From ecf7147357fe0a048ae125a209f98e955d050eab Mon Sep 17 00:00:00 2001
From: arthomnix <arthomnix@arthomnix.dev>
Date: Fri, 3 Apr 2026 02:59:22 +0100
Subject: [PATCH] handle SOI changes correctly

---
 OemLoader/MainWindow.cs | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/OemLoader/MainWindow.cs b/OemLoader/MainWindow.cs
index 5f10686..5e5697f 100644
--- a/OemLoader/MainWindow.cs
+++ b/OemLoader/MainWindow.cs
@@ -12,7 +12,7 @@ public class MainWindow(string title)
     private readonly ImInputString _filename = new(short.MaxValue);
     private List<OemDataLine>? _oem;
     private string? _errorMessage;
-    private long _sliderTicks = 0;
+    private long _sliderTicks;
 
     private void GoToTime(DateTime time)
     {
@@ -20,9 +20,35 @@ public class MainWindow(string title)
         if (_oem.First().Epoch > time || time > _oem.Last().Epoch) return;
         
         var l = _oem.TakeWhile(line => line.Epoch <= time).Last();
-        var orb = l.AsOrbit(Program.ControlledVehicle.Parent,
-            Program.ControlledVehicle.Orbit.OrbitLineColor);
-        var dt = (time - OemLoader.KsaEpoch).TotalSeconds - Universe.GetElapsedSeconds();
+
+        // Assume the ephemeris is for the home body of the system (i.e. Earth), fall back to vehicle's current parent
+        // if null
+        var body = Universe.CurrentSystem?.HomeBody ?? Program.ControlledVehicle.Parent;
+        var orb = l.AsOrbit(body, Program.ControlledVehicle.Orbit.OrbitLineColor);
+        var simTime = new SimTime((time - OemLoader.KsaEpoch).TotalSeconds);
+
+        // If the position at the provided time is within the SOI of a child body, transform the orbit to
+        // an orbit around the child body.
+        // (Code mostly stolen from KSA.KinematicStates.CheckSoiTransitions)
+        var posCci = orb.GetStateVectorsAt(simTime).PositionCci;
+        foreach (var child in body.Children)
+        {
+            if (child is not Celestial childCelestial) continue;
+            var soi = childCelestial.SphereOfInfluence;
+            var childPos = child.GetPositionOrb(simTime).Transform(childCelestial.Orbit.GetOrb2ParentCci());
+            var distance = (posCci - childPos).Length();
+            
+            if (distance > soi) continue;
+            var rotation = doubleQuat.Concatenate(childCelestial.GetCci2Orb(), childCelestial.Orbit.Orb2ParentCci)
+                .Inverse();
+            var newPosition = (posCci - childPos).Transform(rotation);
+            var newVelocity = (orb.GetVelocityCciAt(simTime) - childCelestial.GetVelocityCci(simTime)).Transform(rotation);
+            orb = Orbit.CreateFromStateCci(childCelestial, simTime, newPosition, newVelocity, orb.OrbitLineColor);
+        }
+        
+        // Go to the specified time and set the vehicle's orbit to the ephemeris orbit at that time
+        // (this even works backwards in time, thanks to the patch in UniversePatch!)
+        var dt = simTime.Seconds() - Universe.GetElapsedSeconds();
         Universe.CompleteAndApplyPreviousOrbitSolvers();
         Universe.ResetSimulationSpeed();
         Universe.ExecuteNextOrbitSolvers(dt);
-- 
2.51.2