private static double CalculateStabilityCoefficient(Ammunition ammunitionInfo, Rifle rifleInfo, Atmosphere atmosphere)
{
double weight = ammunitionInfo.Weight.In(WeightUnit.Grain);
double diameter = ammunitionInfo.BulletDiameter.Value.In(DistanceUnit.Inch);
double twist = rifleInfo.Rifling.RiflingStep.In(DistanceUnit.Inch) / diameter;
double length = ammunitionInfo.BulletLength.Value.In(DistanceUnit.Inch) / diameter;
double sd = 30 * weight / (Math.Pow(twist, 2) * Math.Pow(diameter, 3) * length * (1 + Math.Pow(length, 2)));
double fv = Math.Pow(ammunitionInfo.MuzzleVelocity.In(VelocityUnit.FeetPerSecond) / 2800, 1.0 / 3.0);
double ftp = 1;
if (atmosphere != null)
{
double ft = atmosphere.Temperature.In(TemperatureUnit.Fahrenheit);
double pt = atmosphere.Pressure.In(PressureUnit.InchesOfMercury);
ftp = ((ft + 460) / (59 + 460)) * (29.92 / pt);
}
return(sd * fv * ftp);
}
/// <summary>
/// Calculates the sight angle for the specified zero distance
/// </summary>
/// <param name="ammunition"></param>
/// <param name="rifle"></param>
/// <param name="atmosphere"></param>
/// <returns></returns>
public Measurement <AngularUnit> SightAngle(Ammunition ammunition, Rifle rifle, Atmosphere atmosphere)
{
Measurement <DistanceUnit> rangeTo = rifle.Zero.Distance * 2;
Measurement <DistanceUnit> step = rifle.Zero.Distance / 100;
Measurement <DistanceUnit> calculationStep = GetCalculationStep(step);
if (rifle.Zero.Atmosphere != null)
{
atmosphere = rifle.Zero.Atmosphere;
}
if (atmosphere == null)
{
atmosphere = new Atmosphere();
}
if (rifle.Zero.Ammunition != null)
{
ammunition = rifle.Zero.Ammunition;
}
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);
var sightAngle = new Measurement <AngularUnit>(150, AngularUnit.MOA);
var barrelAzimuth = new Measurement <AngularUnit>(0, AngularUnit.Radian);
for (int approximation = 0; approximation < 100; approximation++)
{
var barrelElevation = sightAngle;
Measurement <VelocityUnit> velocity = ammunition.MuzzleVelocity;
TimeSpan time = new TimeSpan(0);
//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());
Measurement <DistanceUnit> maximumRange = rangeTo;
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
if (MeasurementMath.Abs(lastAtAltitude - alt) > altDelta)
{
atmosphere.AtAltitude(alt, out densityFactor, out mach);
lastAtAltitude = alt;
}
if (velocity < MinimumVelocity || rangeVector.Y < -MaximumDrop)
{
break;
}
TimeSpan deltaTime = BallisticMath.TravelTime(calculationStep, velocityVector.X);
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.Previous.Mach > currentMach)
{
dragTableNode = dragTableNode.Previous;
}
drag = ballisicFactor * densityFactor * dragTableNode.CalculateDrag(currentMach) * velocity.Value;
velocityVector = new Vector <VelocityUnit>(
velocityVector.X - deltaTime.TotalSeconds * drag * velocityVector.X,
velocityVector.Y - deltaTime.TotalSeconds * drag * velocityVector.Y - earthGravity * deltaTime.TotalSeconds,
velocityVector.Z - deltaTime.TotalSeconds * drag * velocityVector.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;
if (rangeVector.X >= rifle.Zero.Distance)
{
if (Math.Abs(rangeVector.Y.In(DistanceUnit.Millimeter)) < 1)
{
return(sightAngle);
}
sightAngle += new Measurement <AngularUnit>(-rangeVector.Y.In(DistanceUnit.Centimeter) / rifle.Zero.Distance.In(DistanceUnit.Meter) * 100, AngularUnit.CmPer100Meters);
break;
}
velocity = velocityVector.Magnitude;
time = time.Add(BallisticMath.TravelTime(deltaRangeVector.Magnitude, velocity));
}
}
throw new InvalidOperationException("Cannot find zero parameters");
}
/// <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);
}