using System;

using System.Linq;

using NetTopologySuite.Geometries;

using NetTopologySuite.Geometries.Utilities;

using NetTopologySuite.IO;

​

class Program

{

    static void Main(string[] args)

    {

        string wktLineString = "LINESTRING (0 0, 1 1, 2 2, 3 3, 4 4)";

        string wktPoint1 = "POINT (1.5 1.5)";

        string wktPoint2 = "POINT (3 3)";

​

        // Initialize WKT readers

        var wktReader = new WKTReader();

​

        // Parse the LineString and Points

        LineString lineString = (LineString)wktReader.Read(wktLineString);

        Point point1 = (Point)wktReader.Read(wktPoint1);

        Point point2 = (Point)wktReader.Read(wktPoint2);

​

        // Get the segment of the LineString between the two points

        LineSegment segment = GetLineSegmentBetweenPoints(lineString, point1, point2);

​

        // Output the segment as WKT

        string segmentWKT = segment.ToString();

        Console.WriteLine($"Segment between points:\n{segmentWKT}");

    }

​

    static LineSegment GetLineSegmentBetweenPoints(LineString lineString, Point point1, Point point2)

    {

        if (lineString == null || point1 == null || point2 == null)

        {

            throw new ArgumentNullException("Input geometries cannot be null.");

        }

​

        if (!lineString.Coordinates.Contains(point1.Coordinate) || !lineString.Coordinates.Contains(point2.Coordinate))

        {

            throw new ArgumentException("Both points must fall on the LineString.");

        }

​

        Coordinate[] coordinates = lineString.Coordinates;

​

        int index1 = Array.IndexOf(coordinates, point1.Coordinate);

        int index2 = Array.IndexOf(coordinates, point2.Coordinate);

​

        int startIndex = Math.Min(index1, index2);

        int endIndex = Math.Max(index1, index2);

​

        Coordinate[] segmentCoordinates = new Coordinate[endIndex - startIndex + 1];

        Array.Copy(coordinates, startIndex, segmentCoordinates, 0, segmentCoordinates.Length);

​

        return new LineSegment(segmentCoordinates[0], segmentCoordinates[segmentCoordinates.Length - 1]);

    }

}

​