/// <summary>
/// Traces a space craft orbit by re-centering the world around the parent.
/// </summary>
public static void TraceSpaceCraft(SpaceCraftBase satellite, OrbitTrace trace)
{
IMassiveBody parent = satellite.GravitationalParent;
DVector2 initialPosition = satellite.Position - parent.Position;
var shipOffset = new DVector2(Math.Cos(satellite.Pitch) * (satellite.TotalWidth - satellite.Width),
Math.Sin(satellite.Pitch) * (satellite.TotalHeight - satellite.Height)) * 0.5;
initialPosition -= shipOffset;
var proxyParent = new MassiveBodyProxy(DVector2.Zero, DVector2.Zero, parent);
var proxySatellite = new SpaceCraftProxy(initialPosition, satellite.Velocity - parent.Velocity, satellite);
proxySatellite.SetGravitationalParent(proxyParent);
int stepCount;
double targetDt;
double proximityDt;
double orbitalDt = 0;
bool isOrbiting;
double altitude = proxyParent.GetRelativeHeight(proxySatellite.Position);
double proximityAltitude = proxyParent.SurfaceRadius * 0.15;
if (altitude < proximityAltitude)
{
stepCount = 1100;
isOrbiting = false;
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = proximityDt;
}
else
{
stepCount = 600;
isOrbiting = true;
orbitalDt = GetOrbitalDt(initialPosition.Length(), parent.Mass, proxySatellite.Velocity.Length());
targetDt = orbitalDt;
}
// Assumes that the parent is (0,0) which will be true in this case
double previousAngle = proxySatellite.Position.Angle();
double totalAngularDisplacement = 0;
trace.Reset(satellite.Position - shipOffset);
// Update steps based on orbit vs atmosphere
for (int step = 0; step < stepCount; step++)
{
proxySatellite.ResetAccelerations();
proxySatellite.ResolveGravitation(proxyParent);
proxySatellite.ResolveAtmopsherics(proxyParent);
proxySatellite.Update(targetDt);
double currentAngle = proxySatellite.Position.Angle();
totalAngularDisplacement += DeltaAngle(currentAngle, previousAngle);
// Made a full orbit
if (totalAngularDisplacement > AngularCutoff)
{
break;
}
previousAngle = currentAngle;
altitude = proxyParent.GetRelativeHeight(proxySatellite.Position);
double velocity = proxySatellite.GetRelativeVelocity().Length();
double offsetFactor = 0.0;
//if (altitude < proxyParent.AtmosphereHeight*2)
if (altitude < proxyParent.AtmosphereHeight * 4)
{
if (velocity < 3000)
{
offsetFactor = 1.0;
}
else if (velocity < 4000)
{
offsetFactor = 1.0 - velocity / 3000.0;
}
}
// Check if reference frame shifting needs to occur in atmosphere
if (offsetFactor > 0.0001)
{
DVector2 difference = proxyParent.Position - proxySatellite.Position;
difference.Normalize();
var surfaceNormal = new DVector2(-difference.Y, difference.X);
double altitudeFromCenter = altitude + proxyParent.SurfaceRadius;
// Distance of circumference at this altitude ( c= r * 2pi )
double pathCirumference = Constants.TwoPi * altitudeFromCenter;
double rotationalSpeed = pathCirumference / parent.RotationPeriod;
DVector2 atmopshereVelocity = surfaceNormal * rotationalSpeed;
proxySatellite.ApplyFrameOffset(atmopshereVelocity * offsetFactor * targetDt);
}
// Return early if the trace goes into a planet
if (altitude <= 0)
{
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
break;
}
// Determine the correct change overs from orbital to surface proximity
if (isOrbiting)
{
if (altitude < proximityAltitude)
{
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = MathHelper.Lerp(targetDt, proximityDt, 0.75);
isOrbiting = false;
stepCount = 1000;
}
else
{
targetDt = MathHelper.Lerp(targetDt, orbitalDt, 0.1);
}
}
else
{
if (altitude > proximityAltitude)
{
orbitalDt = GetOrbitalDt(proxySatellite.Position.Length(), parent.Mass, proxySatellite.Velocity.Length());
targetDt = MathHelper.Lerp(targetDt, orbitalDt, 0.1);
isOrbiting = true;
stepCount = 600;
}
else
{
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = MathHelper.Lerp(targetDt, proximityDt, 0.75);
}
}
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
}
}
/// <summary>
/// Traces a space craft orbit by re-centering the world around the parent.
