NMEA 0183 sentence parser/builder

using System;using System.Drawing;
using System.Windows.Forms;

namespace GNSSView
{
    // Code by Aleksandr Dikarev, dikarev-aleksandr@yandex.ru
    public struct GeoCoordinate2D
    {
        public double Latitude;
        public double Longitude;
    }

    public partial class GeoPlot : UserControl
    {
        #region Properties

        int maxPoints = 10;
        FixedSizeLIFO<GeoCoordinate2D> points;

        Pen pointPen = new Pen(Brushes.Blue, 2.0f);
        Pen gridPen = new Pen(Brushes.Black, 1.0f);

        #endregion

        #region Constructor

        public GeoPlot()
        {
            InitializeComponent();
        }

        #endregion

        #region Methods

        public void Init(int trajectoryLength)
        {
            maxPoints = trajectoryLength;
            points = new FixedSizeLIFO<GeoCoordinate2D>(maxPoints);
        }

        public void AddPoint(GeoCoordinate2D newPoint)
        {
            points.Add(newPoint);
        }

        public static void GetCurveLengths(out double byMeridian, out double byParallel, double lat1, double lon1, double lat2, double lon2)
        {                        
            double majAxis = 6378137.0;

            double invFlt = 298.257223563;
            double flt = 1 / invFlt;
            double minAxis = majAxis * (1 - flt);
            double ellE2 = 1 - minAxis * minAxis / majAxis / majAxis;
                                 
            double avrLatitude = (lat2 + lat1) / 2.0;
            
            double W = Math.Sqrt(1 - ellE2 * Math.Sin(avrLatitude * Math.PI / 180) * Math.Sin(avrLatitude * Math.PI / 180));
            double ecrM = majAxis * (1 - ellE2) / W / W / W;
            double ecrN = majAxis / W;

            byMeridian = ecrM * (lat2 - lat1) * Math.PI / 180.0;
            byParallel = ecrN * Math.Cos(avrLatitude * Math.PI / 180) * (lon2 - lon1) * Math.PI / 180.0;
        }

        private static double GetDistance2DM(double lat1, double lon1, double lat2, double lon2)
        {
            double xl, yl;
            GetCurveLengths(out xl, out yl, lat1, lon1, lat2, lon2);

            return Math.Sqrt(xl * xl + yl * yl);
        }

        #endregion
        
        #region Handlers

        private void GeoPlot_Paint(object sender, PaintEventArgs e)
        {
            e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;

            if ((points != null) && (!e.ClipRectangle.IsEmpty))
            {
                var items = points.ToArray();

                if (items.Length > 1)
                {
                    double meanLat = items[0].Latitude;
                    double meanLon = items[0].Longitude;
                    
                    double farestLat = 0.0;
                    double farestLon = 0.0;

                    for (int i = 0; i < items.Length; i++)
                    {
                        if (Math.Abs(items[i].Latitude - meanLat) > farestLat)
                            farestLat = Math.Abs(items[i].Latitude - meanLat);

                        if (Math.Abs(items[i].Longitude - meanLon) > farestLon)
                            farestLon = Math.Abs(items[i].Longitude - meanLon);
                    }

                    double farestDist = Math.Max(farestLat, farestLon);


                    if (farestDist < double.Epsilon)
                        farestDist = 0.000001;

                    double xScale = e.Graphics.ClipBounds.Width / (farestDist * 2.0f);
                    double yScale = e.Graphics.ClipBounds.Height / (farestDist * 2.0f);

                    float scale = (float)Math.Min(xScale, yScale);

                    e.Graphics.TranslateTransform(e.ClipRectangle.Width / 2.0f, e.ClipRectangle.Height / 2.0f);

                    float fDist = Math.Abs((float)farestDist * 0.75f);
                    double fDistM = GetDistance2DM(meanLat, meanLon, meanLat + fDist, meanLon + fDist);
                    float fDistScaled = (float)(fDist * scale);

                    e.Graphics.DrawLine(gridPen, -fDistScaled, -4, -fDistScaled, 4);
                    e.Graphics.DrawLine(gridPen, fDistScaled, -4, fDistScaled, 4);
                    e.Graphics.DrawLine(gridPen, -4, -fDistScaled, 4, -fDistScaled);
                    e.Graphics.DrawLine(gridPen, -4, fDistScaled, 4, fDistScaled);

                    var fDistMLbl = fDistM.ToString("0.0 m");
                    var fDistMLblSize = e.Graphics.MeasureString(fDistMLbl, this.Font);

                    e.Graphics.DrawString(fDistMLbl, this.Font, Brushes.Black,
                        -fDistScaled - fDistMLblSize.Width / 2, -fDistMLblSize.Height - 2);

                    e.Graphics.DrawString(fDistMLbl, this.Font, Brushes.Black,
                        fDistScaled - fDistMLblSize.Width / 2, -fDistMLblSize.Height - 2);

                    e.Graphics.DrawString(fDistMLbl, this.Font, Brushes.Black,
                        -fDistMLblSize.Width, -fDistScaled - fDistMLblSize.Height / 2);

                    e.Graphics.DrawString(fDistMLbl, this.Font, Brushes.Black,
                        -fDistMLblSize.Width, fDistScaled - fDistMLblSize.Height / 2);

                    float left = -e.ClipRectangle.Width / 2.0f;
                    float right = e.ClipRectangle.Width / 2.0f;
                    float top = -e.ClipRectangle.Height / 2.0f;
                    float bottom = e.ClipRectangle.Height / 2.0f;

                    e.Graphics.DrawLine(gridPen, left, 0.0f, right, 0.0f);
                    e.Graphics.DrawLine(gridPen, 0.0f, top, 0.0f, bottom);                 

                    
                    PointF[] pointsToDraw = new PointF[items.Length];
                    for (int i = 0; i < items.Length; i++)
                    {
                        float x = (float)(items[i].Longitude - meanLon) * scale;
                        float y = (float)(items[i].Latitude - meanLat) * scale;

                        pointsToDraw[i] = new PointF(x, y);
                    }
                    e.Graphics.DrawLines(pointPen, pointsToDraw);

                    var latLabel = StrUtils.AngleToString(meanLat);
                    var latLabelSize = e.Graphics.MeasureString(latLabel, this.Font);
                    var lonLabel = StrUtils.AngleToString(meanLon);
                    var lonLabelSize = e.Graphics.MeasureString(lonLabel, this.Font);

                    e.Graphics.DrawString(latLabel, this.Font, Brushes.Black, right - lonLabelSize.Width, 2.0f);
                    e.Graphics.DrawString(lonLabel, this.Font, Brushes.Black, 5.0f, top + 2.0f);
                }
            }           
        }

        private void GeoPlot_Resize(object sender, EventArgs e)
        {
            Invalidate();
        }

        #endregion
    }
}