Project to 2D - Forum Open Cascade Technology

Alexander Kaszynski
Thu, 12/14/2023 - 20:48

Forums:

I'd like to project a part to 2D using hidden line removal with HLRAlgo_Projector, but the projection is off and I can't figure out why. I've disabled the perspective transformation and the coordinate system is perfectly top down and it still looks like it's being projected with a perspective. Here's a code snippet (using pyOCCT), and I've attached a screenshot of the generated lines.

Please let me know what needs to be changed to render an orthographic projection of the part.

# Define the transformation for the isometric projection
direction = gp_Dir(0.0, 1, 0)
point = gp_Pnt(0, 0, 0)
coordinate_system_3d = gp_Ax3(point, direction)

# Create a transformation from the coordinate system
transformation = gp_Trsf()
transformation.SetTransformation(coordinate_system_3d)

# Create the projector with orthogonal projection
projector = HLRAlgo_Projector(transformation, False, 0.0)

hlr = HLRBRep_Algo()
hlr.Add(shape.wrapped)

hlr.Projector(projector)
hlr.Update()
hlr.Hide()

hlr_shapes = HLRBRep_HLRToShape(hlr)

Attachments:

visible.png

tmp.png

Dmitrii Pasukhin
Thu, 12/14/2023 - 21:28

Hello, please try to use gp_Ax2 instead of (gp_Trsf False 0.0). Just single gp_Ax2

Unfortunatelly, I have no more ideas.

Best regards, Dmitrii.

Alexander Kaszynski
Thu, 12/14/2023 - 23:18

Worked! Here's the part I changed:

ax2 = gp_Ax2()
ax2.SetLocation(gp_Pnt(0.0, 0.0, 0.0))
ax2.SetDirection(gp_Dir(0.0, 1.0, 0.0))
ax2.SetXDirection(gp_Dir(1.0, 0.0, 0.0))

projector = HLRAlgo_Projector(ax2)

hlr = HLRBRep_Algo()
hlr.Add(shape.wrapped)

hlr.Projector(projector)
hlr.Update()
hlr.Hide()

Thanks for your help.

Shing Liu
Fri, 12/15/2023 - 03:45

Hello, You can check the examples in the document: HLR Examples https://dev.opencascade.org/doc/overview/html/occt_user_guides__modeling_algos.html#occt_modalg_10_1

For exact HLR algorithm, you need HLRBRep_HLRToShape to extract the result.

// Build The algorithm object 
myAlgo = new HLRBRep_Algo(); 

// Add Shapes into the algorithm 
TopTools_ListIteratorOfListOfShape anIterator(myListOfShape); 
for (;anIterator.More();anIterator.Next()) 
myAlgo->Add(anIterator.Value(),myNbIsos); 

// Set The Projector (myProjector is a HLRAlgo_Projector) 
myAlgo->Projector(myProjector); 

// Build HLR 
myAlgo->Update(); 

// Set The Edge Status 
myAlgo->Hide(); 

// Build the extraction object : 
HLRBRep_HLRToShape aHLRToShape(myAlgo); 

// extract the results : 
TopoDS_Shape VCompound           = aHLRToShape.VCompound(); 
TopoDS_Shape Rg1LineVCompound                            = 
aHLRToShape.Rg1LineVCompound(); 
TopoDS_Shape RgNLineVCompound                            = 
aHLRToShape.RgNLineVCompound(); 
TopoDS_Shape OutLineVCompound                            = 
aHLRToShape.OutLineVCompound(); 
TopoDS_Shape IsoLineVCompound                            = 
aHLRToShape.IsoLineVCompound(); 
TopoDS_Shape HCompound           = aHLRToShape.HCompound(); 
TopoDS_Shape Rg1LineHCompound                            = 
aHLRToShape.Rg1LineHCompound(); 
TopoDS_Shape RgNLineHCompound                            = 
aHLRToShape.RgNLineHCompound(); 
TopoDS_Shape OutLineHCompound                            = 
aHLRToShape.OutLineHCompound(); 
TopoDS_Shape IsoLineHCompound                            = 
aHLRToShape.IsoLineHCompound();

Alexander Kaszynski
Thu, 12/14/2023 - 23:32

Follow up question: Is there any way to get the original faces associated with each extracted edge?

Dmitrii Pasukhin
Fri, 12/15/2023 - 02:52

Looking into source code i dont see the options for that.

Shing Liu
Fri, 12/15/2023 - 03:51

You can get the original edge for the extracted edge.

Alexander Kaszynski
Mon, 12/18/2023 - 19:44

Cool! Could you please let me know how to do that?

Shing Liu
Tue, 12/19/2023 - 06:05

Sorry, I misunderstand.

You can get the hidden/visible part of shape edges by give the shape to VCompound, HCompound, .etc.

TopoDS_Shape VCompound (const TopoDS_Shape& S);
TopoDS_Shape OutLineVCompound (const TopoDS_Shape& S);
TopoDS_Shape HCompound (const TopoDS_Shape& S);
TopoDS_Shape OutLineHCompound (const TopoDS_Shape& S);