Feature: OpenFOAM reader [2/n] - Hex meshes without connectivity by sandro-elsweijer · Pull Request #2258 · DLR-AMR/t8code

sandro-elsweijer · 2026-04-01T13:59:15Z

Describe your changes here:
This PR adds the feature to read OpenFOAM hex only meshes without connectivity.
The internal data structures of the reader are used to assemble hex cells and add them to a cmesh.
The provided example can now be used to read a hex mesh like the mesh from the pitzDailySteady OpenFOAM example.

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The author made sure that, as a reviewer, he/she would check all boxes below.

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As a reviewer please read through all the code lines and make sure that the code is fully understood, bug free, well-documented and well-structured.

General

The reviewer executed the new code features at least once and checked the results manually.
The code follows the t8code coding guidelines.
New source/header files are properly added to the CMake files.
The code is well documented. In particular, all function declarations, structs/classes and their members have a proper doxygen documentation. Make sure to add a file documentation for each file!
All new algorithms and data structures are sufficiently optimal in terms of memory and runtime (If this should be merged, but there is still potential for optimization, create a new issue).

Tests

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If the Pull request introduces code that is not covered by the github action (for example coupling with a new library):

Should this use case be added to the github action?
If not, does the specific use case compile and all tests pass (check manually).

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If a new directory with source files is added, it must be covered by the scripts/internal/find_all_source_files.sh to check the indentation of these files.
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License

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codecov · 2026-06-24T08:44:06Z

Codecov Report

❌ Patch coverage is 0% with 142 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.21%. Comparing base (2e9b7f5) to head (dcdf556).
⚠️ Report is 84 commits behind head on main.

Files with missing lines	Patch %	Lines
src/t8_openfoam/t8_openfoam_reader.cxx	0.00%	98 Missing ⚠️
src/t8_openfoam/t8_openfoam_reader.hxx	0.00%	44 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2258      +/-   ##
==========================================
- Coverage   81.74%   81.21%   -0.53%     
==========================================
  Files         126      127       +1     
  Lines       20702    20836     +134     
==========================================
  Hits        16922    16922              
- Misses       3780     3914     +134

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spenke91

Sorry it took so lonf until I found time for the review...

Great to see you are making progress here! 🥳
I only have a bunch of minor suggestions and questions. For the hex construction, I admit I had a hard time following every single step in detail, but I am happy to have a more detailed look next time :-)

spenke91 · 2026-06-25T12:22:12Z

-  error = error && !read_faces (case_faces_file);
-  error = error && !read_owner (case_owner_file);
-  error = error && !read_neighbor (case_neighbor_file);
+  bool success = 1;


I am getting used to using 0 and 1 for bool, but can't we at least use true for initializing bools? 😆

Suggested change

bool success = 1;

bool success = true;

spenke91 · 2026-07-21T09:18:11Z

+   * \return              The eclass of the cell
+   */
+  t8_eclass_t
+  get_cell_eclass (const size_t cell_id)


Sorry to play that card again, but why is this function's implementation in the header, not the source file? 🤓

spenke91 · 2026-07-21T09:22:41Z

+    /* OpenFOAM only has 3D cells, so we do not check 0-2 dimensional cells. */
+    switch (m_cell_faces[cell_id].size ()) {
+    case 4:
+      /* This cell is hopefully a tet with 4*3=12 points. */


Suggested change

/* This cell is hopefully a tet with 4*3=12 points. */

/* This cell should be a tet with 4*3=12 points. */

spenke91 · 2026-07-21T09:23:24Z

+      num_points += m_face_points[face.first].size ();
+    }
+
+    /* OpenFOAM only has 3D cells, so we do not check 0-2 dimensional cells. */


Suggested change

/* OpenFOAM only has 3D cells, so we do not check 0-2 dimensional cells. */

// Distinguish shapes based on the number of faces and points.

// Note: OpenFOAM only has 3D cells, so we do not check 0-2 dimensional cells.

spenke91 · 2026-07-21T09:24:22Z

+        return T8_ECLASS_PYRAMID;
+      break;
+    case 6:
+      /* This cell is hopefully a hex with 6 * 4 = 24 points. */


Suggested change

/* This cell is hopefully a hex with 6 * 4 = 24 points. */

/* This cell should be a hex with 6 * 4 = 24 points. */

But if you prefer, you can also stick to hopefully, it is funnier ;-)

spenke91 · 2026-07-21T10:19:23Z

+     * the next vertex is vertex 1 and therefore vertex 0 of face 1. Otherwise, the previous point is vertex 0 of face 1.
+     * We iterate cyclic over the face vertices. So if we arrive at the end, we begin at the start. */
+  auto next_vertex
+    = (found_face_0_vertex_0 + 1) == check_face->end () ? check_face->begin () : found_face_0_vertex_0 + 1;


