = OCC.BRepBuilderAPI.BRepBuilderAPI_MakeEdge(pt1,pt2).Edge()
edge2 = OCC.BRepBuilderAPI.BRepBuilderAPI_MakeEdge(pt3,pt4).Edge()

fuse = OCC.BRepAlgoAPI.BRepAlgoAPI_Fuse(edge1, edge2).Shape()

edges = []
exp = OCC.TopExp.TopExp_Explorer(fuse, OCC.TopAbs.TopAbs_EDGE)
while exp.More():
    edge = OCC.TopoDS.topods.Edge(exp.Current())
    edges.append(edge)
    exp.Next()
return edges

results in two edges, I need one.

unif = OCC.ShapeUpgrade.ShapeUpgrade_UnifySameDomain(fuse)
unif.Build()
unif.UnifyEdges()

even results in three edges :)

Any help is appreciated!

Cheers.

Martin Melbourne
Thu, 04/13/2017 - 10:46

Okay, I solved it using:

BRepLib_FuseEdges(BRepAlgoAPI_Fuse(edge1, edge2).Shape())

though i don't yet understand why the normal boolean fuse does not just unify the two edges.

*edit

apparently

TopOpeBRepTool_FuseEdges

does the same, are there any differences, or advantages to using one of the methods, or is there a better one? Basically I need do fuse edges that can be fuse (i.e. I would check for common and unify them if common has been found, to get one edge)

**edit

BRepAlgoAPI_Fuse(edge1, edge2) only fuses the edges into one edge if they have exactly the same coordinates

Forum supervisor
Thu, 04/13/2017 - 11:05

Dear Martin,

As you can see from Draw script below, an operation of merging 2 your edges properly produces a shape with 3 edges, what can be joined to a wire and unified to a shape with 1 edge.

vertex v1 0 0 0 vertex v2 3 0 0 vertex v3 1 0 0 vertex v4 5 0 0

edge e1 v1 v2 edge e2 v3 v4

bfuse r e1 e2

nbs r

# EDGE : 3

eval wire w [explode r e]

unifysamedom result w

don result

nbs result

# EDGE : 1

Best regards,

Forum supervisor

Martin Melbourne
Thu, 04/13/2017 - 11:18

Thanks for your help, can you explaine to me what the other two methods (BRepLib_FuseEdges and TopOpeBRepTool_FuseEdges) do, and where they differ from your solution?

Martin Melbourne
Thu, 04/13/2017 - 11:31

Your Solution does not seem to work for me :/

pt1 = OCC.gp.gp_Pnt(0,0,0)
pt2 = OCC.gp.gp_Pnt(3,0,0)
pt3 = OCC.gp.gp_Pnt(1,0,0)
pt4 = OCC.gp.gp_Pnt(3,0,0)

edge1 = OCC.BRepBuilderAPI.BRepBuilderAPI_MakeEdge(pt1,pt2).Edge()
edge2 = OCC.BRepBuilderAPI.BRepBuilderAPI_MakeEdge(pt3,pt4).Edge()

wire = OCC.BRepBuilderAPI.BRepBuilderAPI_MakeWire()
wire.Add(edge1)
wire.Add(edge2)
wire.Wire()

unif = OCC.ShapeUpgrade.ShapeUpgrade_UnifySameDomain(wire.Shape())
unif.Build()
unif.UnifyEdges()

get_edges(unif.Shape())

The result are still 2 edges

Eugeny
Fri, 04/21/2017 - 14:10

This solution does not work because you've missed the step in which the edges are fused (bfuse r e1 e2). The unification algorithm works only on topologically shared objects, i.e. the edges should be connected.

Martin Melbourne
Thu, 04/13/2017 - 14:45