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IDProjectCategoryView StatusDate SubmittedLast Update
0033900CommunityOCCT:Modeling Algorithmspublic2025-08-12 15:332026-01-07 15:05
Reporterj.bourgoin Assigned Toj.bourgoin  
PrioritynormalSeveritymajor 
Status feedbackResolutionopen 
PlatformWindowsOSVC++ 2022 
Product Version7.7.1 
Summary0033900: Bad STEP import
DescriptionHello,

The attached file is well seen on some CAD softwares, but import it with OCC gives a flat surface instead on a volume with 20 um of thickness.

Steps To ReproduceThis code allows to scale the shape and see clearly the (bad) result :
        STEPControl_Reader reader ;
        reader.ReadFile("C:\\CU.STEP") ;
        reader.TransferRoots() ;
        TopoDS_Shape shape = reader.OneShape() ;

        // Scale
        gp_GTrsf gtrsf ;
        gtrsf.SetValue(1, 1, 1000.0) ;
        gtrsf.SetValue(2, 2, 1.0) ;
        gtrsf.SetValue(3, 3, 1.0) ;

        BRepBuilderAPI_GTransform gtr(shape, gtrsf, true) ;
        TopoDS_Shape scaledShape = gtr.Shape() ;

        // Save
        STEPControl_Writer writer ;
        writer.Transfer(scaledShape, STEPControl_AsIs) ;
        writer.Write("C:\\CU_scaled.STEP") ;
TagsNo tags attached.
Test case number

Attached Files

Relationships

related to 0033908 feedbackj.bourgoin Bad result with BRepAlgoAPI_Cut 

Activities

j.bourgoin

2025-08-12 15:33

reporter  

CU.STEP (99,142 bytes)   
soft2.png (42,977 bytes)   

ika

2025-09-04 18:13

reporter   ~0117078

Last edited: 2025-09-04 18:21

 Dear j.bourgoin,

I have investigated this issue, and the summary is that the OCCT's behavior is completely valid on this input data.
I also checked some other viewers (ODA Viewer and Autodesk online), and they also don't show any volume.

Here is the explanation of the file's invalidity (sorry, I deleted all the "#" from the citations from the file; otherwise, they were interpreted as another mantis issues and made the text unreadable):
The shape consists of one solid, which consists of one shell, and the shell consists of two faces:
274 = MANIFOLD_SOLID_BREP ( 'Importée1', 735 );
735 = CLOSED_SHELL ( 'NONE', ( 797, 161 ) ) ;
797 = ADVANCED_FACE ( 'NONE', ( 423, 846, 428, 786, 82, 635, 645 ), 152, .T. ) ;
161 = ADVANCED_FACE ( 'NONE', ( 613, 195, 107, 337, 479, 902, 125 ), 827, .F. ) ;

These faces are lying on the two parallel planes with a 0.2mm distance between them.
152 = PLANE ( 'NONE',  826 ) ;
827 = PLANE ( 'NONE',  706 ) ;

The problem is that there are no "walls" between these two "top" and "bottom" faces. Our STEP reader cannot imagine them, and in the attempt to fix the obviously invalid solid, it "merges" both faces into one with a tolerance value of 0.2. I will not say that such a solid is a good shape, but there is no possibility to read it "normally" with the given input data.

Issue History

Date Modified Username Field Change
2025-08-12 15:33 j.bourgoin New Issue
2025-08-12 15:33 j.bourgoin Assigned To => akaftasev
2025-08-12 15:33 j.bourgoin File Added: CU.STEP
2025-08-12 15:33 j.bourgoin File Added: soft2.png
2025-09-04 18:13 ika Note Added: 0117078
2025-09-04 18:16 ika Note Edited: 0117078
2025-09-04 18:18 ika Note Edited: 0117078
2025-09-04 18:21 ika Note Edited: 0117078
2025-10-23 11:26 dpasukhi Relationship added related to 0033908
2025-12-19 13:42 dpasukhi Note View State: 0117078: public
2026-01-07 15:05 dpasukhi Assigned To akaftasev => j.bourgoin
2026-01-07 15:05 dpasukhi Status new => feedback