Sample code for https://github.com/NetTopologySuite/NetTopologySuite/issues/434

convexhullexample.cs

using System.Collections.Generic;
using System.Globalization;
using System.IO;
using NetTopologySuite.Algorithm;
using NetTopologySuite.Geometries;
using NetTopologySuite.IO;
using NetTopologySuite.Simplify;
using NUnit.Framework;

namespace NetTopologySuite.Samples.Geometries
{
    public class convexhullexample
    {

        public void TestConvexHull1()
        {
            var rdr = new WKTReader();
            var g = rdr.Read("Wkt");
            var pts = g.Coordinates;
            var ch = new Algorithm.ConvexHull(pts, g.Factory);

            var ch1 = g.ConvexHull();
            Assert.AreEqual(ch.GetConvexHull(), ch1);
            pts = ch1.Coordinates;
            Assert.IsTrue(Orientation.IsCCW(ch1.Coordinates));

            var ch3 = TopologyPreservingSimplifier.Simplify(ch1, 1e-6);
            TestContext.WriteLine(ch1.NumPoints);
            TestContext.WriteLine(ch1.AsText());
            TestContext.WriteLine();
            //TestContext.WriteLine(ch2.AsText());
            //TestContext.WriteLine();
            TestContext.WriteLine(ch3.AsText());
        }

[TestCase(@"D:\obe\Downloads\border.txt")]
[TestCase(@"D:\obe\Downloads\s22a.xyz")]
public void TestFiles(string filePath)
{
    var pts = ReadFile(filePath);
    var convexHullOp = new ConvexHull(pts, GeometryFactory.Default);
    var ch = convexHullOp.GetConvexHull();

    Assert.That(ch, Is.Not.Null);
    TestContext.WriteLine($"ConvexHull ({Path.GetFileName(filePath)}):");
    TestContext.WriteLine("Geometry type: {0}", ch.GeometryType);
    TestContext.WriteLine("Number of points: {0}", ch.NumPoints);
    if (ch is Polygon p)
    {
        var ring = (LinearRing) p.ExteriorRing;
        TestContext.WriteLine("Exterior ring orientation: {0}", ring.IsCCW ? "counter-clockwise" : "clockwise");
    }
    var wktWriter = new WKTWriter {Formatted = true, MaxCoordinatesPerLine = 3, OutputOrdinates = Ordinates.XY};
    TestContext.WriteLine("WKT:\n{0}", wktWriter.WriteFormatted(ch));

    var simplifyOp = new TopologyPreservingSimplifier(ch) { DistanceTolerance = 1E-6 };
    var ch1 = simplifyOp.GetResultGeometry();
    TestContext.WriteLine("\nSimplified ConvexHull:");
    TestContext.WriteLine("Geometry type: {0}", ch1.GeometryType);
    TestContext.WriteLine("Number of points: {0}", ch1.NumPoints);
    if (ch1 is Polygon p1)
    {
        var ring = (LinearRing)p1.ExteriorRing;
        TestContext.WriteLine("Exterior ring orientation: {0}", ring.IsCCW ? "counter-clockwise" : "clockwise");
    }

    TestContext.WriteLine("WKT:\n{0}", wktWriter.WriteFormatted(ch1));

}

private IReadOnlyList<Coordinate> ReadFile(string filePath)
{
    if (!System.IO.File.Exists(filePath))
        throw new InconclusiveException($"File not present: '{filePath}'");

    using var sr = new StreamReader(File.OpenRead(filePath));
    var res = new List<Coordinate>();
    while (!sr.EndOfStream)
    {
        string line = sr.ReadLine();
        if (string.IsNullOrWhiteSpace(line))
            continue;

        string[] parts = line.Split(",");
        if (parts.Length < 2)
            throw new InvalidDataException();
        res.Add(new Coordinate(double.Parse(parts[0], NumberFormatInfo.InvariantInfo),
            double.Parse(parts[1], NumberFormatInfo.InvariantInfo)));
    }