/// </summary>
public static void TraceSpaceCraft(SpaceCraftBase satellite, OrbitTrace trace)
{
IMassiveBody parent = satellite.GravitationalParent;
DVector2 initialPosition = satellite.Position - parent.Position;
var shipOffset = new DVector2(Math.Cos(satellite.Pitch) * (satellite.TotalWidth - satellite.Width),
Math.Sin(satellite.Pitch) * (satellite.TotalHeight - satellite.Height)) * 0.5;
initialPosition -= shipOffset;
var proxyParent = new MassiveBodyProxy(DVector2.Zero, DVector2.Zero, parent);
var proxySatellite = new SpaceCraftProxy(initialPosition, satellite.Velocity - parent.Velocity, satellite);
proxySatellite.SetGravitationalParent(proxyParent);
int stepCount;
double targetDt;
double proximityDt;
double orbitalDt = 0;
bool isOrbiting;
double orbitalTerminationRadius = 0;
double altitude = proxyParent.GetRelativeHeight(proxySatellite.Position);
double proximityAltitude = proxyParent.SurfaceRadius * 0.15;
if (altitude < proximityAltitude)
{
stepCount = 1100;
isOrbiting = false;
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = proximityDt;
}
else
{
stepCount = 600;
isOrbiting = true;
orbitalDt = GetOrbitalDt(initialPosition, proxySatellite.Velocity, out orbitalTerminationRadius);
targetDt = orbitalDt;
}
trace.Reset(satellite.Position - shipOffset);
// Simulate 300 orbital steps, more for proximity
for (int step = 0; step < stepCount; step++)
{
proxySatellite.ResetAccelerations();
proxySatellite.ResolveGravitation(proxyParent);
proxySatellite.ResolveAtmopsherics(proxyParent);
proxySatellite.Update(targetDt);
altitude = proxyParent.GetRelativeHeight(proxySatellite.Position);
double velocity = proxySatellite.GetRelativeVelocity().Length();
double offsetFactor = 0.0;
if (altitude < proxyParent.AtmosphereHeight * 2)
{
if (velocity < 3000)
{
offsetFactor = 1.0;
}
else if (velocity < 4000)
{
offsetFactor = 1.0 - velocity / 3000.0;
}
}
// Check if reference frame shifting needs to occur in atmosphere
if (offsetFactor > 0.0001)
{
DVector2 difference = proxyParent.Position - proxySatellite.Position;
difference.Normalize();
var surfaceNormal = new DVector2(-difference.Y, difference.X);
double altitudeFromCenter = altitude + proxyParent.SurfaceRadius;
// Distance of circumference at this altitude ( c= 2r * pi )
double pathCirumference = 2 * Math.PI * altitudeFromCenter;
double rotationalSpeed = pathCirumference / parent.RotationPeriod;
DVector2 atmopshereVelocity = surfaceNormal * rotationalSpeed;
proxySatellite.ApplyFrameOffset(atmopshereVelocity * offsetFactor * targetDt);
// Return early if the trace goes into a planet
if (altitude <= 0)
{
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
break;
}
}
// Determine the correct change overs from orbital to surface proximity
if (isOrbiting)
{
if (altitude < proximityAltitude)
{
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = MathHelper.Lerp(targetDt, proximityDt, 0.75);
isOrbiting = false;
stepCount = 1000;
}
else
{
targetDt = MathHelper.Lerp(targetDt, orbitalDt, 0.1);
}
}
else
{
if (altitude > proximityAltitude)
{
orbitalDt = GetOrbitalDt(proxySatellite.Position, proxySatellite.Velocity, out orbitalTerminationRadius);
targetDt = MathHelper.Lerp(targetDt, orbitalDt, 0.1);
isOrbiting = true;
stepCount = 600;
}
else
{
proximityDt = GetProximityDt(altitude, proximityAltitude);
targetDt = MathHelper.Lerp(targetDt, proximityDt, 0.75);
}
}
// Check expensive termination conditions after half of the iterations
if (isOrbiting && step > 100)
{
DVector2 offsetVector = proxySatellite.Position - initialPosition;
double distanceFromStart = offsetVector.Length();
// Terminate and add the end point
if (distanceFromStart < orbitalTerminationRadius)
{
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
break;
}
}
trace.AddPoint(proxySatellite.Position + parent.Position, altitude);
}
}