Fix sibling component intersections in fused CAD exports (#939)

[joergbrech]

Description

Fixes #939.

Fused IGES/STEP/BRep exports of a full aircraft only considered CPACS parent-child relationships when fusing components. Sibling components that geometrically intersect one another but not through their shared parent (e.g. a horizontal and vertical tailplane that both attach to the fuselage and also intersect each other near the tail) were never fused against each
other. Their overlap region showed up as unfused/internal geometry in the exported solid.

An initial fix made the fusing algorithm consider all sibling components pairwise instead of only parent-child pairs, but this still fused them one pair at a time (running result + next component). That incremental approach cannot correctly resolve a genuine mutual/triple intersection between three or more components meeting in the same region (fuselage + HTP + VTP all overlapping near the tail) - it produced a self-intersecting solid with missing faces once tested against a more realistic geometry.

This PR replaces the incremental pairwise fuse with a single n-ary BRepAlgoAPI_Fuse operation over all aircraft components at once (CTiglFusePlane::Perform()), which resolves mutual intersections between any number of components consistently in one pass. A proper TopoDS_SOLID is rebuilt from the operation's result, and per-component face names are propagated for exporters and TiGLCreator picking.

The pairwise intersection-curve computation (used only for the seam overlay in exports and in TiGLCreator's fused-aircraft view, not for the fused solid itself) was reworked so each curve is trimmed against every other component, avoiding stray untrimmed seam wires. This computation is also now performed lazily, only when a caller actually requests it via Intersections(), instead of unconditionally inside Perform() - this alone roughly halves the regression test's runtime and speeds up every other caller that only needs the fused solid. The overlay in TiGLCreator was removed to make the fused visualization faster.

How Has This Been Tested?

• Added a regression test to tests/integrationtests/testSiblingComponentFuse.cpp with a realistic test geometry where
  fuselage, HTP and VTP all pairwise intersect near the tail. The test checks that the fused shape is topologically valid and has no internal/buried faces.
• Manually verified the fused export end to end via TIGLCreator'
  aircraft fused (slow)" draw action

Screenshots, that help to understand the changes(if applicabl

Checklist for PR Author:

• Unit or integration test added (if applicable)
• Python interface updated (if applicable)
• Python test added (if Python interface updated)
• Doxygen docstrings added
• ChangeLog.md updated

---

Disclaimer: Parts of this PR were developed with the assistance
(Anthropic's AI coding agent). I have reviewed, tested, and manu
all changes myself before submitting.

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Differences in fuse behavior on main and the pr branch

• C23 from digital hangar is missing tailplane after fuse

  

  On main:

  

  Both versions aren't correct

• D250-TF-2040 from digital hangar

  

  On main (or more precisely on 1388 crash when usind draw fused aircraft triangulation #1389)

  

• Similar issue on main but not on this branch for D250-TFLH2-MHEP-2040 from digital hangar.

I suggest to merge this. From the randomly selected CPACS files the behavior on this branch seems more robust. The C23 has issues both on main and on this branch. This should be examined as part of a separate issue.

[github-actions]

PR Reminders

This PR has changes in src/, TIGLCreator/, and tests/integrationtests/ but not in tests/unittests/, tests/python/, or bindings/python_internal/. ChangeLog.md has changes.

• 💡 Tip: Please check if new classes need to be added to the Python bindings

---

This is an automated reminder from CI

[codecov]

Codecov Report

❌ Patch coverage is 93.90244% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.19%. Comparing base (76802f0) to head (15bffb8).

Files with missing lines	Patch %	Lines
src/configuration/CTiglFusePlane.cpp	93.67%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1384      +/-   ##
==========================================
- Coverage   73.21%   73.19%   -0.03%     
==========================================
  Files         324      324              
  Lines       28556    28594      +38     
==========================================
+ Hits        20908    20928      +20     
- Misses       7648     7666      +18     

Flag	Coverage Δ
unittests	73.19% <93.90%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/control_devices/CCPACSControlSurfaces.cpp	95.83% <ø> (ø)
src/cpacs_other/CTiglUIDManager.cpp	86.23% <100.00%> (-1.21%)	⬇️
src/cpacs_other/CTiglUIDManager.h	100.00% <ø> (ø)
src/wing/CCPACSWing.cpp	84.93% <ø> (ø)
src/configuration/CTiglFusePlane.cpp	95.45% <93.67%> (-1.46%)	⬇️

... and 2 files with indirect coverage changes

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[ole-alb]

Thank you for that really cool fix. Looks very good. I also tried some configs and everything worked as intended.
Could we also use that OCC-Fuse and completely get rid of CFuseShapes? I think we don't use it a lot.

[joergbrech]

Could we also use that OCC-Fuse and completely get rid of CFuseShapes? I think we don't use it a lot.

Maybe. Its still used in examples, unit tests and, most critically, in the duct and control surface code. I suppose we could remove it, but I suggest as part of a separate issue. What do you think?

grep -r CFuseShapes * in src gives

boolean_operations/CFuseShapes.cpp:#include "CFuseShapes.h"
boolean_operations/CFuseShapes.cpp:CFuseShapes::CFuseShapes(const PNamedShape parent, const ListPNamedShape &childs)
boolean_operations/CFuseShapes.cpp:CFuseShapes::~CFuseShapes()
boolean_operations/CFuseShapes.cpp:const PNamedShape CFuseShapes::NamedShape()
boolean_operations/CFuseShapes.cpp:CFuseShapes::operator PNamedShape()
boolean_operations/CFuseShapes.cpp:const ListPNamedShape &CFuseShapes::Intersections()
boolean_operations/CFuseShapes.cpp:const ListPNamedShape &CFuseShapes::TrimmedChilds()
boolean_operations/CFuseShapes.cpp:const PNamedShape CFuseShapes::TrimmedParent()
boolean_operations/CFuseShapes.cpp:void CFuseShapes::Perform()
boolean_operations/CFuseShapes.cpp:void CFuseShapes::Clear()
boolean_operations/CFuseShapes.cpp:void CFuseShapes::DoFuse()
boolean_operations/CFuseShapes.h: * @brief CFuseShapes Implement a fuse, where the childs are fused with the parent
boolean_operations/CFuseShapes.h:class CFuseShapes
boolean_operations/CFuseShapes.h:    TIGL_EXPORT CFuseShapes(const PNamedShape parent, const ListPNamedShape& childs);
boolean_operations/CFuseShapes.h:    TIGL_EXPORT virtual ~CFuseShapes();
control_devices/CCPACSControlSurfaces.cpp:                    fusedBoxes = CFuseShapes(fusedBoxes, childs);
control_devices/CCPACSControlSurfaces.cpp:                fusedBoxes = CFuseShapes(fusedBoxes, childs);
ducts/CCPACSDuctAssembly.cpp:#include "CFuseShapes.h"
ducts/CCPACSDuctAssembly.cpp:    tool = CFuseShapes(parentDuct, childDucts);