    return res;
}
    }
}

gistfile1.txt

using System.Collections.Generic;
using System.Globalization;
using System.IO;
using NetTopologySuite.Algorithm;
using NetTopologySuite.Geometries;
using NetTopologySuite.IO;
using NetTopologySuite.Simplify;
using NUnit.Framework;

namespace NetTopologySuite.Samples.Geometries
{
    public class convexhullexample
    {

        public void TestConvexHull1()
        {
            var rdr = new WKTReader();
            var g = rdr.Read("Wkt");
            var pts = g.Coordinates;
            var ch = new Algorithm.ConvexHull(pts, g.Factory);

            var ch1 = g.ConvexHull();
            Assert.AreEqual(ch.GetConvexHull(), ch1);
            pts = ch1.Coordinates;
            Assert.IsTrue(Orientation.IsCCW(ch1.Coordinates));

            var ch3 = TopologyPreservingSimplifier.Simplify(ch1, 1e-6);
            TestContext.WriteLine(ch1.NumPoints);
            TestContext.WriteLine(ch1.AsText());
            TestContext.WriteLine();
            //TestContext.WriteLine(ch2.AsText());
            //TestContext.WriteLine();
            TestContext.WriteLine(ch3.AsText());
        }

[TestCase(@"D:\obe\Downloads\border.txt")]
[TestCase(@"D:\obe\Downloads\s22a.xyz")]
public void TestFiles(string filePath)
{
    var pts = ReadFile(filePath);
    var convexHullOp = new ConvexHull(pts, GeometryFactory.Default);
    var ch = convexHullOp.GetConvexHull();

    Assert.That(ch, Is.Not.Null);
    TestContext.WriteLine($"ConvexHull ({Path.GetFileName(filePath)}):");
    TestContext.WriteLine("Geometry type: {0}", ch.GeometryType);
    TestContext.WriteLine("Number of points: {0}", ch.NumPoints);
    if (ch is Polygon p)
    {
        var ring = (LinearRing) p.ExteriorRing;
        TestContext.WriteLine("Exterior ring orientation: {0}", ring.IsCCW ? "counter-clockwise" : "clockwise");
    }
    var wktWriter = new WKTWriter {Formatted = true, MaxCoordinatesPerLine = 3, OutputOrdinates = Ordinates.XY};
    TestContext.WriteLine("WKT:\n{0}", wktWriter.WriteFormatted(ch));

    var simplifyOp = new TopologyPreservingSimplifier(ch) { DistanceTolerance = 1E-6 };
    var ch1 = simplifyOp.GetResultGeometry();
    TestContext.WriteLine("\nSimplified ConvexHull:");
    TestContext.WriteLine("Geometry type: {0}", ch1.GeometryType);
    TestContext.WriteLine("Number of points: {0}", ch1.NumPoints);
    if (ch1 is Polygon p1)
    {
        var ring = (LinearRing)p1.ExteriorRing;
        TestContext.WriteLine("Exterior ring orientation: {0}", ring.IsCCW ? "counter-clockwise" : "clockwise");
    }

    TestContext.WriteLine("WKT:\n{0}", wktWriter.WriteFormatted(ch1));

}

private IReadOnlyList<Coordinate> ReadFile(string filePath)
{
    if (!System.IO.File.Exists(filePath))
        throw new InconclusiveException($"File not present: '{filePath}'");

    using var sr = new StreamReader(File.OpenRead(filePath));
    var res = new List<Coordinate>();
    while (!sr.EndOfStream)
    {
        string line = sr.ReadLine();
        if (string.IsNullOrWhiteSpace(line))
            continue;

        string[] parts = line.Split(",");
        if (parts.Length < 2)
            throw new InvalidDataException();
        res.Add(new Coordinate(double.Parse(parts[0], NumberFormatInfo.InvariantInfo),
            double.Parse(parts[1], NumberFormatInfo.InvariantInfo)));
    }

    return res;
}
    }
}