private static Vector <VelocityUnit> WindVector(ShotParameters shot, Wind wind, VelocityUnit units)
{
double sightCosine = shot.SightAngle.Cos();
double sightSine = shot.SightAngle.Sin();
double cantCosine = (shot.CantAngle ?? AngularUnit.Radian.New(0)).Cos();
double cantSine = (shot.CantAngle ?? AngularUnit.Radian.New(0)).Sin();
Measurement <VelocityUnit> rangeVelocity, crossComponent;
if (wind != null)
{
rangeVelocity = (wind.Velocity * wind.Direction.Cos()).To(units);
crossComponent = (wind.Velocity * wind.Direction.Sin()).To(units);
}
else
{
rangeVelocity = new Measurement <VelocityUnit>(0, units);
crossComponent = new Measurement <VelocityUnit>(0, units);
}
Measurement <VelocityUnit> rangeFactor = -rangeVelocity * sightSine;
return(new Vector <VelocityUnit>(rangeVelocity * sightCosine, rangeFactor * cantCosine + crossComponent * cantSine, crossComponent * cantCosine - rangeFactor * cantSine));
}
/// <summary>
/// Calculates the trajectory for the specified parameters.
/// </summary>
/// <param name="ammunition"></param>
/// <param name="rifle"></param>
/// <param name="atmosphere"></param>
/// <param name="shot"></param>
/// <param name="wind"></param>
/// <returns></returns>
public TrajectoryPoint[] Calculate(Ammunition ammunition, Rifle rifle, Atmosphere atmosphere, ShotParameters shot, Wind[] wind)
{
Measurement <DistanceUnit> rangeTo = shot.MaximumDistance;
Measurement <DistanceUnit> step = shot.Step;
Measurement <DistanceUnit> calculationStep = GetCalculationStep(step);
if (atmosphere == null)
{
atmosphere = new Atmosphere();
}
Measurement <DistanceUnit> alt0 = atmosphere.Altitude;
Measurement <DistanceUnit> altDelta = new Measurement <DistanceUnit>(1, DistanceUnit.Meter);
double densityFactor = 0, drag;
Measurement <VelocityUnit> mach = new Measurement <VelocityUnit>(0, VelocityUnit.MetersPerSecond);
double stabilityCoefficient = 1;
bool calculateDrift;
if (rifle.Rifling != null && ammunition.BulletDiameter != null && ammunition.BulletLength != null)
{
stabilityCoefficient = CalculateStabilityCoefficient(ammunition, rifle, atmosphere);
calculateDrift = true;
}
else
{
calculateDrift = false;
}
TrajectoryPoint[] trajectoryPoints = new TrajectoryPoint[(int)(Math.Floor(rangeTo / step)) + 1];
var barrelAzimuth = new Measurement <AngularUnit>(0.0, AngularUnit.Radian);
var barrelElevation = shot.SightAngle;
if (shot.ShotAngle != null)
{
barrelElevation += shot.ShotAngle.Value;
}
Measurement <VelocityUnit> velocity = ammunition.MuzzleVelocity;
TimeSpan time = new TimeSpan(0);
int currentWind = 0;
Measurement <DistanceUnit> nextWindRange = new Measurement <DistanceUnit>(1e7, DistanceUnit.Meter);
Vector <VelocityUnit> windVector;
if (wind == null || wind.Length < 1)
{
windVector = new Vector <VelocityUnit>();
}
else
{
if (wind.Length > 1 && wind[0].MaximumRange != null)
{
nextWindRange = wind[0].MaximumRange.Value;
}
windVector = WindVector(shot, wind[0], velocity.Unit);
}
//x - distance towards target,
//y - drop and
//z - windage
var rangeVector = new Vector <DistanceUnit>(new Measurement <DistanceUnit>(0, DistanceUnit.Meter),
-rifle.Sight.SightHeight,
new Measurement <DistanceUnit>(0, DistanceUnit.Meter));
var velocityVector = new Vector <VelocityUnit>(velocity * barrelElevation.Cos() * barrelAzimuth.Cos(),
velocity * barrelElevation.Sin(),
velocity * barrelElevation.Cos() * barrelAzimuth.Sin());
int currentItem = 0;
Measurement <DistanceUnit> maximumRange = rangeTo + calculationStep;
