1 files changed, 24 insertions, 5 deletions
diff --git a/PositionCalculator.cs b/PositionCalculator.cs
index 4344e76..2140a88 100644
--- a/PositionCalculator.cs
+++ b/PositionCalculator.cs
@@ -1,16 +1,33 @@
 using CoordinateSharp;
-using PagerParser;
-using System;
 using System.ComponentModel.DataAnnotations.Schema;
+using System.Text.Json.Serialization;
 using System.Text.RegularExpressions;
 
 namespace PagerParser;
 
 public class GpsPosition {
+    [JsonIgnore]
     [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
     public int    GpsPositionId { get; set; }
     public double Latitude      { get; set; }
     public double Longitude     { get; set; }
+
+    private const double EarthRadius = 6_371;
+
+    /// <summary>
+    /// Get the distance from this point to the specified coordinates
+    /// </summary>
+    public double GetDistance(double latitude, double longitude) =>
+        Math.Acos(
+            Math.Sin(Latitude) * Math.Sin(latitude) +
+            Math.Cos(Latitude) * Math.Cos(latitude) *
+            Math.Cos(longitude - Longitude)) * EarthRadius;
+
+    /// <summary>
+    /// Get the distance from this point to another
+    /// </summary>
+    public double GetDistance(GpsPosition position) =>
+        GetDistance(position.Latitude, position.Longitude);
 }
 
 public record MelwaysPage {
@@ -56,13 +73,15 @@ public class PositionCalculator {
     };
 
     public static GpsPosition? GetGpsPosition(ParsedPagerMessage message) {
-        if(message.MelwaysMapNo is null || message.MelwaysGrid is null)
+        if(message.MapType != MapType.Melways)
+            return null;
+        if(message.MapNo is null || message.MapGrid is null)
             return null;
-        var page = MelwaysPages.FirstOrDefault(p => p.PageNo == message.MelwaysMapNo);
+        var page = MelwaysPages.FirstOrDefault(p => p.PageNo == message.MapNo);
         if(page is null)
             return null;
 
-        var match = Regex.Match(message.MelwaysGrid.ToUpper(), "^([A-HJ-K])([0-9]+)$");
+        var match = Regex.Match(message.MapGrid.ToUpper(), "^([A-HJ-K])([0-9]+)$");
         if(!match.Success)
             return null;