Index: DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geometry/GeometryPointStringTests.cs
===================================================================
diff -u
--- DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geometry/GeometryPointStringTests.cs	(revision 0)
+++ DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geometry/GeometryPointStringTests.cs	(revision 4904)
@@ -0,0 +1,95 @@
+// Copyright (C) Stichting Deltares 2024. All rights reserved.
+// 
+// This file is part of the Dam Engine.
+// 
+// The Dam Engine is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+// 
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+// 
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using Deltares.DamEngine.Data.Geometry;
+using NUnit.Framework;
+
+namespace Deltares.DamEngine.Data.Tests.Geometry;
+
+[TestFixture]
+public class GeometryPointStringTests
+{
+    [Test]
+    public void GivenGeometryPointStringWithRedundantPoints_WhenRemovingUnnecessaryPoints_ThenCorrectGeometryPointStringReturned()
+    {
+        var geometryPointString = new GeometryPointString();
+        
+        // The polyline contains only 3 identical points => expected 1 point
+        geometryPointString.CalcPoints.Add(new Point2D(2, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(2, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(2, 3));
+        geometryPointString.RemoveUnnecessaryPoints();
+        Assert.That(geometryPointString.CalcPoints, Has.Count.EqualTo(1));
+        Assert.That(geometryPointString.CalcPoints[0].X, Is.EqualTo(2));
+        Assert.That(geometryPointString.CalcPoints[0].Z, Is.EqualTo(3));
+        
+        // The polyline contains 1 straight line with 3 points => expected 2 points
+        geometryPointString.CalcPoints.Clear();
+        geometryPointString.CalcPoints.Add(new Point2D(2, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(3, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(4, 3));
+        geometryPointString.RemoveUnnecessaryPoints();
+        Assert.That(geometryPointString.CalcPoints, Has.Count.EqualTo(2));
+        Assert.Multiple(() =>
+        {
+            Assert.That(geometryPointString.CalcPoints[0].X, Is.EqualTo(2));
+            Assert.That(geometryPointString.CalcPoints[0].Z, Is.EqualTo(3));
+            Assert.That(geometryPointString.CalcPoints[1].X, Is.EqualTo(4));
+            Assert.That(geometryPointString.CalcPoints[1].Z, Is.EqualTo(3));
+        });
+
+        // The polyline contains 1 straight line with 5 points => expected 2 points
+        geometryPointString.CalcPoints.Clear();
+        geometryPointString.CalcPoints.Add(new Point2D(2, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(3, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(4, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(5, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(6, 3));
+        geometryPointString.RemoveUnnecessaryPoints();
+        Assert.That(geometryPointString.CalcPoints, Has.Count.EqualTo(2));
+        Assert.Multiple(() =>
+        {
+            Assert.That(geometryPointString.CalcPoints[0].X, Is.EqualTo(2));
+            Assert.That(geometryPointString.CalcPoints[0].Z, Is.EqualTo(3));
+            Assert.That(geometryPointString.CalcPoints[1].X, Is.EqualTo(6));
+            Assert.That(geometryPointString.CalcPoints[1].Z, Is.EqualTo(3));
+        });
+        
+        // The polyline contains 2 straight lines with 5 points => expected 3 points
+        geometryPointString.CalcPoints.Clear();
+        geometryPointString.CalcPoints.Add(new Point2D(2, 3));
+        geometryPointString.CalcPoints.Add(new Point2D(3, 4));
+        geometryPointString.CalcPoints.Add(new Point2D(4, 5));
+        geometryPointString.CalcPoints.Add(new Point2D(5, 4));
+        geometryPointString.CalcPoints.Add(new Point2D(6, 3));
+        geometryPointString.RemoveUnnecessaryPoints();
+        Assert.That(geometryPointString.CalcPoints, Has.Count.EqualTo(3));
+        Assert.Multiple(() =>
+        {
+            Assert.That(geometryPointString.CalcPoints[0].X, Is.EqualTo(2));
+            Assert.That(geometryPointString.CalcPoints[0].Z, Is.EqualTo(3));
+            Assert.That(geometryPointString.CalcPoints[1].X, Is.EqualTo(4));
+            Assert.That(geometryPointString.CalcPoints[1].Z, Is.EqualTo(5));
+            Assert.That(geometryPointString.CalcPoints[2].X, Is.EqualTo(6));
+            Assert.That(geometryPointString.CalcPoints[2].Z, Is.EqualTo(3));
+        });
+    }
+}
\ No newline at end of file
Index: DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/GeometryPointString.cs
===================================================================
diff -u -r4897 -r4904
--- DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/GeometryPointString.cs	(.../GeometryPointString.cs)	(revision 4897)
+++ DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/GeometryPointString.cs	(.../GeometryPointString.cs)	(revision 4904)
@@ -695,7 +695,7 @@
 
         CondensePoints();
 
-        for (int i = calcPoints.Count - 2; i > 1; i--)
+        for (int i = calcPoints.Count - 2; i > 0; i--)
         {
             // if the slope of the line before the point is equal to the slope after the point, the point can be removed
             double slopeBefore = (calcPoints[i].Z - calcPoints[i - 1].Z) / (calcPoints[i].X - calcPoints[i - 1].X);