// bore = the hollow part inside a gun barrel or other tube.
// A function to generate a ballistic solution table in 1 yard increments, up to __BCOMP_MAXRANGE__.
/* Arguments:
* DragFunction: The drag function you wish to use for the solution (G1, G2, G3, G5, G6, G7, or G8)
* DragCoefficient: The coefficient of drag for the projectile you wish to model.
* Velocity: The projectile initial velocity.
* SightHeight: The height of the sighting system above the bore centerline.
* Most scopes are in the 1.5"-2.0" range.
* BoreAngle: The uphill or downhill shooting angle, in degrees. Usually 0, but can be anything from
* 90 (directly up), to -90 (directly down).
* SightToBoreAngle: The angle of the sighting system relative to the bore, in degrees. This can be easily computed
* using the CalculateSightToBoreAngle() function documented above.
* WindSpeed: The wind velocity, in mi/hr
* WindAngle: The angle at which the wind is approaching from, in degrees.
* 0 degrees is a straight headwind
* 90 degrees is from right to left
* 180 degrees is a straight tailwind
* -90 or 270 degrees is from left to right.
* Solution: A pointer provided for accessing the solution after it has been generated.
* Memory for this pointer is allocated in the function, so the user does not need
* to worry about it. This solution can be passed to the retrieval functions to get
* useful data from the solution.
* Return Value:
* This function returns an integer representing the maximum valid range of the
* solution. This also indicates the maximum number of rows in the solution matrix,
* and should not be exceeded in order to avoid a memory segmentation fault.
*/
static int SolveAll(DragFunction DragFunction, double DragCoefficient, double Velocity_feet_sec, double SightHeight_inch, double BoreAngle, double SightToBoreAngle, double WindSpeed_mile_hr, double WindAngle)
{
// seconds
double t = 0;
double dt = 0;
// feet per second
double v = 0;
double vx = 0, vx1 = 0, vy = 0, vy1 = 0;
// acceleration
double dv = 0, dvx = 0, dvy = 0;
// feet
double x = 0, y = 0;
// miles per hour
double headwind_mile_hr = HeadWindVelocity(WindSpeed_mile_hr, WindAngle);
double crosswind_mile_hr = CrossWindVelocity(WindSpeed_mile_hr, WindAngle);
// feet per second
double Gy = GRAVITY * Math.Cos(DegtoRad((BoreAngle + SightToBoreAngle)));
double Gx = GRAVITY * Math.Sin(DegtoRad((BoreAngle + SightToBoreAngle)));
vx = Velocity_feet_sec * Math.Cos(DegtoRad(SightToBoreAngle));
vy = Velocity_feet_sec * Math.Sin(DegtoRad(SightToBoreAngle));
y = -SightHeight_inch / 12;
int n = 0;
for (t = 0; ; t = t + dt)
{
// feet per second
vx1 = vx;
vy1 = vy;
v = Math.Sqrt(vx * vx + vy * vy);
// Compute acceleration using the drag function retardation.
dv = DragRetardationVelocity(DragFunction, DragCoefficient, v + headwind_mile_hr * 5280.0 / 3600.0);
dvx = -(vx / v) * dv;
dvy = -(vy / v) * dv;
// Compute velocity, including the resolved gravity vectors.
vx += dt * dvx + dt * Gx;
vy += dt * dvy + dt * Gy;
if (x / 3 >= n)
{
Projectile projectile = new Projectile();
projectile.Range = x / 3; // Range in yards
projectile.Path = y * 12; // Path in inches
projectile.MOA = -RadtoMOA(Math.Atan(y / x)); // Correction in MOA
projectile.Time = t + dt; // Time in s
projectile.Windage = WindageCorrection(crosswind_mile_hr, Velocity_feet_sec, x, t + dt); // Windage in inches
projectile.WindageMOA = RadtoMOA(Math.Atan(projectile.Windage / (12 * x))); // Windage in MOA
projectile.Velocity = v; // Velocity (combined)
projectile.Vx = vx; // Velocity (x)
projectile.Vy = vy; // Velocity (y)
ProjectileYards.Add(projectile);
n++;
}
// Compute position based on average velocity.
x += dt * (vx + vx1) / 2;
y += dt * (vy + vy1) / 2;
dt = 0.5 / v;
if (Math.Abs(vy) > Math.Abs(3 * vx))
{
break;
}
if (n >= __BCOMP_MAXRANGE__ + 1)
{
break;
}
}
size = n;
return(n);
}
// A function to calculate ballistic retardation values based on standard drag functions.
