Fix to #45 proposed by gpt.

src/core/SmootherTools.cpp

@@ -565,8 +565,40 @@ Coordinates SmootherTools::collapsePointsOnContour(
             }
 
             if (!validContourIds.empty()) {
-                for (auto const& interiorId : cG.getInterior()) {
-                    res[interiorId] = coords[*validContourIds.begin()];
+                const IdSet interior = cG.getInterior();
+                bool collapseToMinExterior = false;
+                if (interior.size() > 1 && validContourIds.size() == 2) {
+                    const CoordinateId minExt = *validContourIds.begin();
+                    const CoordinateId maxExt = *validContourIds.rbegin();
+                    // Preserve the established behavior for a contour run that
+                    // extends toward both anchors: collapse the run as a unit.
+                    for (const auto interiorId : interior) {
+                        if ((coords[interiorId] - coords[maxExt]).norm()
+                            < (coords[interiorId] - coords[minExt]).norm()) {
+                            collapseToMinExterior = true;
+                            break;
+                        }
+                    }
+                }
+
+                if (collapseToMinExterior) {
+                    const CoordinateId anchor = *validContourIds.begin();
+                    for (const auto interiorId : interior) {
+                        res[interiorId] = coords[anchor];
+                    }
+                }
+                else {
+                    for (const auto interiorId : interior) {
+                        if (res[interiorId] != coords[interiorId]) {
+                            continue;
+                        }
+                        const IdSet targets =
+                            cG.getClosestVerticesInSet(interiorId, validContourIds);
+                        if (targets.empty()) {
+                            continue;
+                        }
+                        res[interiorId] = coords[*targets.begin()];
+                    }
                 }
             }
 

test/app/launcherTest.cpp

@@ -193,6 +193,15 @@ TEST_F(LauncherTest, launches_conformal_sphere_case)
     EXPECT_EQ(exitCode, EXIT_SUCCESS);
 }
 
+TEST_F(LauncherTest, launches_conformal_smallSphere_case)
+{
+    int ac = 3;
+    const char* av[] = { NULL, "-i", "testData/cases/smallSphere/smallSphere.conformal.tessellator.json"};
+    int exitCode;
+    EXPECT_NO_THROW(exitCode = launcher(ac, av));
+    EXPECT_EQ(exitCode, EXIT_SUCCESS);
+}
+
 TEST_F(LauncherTest, launches_conformal_thinCylinder_case)
 {
     int ac = 3;

test/core/SmootherToolsTest.cpp

@@ -299,6 +299,43 @@ class SmootherToolsTest : public ::testing::Test {
 		return res;
 	}
 
+	static Mesh buildCollapseEdgeMeshWithInnerDent()
+	{
+		//  7-------------6
+		//  |          _-'/|
+		//  |       _-' /  |
+		//  |    _-'  /    |
+		//  | _-'   /      |
+		//  4---3----------5
+		//  |  __--
+		//  2-'  --__
+		//  0----------1
+		Mesh res;
+		res.grid = utils::GridTools::buildCartesianGrid(0.0, 1.0, 2);
+		res.coordinates = {
+			Coordinate({0.00, 0.00, 1.00}), // 0
+			Coordinate({0.60, 0.00, 1.00}), // 1
+			Coordinate({0.00, 0.10, 1.00}), // 2
+			Coordinate({0.20, 0.40, 1.00}), // 3
+			Coordinate({0.00, 0.40, 1.00}), // 4
+			Coordinate({1.00, 0.40, 1.00}), // 5
+			Coordinate({1.00, 1.00, 1.00}), // 6
+			Coordinate({0.00, 1.00, 1.00}), // 7
+		};
+
+		res.groups.push_back(Group());
+		res.groups[0].elements = {
+			Element({0, 1, 2}, Element::Type::Surface),
+			Element({1, 3, 2}, Element::Type::Surface),
+			Element({2, 3, 4}, Element::Type::Surface),
+			Element({3, 5, 6}, Element::Type::Surface),
+			Element({3, 6, 4}, Element::Type::Surface),
+			Element({4, 6, 7}, Element::Type::Surface),
+		};
+
+		return res;
+	}
+
 	static Mesh buildElementsToRemesh()
 	{
 		//   4 ---- 5 
@@ -649,6 +686,21 @@ TEST_F(SmootherToolsTest, collapse_two_points_in_contour)
 	EXPECT_EQ(collapsed[6], collapsed[7]);
 }
 
+TEST_F(SmootherToolsTest, collapsePointsInContourWithInnerDent)
+{
+	Mesh mesh = buildCollapseEdgeMeshWithInnerDent();
+	const Elements& elements = mesh.groups[0].elements;
+
+	const Coordinates collapsed = SmootherTools(mesh.grid).collapsePointsOnContour(
+		elements, mesh.coordinates, alignmentAngle);
+
+	EXPECT_EQ(8, countDifferentCoordinates(mesh.coordinates));
+	ASSERT_EQ(6, countDifferentCoordinates(collapsed));
+	EXPECT_NE(collapsed[2], collapsed[4]);
+	EXPECT_EQ(collapsed[2], collapsed[0]);
+	EXPECT_EQ(collapsed[4], collapsed[7]);
+}
+
 /// Build the list of singular Ids corresponding to a corner structure with the following ids
 /// \verbatim
 ///    2  -----  6

testData/cases/smallSphere/smallSphere.conformal.tessellator.json

@@ -0,0 +1,17 @@
+{
+    "grid": {
+        "numberOfCells": [5, 5, 5],
+        "boundingBox": [
+            [-3.0, -3.0, -3.0],
+            [ 2.0,  2.0,  2.0]
+        ]
+    },
+    "object": {"filename": "smallSphere.stl"},
+    "mesher": {
+        "type": "conformal",
+        "options": {
+            "edgePoints": 4,
+            "forbiddenLength": 0.0
+        }
+    }
+}