WIP - RESET THIS

scripts/orbits/IMassiveExtensions.cs

@@ -0,0 +1,4 @@
+public static class IMassiveExtensions
+{
+    public static double U(this IMassive m) => Kepler.U(m.Mass);
+}

scripts/orbits/IOrbit.cs

@@ -0,0 +1,7 @@
+using Vim.Math3d;
+
+public interface IOrbit
+{
+    Ellipse Ellipse { get; }
+    DVector3 GetPosition(float t);
+}

scripts/orbits/IOrbitalElementsExtensions.cs

@@ -0,0 +1,13 @@
+using Vim.Math3d;
+using static System.Math;
+
+public static class IOrbitalElementsExtensions
+{
+    /// <summary>
+    /// Get the Cartesian position on the orbit for a given mean anomaly.
+    /// </summary>
+    /// <param name="M">Mean anomaly</param>
+    /// <returns>Position</returns>
+    public static DVector2 GetEccentricPosition2D(this OrbitalElements elements, double M) =>
+        Kepler.GetEccentricPosition2D(elements.e, elements.a, M);
+}

scripts/orbits/Orbit.cs

@@ -2,7 +2,7 @@ using Godot;
 using System;
 using Vim.Math3d;
 
-public class Orbit
+public class Orbit : IOrbit
 {
     // The position of the primary body relative to the ellipse - the 
     // orbit itself is presented as being centred on the primary, but

scripts/orbits/OrbitalElements.cs

@@ -0,0 +1,46 @@
+public struct OrbitalElements
+{
+    private Ellipse _ellipse;
+    /// <summary>
+    /// Semi-major axis in AU
+    /// </summary>
+    public double a => _ellipse.a;
+    /// <summary>
+    /// Eccentricity
+    /// </summary>
+    public double e => _ellipse.e;
+    /// <summary>
+    /// Inclination in degrees
+    /// </summary>
+    public double i { get; private set; }
+    /// <summary>
+    /// Argument of ascending node in degrees
+    /// </summary>
+    public double W { get; private set; }
+    /// <summary>
+    /// Argument of periapsis in degrees
+    /// </summary>
+    public double p { get; private set; }
+    /// <summary>
+    /// Mean anomaly at epoch
+    /// </summary>
+    public double M0 { get; private set; }
+
+    /// <summary>
+    ///
+    /// </summary>
+    /// <param name="a">Semi-major axis in AU</param>
+    /// <param name="e">eccentricity</param>
+    /// <param name="i">Inclination in degrees</param>
+    /// <param name="W">Argument of ascending node in degrees</param>
+    /// <param name="p">Argument of periapsis in degrees</param>
+    /// <param name="M0">Mean anomaly at epoch</param>
+    public OrbitalElements(double a, double e, double i, double W, double p, double M0)
+    {
+        _ellipse = new Ellipse(a, e);
+        this.i = i;
+        this.W = W;
+        this.p = p;
+        this.M0 = M0;
+    }
+}