/* Arguments:
* DragFunction: G1, G2, G3, G4, G5, G6, G7, or G8. All are enumerated above.
* DragCoefficient: The coefficient of drag for the projectile for the given drag function.
* Velocity: The Velocity of the projectile.
*
* Return Value:
* The function returns the projectile drag retardation velocity, in ft/s per second.
*/
static double DragRetardationVelocity(DragFunction DragFunction, double DragCoefficient, double Velocity_feet_sec)
{
double vp = Velocity_feet_sec;
double val = -1;
double A = -1;
double M = -1;
switch (DragFunction)
{
case DragFunction.G1:
if (vp > 4230)
{
A = 1.477404177730177e-04; M = 1.9565;
}
else if (vp > 3680)
{
A = 1.920339268755614e-04; M = 1.925;
}
else if (vp > 3450)
{
A = 2.894751026819746e-04; M = 1.875;
}
else if (vp > 3295)
{
A = 4.349905111115636e-04; M = 1.825;
}
else if (vp > 3130)
{
A = 6.520421871892662e-04; M = 1.775;
}
else if (vp > 2960)
{
A = 9.748073694078696e-04; M = 1.725;
}
else if (vp > 2830)
{
A = 1.453721560187286e-03; M = 1.675;
}
else if (vp > 2680)
{
A = 2.162887202930376e-03; M = 1.625;
}
else if (vp > 2460)
{
A = 3.209559783129881e-03; M = 1.575;
}
else if (vp > 2225)
{
A = 3.904368218691249e-03; M = 1.55;
}
else if (vp > 2015)
{
A = 3.222942271262336e-03; M = 1.575;
}
else if (vp > 1890)
{
A = 2.203329542297809e-03; M = 1.625;
}
else if (vp > 1810)
{
A = 1.511001028891904e-03; M = 1.675;
}
else if (vp > 1730)
{
A = 8.609957592468259e-04; M = 1.75;
}
else if (vp > 1595)
{
A = 4.086146797305117e-04; M = 1.85;
}
else if (vp > 1520)
{
A = 1.954473210037398e-04; M = 1.95;
}
else if (vp > 1420)
{
A = 5.431896266462351e-05; M = 2.125;
}
else if (vp > 1360)
{
A = 8.847742581674416e-06; M = 2.375;
}
else if (vp > 1315)
{
A = 1.456922328720298e-06; M = 2.625;
}
else if (vp > 1280)
{
A = 2.419485191895565e-07; M = 2.875;
}
else if (vp > 1220)
{
A = 1.657956321067612e-08; M = 3.25;
}
else if (vp > 1185)
{
A = 4.745469537157371e-10; M = 3.75;
}
else if (vp > 1150)
{
A = 1.379746590025088e-11; M = 4.25;
}
else if (vp > 1100)
{
A = 4.070157961147882e-13; M = 4.75;
}
else if (vp > 1060)
{
A = 2.938236954847331e-14; M = 5.125;
}
else if (vp > 1025)
{
A = 1.228597370774746e-14; M = 5.25;
}
else if (vp > 980)
{
A = 2.916938264100495e-14; M = 5.125;
}
else if (vp > 945)
{
A = 3.855099424807451e-13; M = 4.75;
}
else if (vp > 905)
{
A = 1.185097045689854e-11; M = 4.25;
}
else if (vp > 860)
{
A = 3.566129470974951e-10; M = 3.75;
}
else if (vp > 810)
{
A = 1.045513263966272e-08; M = 3.25;
}
else if (vp > 780)
{
A = 1.291159200846216e-07; M = 2.875;
}
else if (vp > 750)
{
A = 6.824429329105383e-07; M = 2.625;
}
else if (vp > 700)
{
A = 3.569169672385163e-06; M = 2.375;
}
else if (vp > 640)
{
A = 1.839015095899579e-05; M = 2.125;
}
else if (vp > 600)
{
A = 5.71117468873424e-05; M = 1.950;
}
else if (vp > 550)
{
A = 9.226557091973427e-05; M = 1.875;
}
else if (vp > 250)
{
A = 9.337991957131389e-05; M = 1.875;