Suggested change

= (found_face_0_vertex_0 + 1) == check_face->end () ? check_face->begin () : found_face_0_vertex_0 + 1;

= ( (found_face_0_vertex_0 + 1) == check_face->end () ? check_face->begin () : found_face_0_vertex_0 + 1 );

spenke91 · 2026-07-21T10:21:04Z

+     * We iterate cyclic over the face vertices. So if we arrive at the end, we begin at the start. */
+  auto next_vertex
+    = (found_face_0_vertex_0 + 1) == check_face->end () ? check_face->begin () : found_face_0_vertex_0 + 1;
+  /* Check if face 0 contains this vertex */


It looks like it is searching through face 1 though?

spenke91 · 2026-07-21T10:21:24Z

+  }
+  else {
+    const auto previous_vertex
+      = found_face_0_vertex_0 == check_face->begin () ? check_face->end () : found_face_0_vertex_0 - 1;


Suggested change

= found_face_0_vertex_0 == check_face->begin () ? check_face->end () : found_face_0_vertex_0 - 1;

= (found_face_0_vertex_0 == check_face->begin () ? check_face->end () : found_face_0_vertex_0 - 1);

spenke91 · 2026-07-21T10:32:16Z

+  /* ------------------------- 4. Add remaining four faces ------------------------- */
+
+  /* Lastly, we have to match the rest of the faces so we can add the boundaries to the cmesh and
+     * to get the orientations and faces for neighbor linkage. */


Suggested change

* to get the orientations and faces for neighbor linkage. */

* to get the orientations and faces for neighbor linkage. */

spenke91 · 2026-07-21T10:33:24Z

+    //t8_face_normal = t8_eclass_face_orientation[eclass][1];
+    //orientation.second = (face_normals[*face_id] == t8_face_normal);


Suggested change

//t8_face_normal = t8_eclass_face_orientation[eclass][1];

//orientation.second = (face_normals[*face_id] == t8_face_normal);

sandro-elsweijer added 7 commits April 1, 2026 15:37

add ability to read OpenFOAM hex meshes without connectivity

7b4931f

Merge branch 'feature-openfoam_reader_0' into feature_openfoam-reader_1

82ad820

Merge branch 'feature-openfoam_reader_0' into feature_openfoam-reader_1

a6f1809

add back communicator

ec12bfe

Merge branch 'feature-openfoam_reader_0' into feature_openfoam-reader_1

d0290af

reintroduce comm

817e047

Merge branch 'feature-openfoam_reader_0' into feature_openfoam-reader_1

74e8d92

Base automatically changed from feature-openfoam_reader_0 to main June 23, 2026 11:23

sandro-elsweijer added 2 commits June 23, 2026 13:36

move implementation context to cxx

68f4b46

bugfix

dcdf556

sandro-elsweijer marked this pull request as ready for review June 24, 2026 08:25

sandro-elsweijer requested a review from spenke91 June 24, 2026 08:26

sandro-elsweijer assigned spenke91 Jun 24, 2026

spenke91 requested changes Jul 21, 2026

View reviewed changes

spenke91 assigned sandro-elsweijer and unassigned spenke91 Jul 21, 2026

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Feature: OpenFOAM reader [2/n] - Hex meshes without connectivity#2258

Feature: OpenFOAM reader [2/n] - Hex meshes without connectivity#2258
sandro-elsweijer wants to merge 9 commits into
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sandro-elsweijer commented Apr 1, 2026 •

edited by t8ddy

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	/* This cell is hopefully a tet with 43=12 points. /
	/* This cell should be a tet with 43=12 points. /

	/* OpenFOAM only has 3D cells, so we do not check 0-2 dimensional cells. */
	// Distinguish shapes based on the number of faces and points.
	// Note: OpenFOAM only has 3D cells, so we do not check 0-2 dimensional cells.

	/* This cell is hopefully a hex with 6 * 4 = 24 points. */
	/* This cell should be a hex with 6 * 4 = 24 points. */

	= (found_face_0_vertex_0 + 1) == check_face->end () ? check_face->begin () : found_face_0_vertex_0 + 1;
	= ( (found_face_0_vertex_0 + 1) == check_face->end () ? check_face->begin () : found_face_0_vertex_0 + 1 );

	= found_face_0_vertex_0 == check_face->begin () ? check_face->end () : found_face_0_vertex_0 - 1;
	= (found_face_0_vertex_0 == check_face->begin () ? check_face->end () : found_face_0_vertex_0 - 1);

	* to get the orientations and faces for neighbor linkage. */
	* to get the orientations and faces for neighbor linkage. */

		//t8_face_normal = t8_eclass_face_orientation[eclass][1];
		//orientation.second = (face_normals[*face_id] == t8_face_normal);

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sandro-elsweijer commented Apr 1, 2026 •

edited by t8ddy

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