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GRIDEDIT-2306: Skip hanging edges in mesh boundary calculation #546

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Merged
priscavdsluis merged 1 commit into from
Oct 1, 2026
Merged

GRIDEDIT-2306: Skip hanging edges in mesh boundary calculation #546

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16 changes: 8 additions & 8 deletions libs/MeshKernel/src/MeshBoundaryExtractor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -289,9 +289,11 @@ void meshkernel::MeshBoundaryExtractor::FindAllBoundarEdges(const std::vector<Po
for (UInt count = 0; count < edges.size(); ++count)
{

if (edgesFaces[count][1] != constants::missing::uintValue || !IsValidEdge(edges[count]))
if (!IsValidEdge(edges[count]) ||

@andreasbuykx andreasbuykx Oct 1, 2026

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I think the edgesFaces pair is a sorted pair? And thus these lines mean: if the first is uintValue (which is max-int, indicating no face) then the next must be too so no faces, if the last edge is not uintValue (valid face) then the first must also be, so this is an interior edge.

It would be helpful to have a little helper function IsBoundaryEdge that hides this logic, and maybe adds a comment that explains the logic.

@RStolkerDeltares RStolkerDeltares Oct 1, 2026

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The edge-face pair contains the edge adjacent face id's.

AI overview:

edgesFaces[count][0] — the first face adjacent to the edge. For a boundary edge (an edge with only one neighbouring face), this is always populated with that one valid face id. It's populated for essentially every edge that touches at least one face.

edgesFaces[count][1] — the second face adjacent to the edge, only set if the edge is shared between two faces (i.e. an interior edge). If the edge has only one adjacent face (boundary edge) or no adjacent face (a dangling/hanging edge not part of any face), this slot is constants::missing::uintValue.

So the convention used throughout this file is:

[0] [1] meaning
valid valid interior edge, shared by two faces
valid missing boundary edge, touches exactly one face
missing missing edge belongs to no face at all ("hanging" edge)

edgesFaces[count][0] == constants::missing::uintValue ||
edgesFaces[count][1] != constants::missing::uintValue)
{
// Edge is either invalid or not on boundary
// Edge is invalid, has no adjacent face (hanging edge), or is interior (two faces)
continue;
}

Expand Down Expand Up @@ -366,12 +368,10 @@ void meshkernel::MeshBoundaryExtractor::FindBoundaryPolygons(const std::vector<P
for (UInt count = 0; count < edges.size(); ++count)
{

if (!IsValidEdge(edges[count]))
{
continue;
}

if (edgesFaces[count][1] != constants::missing::uintValue || edgeVisited[count])
if (edgeVisited[count] ||
!IsValidEdge(edges[count]) ||
edgesFaces[count][0] == constants::missing::uintValue ||
edgesFaces[count][1] != constants::missing::uintValue)
{
continue;
}
Expand Down
36 changes: 36 additions & 0 deletions libs/MeshKernel/tests/src/Mesh2DTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -423,6 +423,42 @@ TEST(Mesh2D, HangingEdge)
ASSERT_EQ(1, mesh.GetNumFaces());
}

TEST(Mesh2D, MeshBoundaryToPolygonWithHangingEdge)
{
// 1 Setup
std::vector<meshkernel::Point> nodes;
nodes.push_back({0.0, 0.0});
nodes.push_back({5.0, 0.0});
nodes.push_back({3.0, 2.0});
nodes.push_back({3.0, 4.0});

std::vector<meshkernel::Edge> edges;
edges.push_back({0, 1});
edges.push_back({1, 3});
edges.push_back({3, 0});
edges.push_back({2, 1});

auto mesh = meshkernel::Mesh2D(meshkernel::Projection::cartesian);
mesh.SetNodes(nodes);
mesh.SetEdges(edges);
mesh.Administrate();

std::vector<meshkernel::Point> polygonNodes;

// 2 Execution
auto meshBoundaryPolygon = mesh.ComputeBoundaryPolygons(polygonNodes);

// 3 Validation
const double tolerance = 1e-5;
ASSERT_EQ(4, meshBoundaryPolygon.size());

for (const auto& point : meshBoundaryPolygon)
{
const double distanceToHangingNode = std::hypot(point.x - nodes[2].x, point.y - nodes[2].y);
EXPECT_GT(distanceToHangingNode, tolerance);
}
}

TEST(Mesh2D, NodeMerging)
{
// 1. Setup
Expand Down
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