}
else if (vp > 100)
{
A = 7.225247327590413e-05; M = 1.925;
}
else if (vp > 65)
{
A = 5.792684957074546e-05; M = 1.975;
}
else if (vp > 0)
{
A = 5.206214107320588e-05; M = 2.000;
}
break;
case DragFunction.G2:
if (vp > 1674)
{
A = .0079470052136733; M = 1.36999902851493;
}
else if (vp > 1172)
{
A = 1.00419763721974e-03; M = 1.65392237010294;
}
else if (vp > 1060)
{
A = 7.15571228255369e-23; M = 7.91913562392361;
}
else if (vp > 949)
{
A = 1.39589807205091e-10; M = 3.81439537623717;
}
else if (vp > 670)
{
A = 2.34364342818625e-04; M = 1.71869536324748;
}
else if (vp > 335)
{
A = 1.77962438921838e-04; M = 1.76877550388679;
}
else if (vp > 0)
{
A = 5.18033561289704e-05; M = 1.98160270524632;
}
break;
case DragFunction.G5:
if (vp > 1730)
{
A = 7.24854775171929e-03; M = 1.41538574492812;
}
else if (vp > 1228)
{
A = 3.50563361516117e-05; M = 2.13077307854948;
}
else if (vp > 1116)
{
A = 1.84029481181151e-13; M = 4.81927320350395;
}
else if (vp > 1004)
{
A = 1.34713064017409e-22; M = 7.8100555281422;
}
else if (vp > 837)
{
A = 1.03965974081168e-07; M = 2.84204791809926;
}
else if (vp > 335)
{
A = 1.09301593869823e-04; M = 1.81096361579504;
}
else if (vp > 0)
{
A = 3.51963178524273e-05; M = 2.00477856801111;
}
break;
case DragFunction.G6:
if (vp > 3236)
{
A = 0.0455384883480781; M = 1.15997674041274;
}
else if (vp > 2065)
{
A = 7.167261849653769e-02; M = 1.10704436538885;
}
else if (vp > 1311)
{
A = 1.66676386084348e-03; M = 1.60085100195952;
}
else if (vp > 1144)
{
A = 1.01482730119215e-07; M = 2.9569674731838;
}
else if (vp > 1004)
{
A = 4.31542773103552e-18; M = 6.34106317069757;
}
else if (vp > 670)
{
A = 2.04835650496866e-05; M = 2.11688446325998;
}
else if (vp > 0)
{
A = 7.50912466084823e-05; M = 1.92031057847052;
}
break;
case DragFunction.G7:
if (vp > 4200)
{
A = 1.29081656775919e-09; M = 3.24121295355962;
}
else if (vp > 3000)
{
A = 0.0171422231434847; M = 1.27907168025204;
}
else if (vp > 1470)
{
A = 2.33355948302505e-03; M = 1.52693913274526;
}
else if (vp > 1260)
{
A = 7.97592111627665e-04; M = 1.67688974440324;
}
else if (vp > 1110)
{
A = 5.71086414289273e-12; M = 4.3212826264889;
}
else if (vp > 960)
{
A = 3.02865108244904e-17; M = 5.99074203776707;
}
else if (vp > 670)
{
A = 7.52285155782535e-06; M = 2.1738019851075;
}
else if (vp > 540)
{
A = 1.31766281225189e-05; M = 2.08774690257991;
}
else if (vp > 0)
{
A = 1.34504843776525e-05; M = 2.08702306738884;
}
break;
case DragFunction.G8:
if (vp > 3571)
{
A = .0112263766252305; M = 1.33207346655961;
}
else if (vp > 1841)
{
A = .0167252613732636; M = 1.28662041261785;
}
else if (vp > 1120)
{
A = 2.20172456619625e-03; M = 1.55636358091189;
}
else if (vp > 1088)
{
A = 2.0538037167098e-16; M = 5.80410776994789;
}
else if (vp > 976)
{
A = 5.92182174254121e-12; M = 4.29275576134191;
}
else if (vp > 0)
{
A = 4.3917343795117e-05; M = 1.99978116283334;
}
break;
default:
break;