Measurement <DistanceUnit> nextRangeDistance = new Measurement <DistanceUnit>(0, DistanceUnit.Meter);
Measurement <DistanceUnit> lastAtAltitude = new Measurement <DistanceUnit>(-1000000, DistanceUnit.Meter);
DragTableNode dragTableNode = null;
double adjustBallisticFactorForVelocityUnits = Measurement <VelocityUnit> .Convert(1, velocity.Unit, VelocityUnit.FeetPerSecond);
double ballisicFactor = 2.08551e-04 * adjustBallisticFactorForVelocityUnits / ammunition.BallisticCoefficient.Value;
var earthGravity = (new Measurement <VelocityUnit>(Measurement <AccelerationUnit> .Convert(1, AccelerationUnit.EarthGravity, AccelerationUnit.MeterPerSecondSquare),
VelocityUnit.MetersPerSecond)).To(velocity.Unit);
//run all the way down the range
while (rangeVector.X <= maximumRange)
{
Measurement <DistanceUnit> alt = alt0 + rangeVector.Y;
//update density and Mach velocity each 10 feet of altitude
if (MeasurementMath.Abs(lastAtAltitude - alt) > altDelta)
{
atmosphere.AtAltitude(alt, out densityFactor, out mach);
lastAtAltitude = alt;
}
if (velocity < MinimumVelocity || rangeVector.Y < -MaximumDrop)
{
break;
}
if (rangeVector.X >= nextWindRange)
{
currentWind++;
windVector = WindVector(shot, wind[currentWind], velocity.Unit);
if (currentWind == wind.Length - 1 || wind[currentWind].MaximumRange == null)
{
nextWindRange = new Measurement <DistanceUnit>(1e7, DistanceUnit.Meter);
}
else
{
nextWindRange = wind[currentWind].MaximumRange.Value;
}
}
if (rangeVector.X >= nextRangeDistance)
{
var windage = rangeVector.Z;
if (calculateDrift)
{
windage += new Measurement <DistanceUnit>(1.25 * (stabilityCoefficient + 1.2) * Math.Pow(time.TotalSeconds, 1.83) * (rifle.Rifling.Direction == TwistDirection.Right ? 1 : -1), DistanceUnit.Inch);
}
trajectoryPoints[currentItem] = new TrajectoryPoint(
time: time,
weight: ammunition.Weight,
distance: rangeVector.X,
velocity: velocity,
mach: velocity / mach,
drop: rangeVector.Y,
windage: windage);
nextRangeDistance += step;
currentItem++;
if (currentItem == trajectoryPoints.Length)
{
break;
}
}
TimeSpan deltaTime = BallisticMath.TravelTime(calculationStep, velocityVector.X);
var velocityAdjusted = velocityVector - windVector;
velocity = velocityAdjusted.Magnitude;
double currentMach = velocity / mach;
//find Mach node for the first time
if (dragTableNode == null)
{
dragTableNode = DragTable.Get(ammunition.BallisticCoefficient.Table).Find(currentMach);
}
//walk towards the beginning the table as velocity drops
while (dragTableNode.Mach > currentMach)
{
dragTableNode = dragTableNode.Previous;
}
drag = ballisicFactor * densityFactor * dragTableNode.CalculateDrag(currentMach) * velocity.Value;
velocityVector = new Vector <VelocityUnit>(
velocityVector.X - deltaTime.TotalSeconds * drag * velocityAdjusted.X,
velocityVector.Y - deltaTime.TotalSeconds * drag * velocityAdjusted.Y
- earthGravity * deltaTime.TotalSeconds,
velocityVector.Z - deltaTime.TotalSeconds * drag * velocityAdjusted.Z);
var deltaRangeVector = new Vector <DistanceUnit>(calculationStep,
new Measurement <DistanceUnit>(velocityVector.Y.In(VelocityUnit.MetersPerSecond) * deltaTime.TotalSeconds, DistanceUnit.Meter),
new Measurement <DistanceUnit>(velocityVector.Z.In(VelocityUnit.MetersPerSecond) * deltaTime.TotalSeconds, DistanceUnit.Meter));
rangeVector += deltaRangeVector;
velocity = velocityVector.Magnitude;
time = time.Add(BallisticMath.TravelTime(deltaRangeVector.Magnitude, velocity));
}
return(trajectoryPoints);
}