}
if (A != -1 && M != -1 && vp > 0 && vp < 10000)
{
val = A * Math.Pow(vp, M) / DragCoefficient;
return(val);
}
else
{
return(-1);
}
}
// bore = the hollow part inside a gun barrel or other tube.
// A function to determine the bore angle needed to achieve a target zero at Range yards
// (at standard conditions and on level ground.)
/* Arguments:
* DragFunction: The drag function to use (G1, G2, G3, G5, G6, G7, G8)
* DragCoefficient: The coefficient of drag for the projectile, for the supplied drag function.
* Velocity: The initial velocity of the projectile, in feet/s
* SightHeight: The height of the sighting system above the bore centerline, in inches.
* Most scopes fall in the 1.6 to 2.0 inch range.
* ZeroRange: The range in yards, at which you wish the projectile to intersect yIntercept.
* yIntercept: The height, in inches, you wish for the projectile to be when it crosses ZeroRange yards.
* This is usually 0 for a target zero, but could be any number. For example if you wish
* to sight your rifle in 1.5" high at 100 yards, then you would set yIntercept to 1.5, and ZeroRange to 100
*
* Return Value:
* Returns the angle of the bore relative to the sighting system, in degrees.
*/
static double CalculateSightToBoreAngle(DragFunction DragFunction, double DragCoefficient, double Velocity_feet_sec, double SightHeight_inch, double ZeroRange_yard, double yIntercept_inch)
{
// Numerical Integration variables
double t = 0;
double dt = 1 / Velocity_feet_sec; // The solution accuracy generally doesn't suffer if its within a foot for each second of time.
double y = 0; /*-SightHeight/12;*/
double x = 0;
double da; // The change in the bore angle used to iterate in on the correct zero angle.
// State variables for each integration loop.
double v = 0, vx = 0, vy = 0; // velocity
double vx1 = 0, vy1 = 0; // Last frame's velocity, used for computing average velocity.
double dv = 0, dvx = 0, dvy = 0; // acceleration
double Gx = 0, Gy = 0; // Gravitational acceleration
double angle = 0; // The actual angle of the bore.
// Start with a very coarse angular change, to quickly solve even large launch angle problems.
da = DegtoRad(14);
// The general idea here is to start at 0 degrees elevation, and increase the elevation by 14 degrees
// until we are above the correct elevation. Then reduce the angular change by half, and begin reducing
// the angle. Once we are again below the correct angle, reduce the angular change by half again, and go
// back up. This allows for a fast successive approximation of the correct elevation, usually within less
// than 20 iterations.
for (angle = 0; ; angle = angle + da)
{
vy = Velocity_feet_sec * Math.Sin(angle);
vx = Velocity_feet_sec * Math.Cos(angle);
Gx = GRAVITY * Math.Sin(angle);
Gy = GRAVITY * Math.Cos(angle);
for (t = 0, x = 0, y = 0 - SightHeight_inch / 12; x <= ZeroRange_yard * 3; t = t + dt)
{
vy1 = vy;
vx1 = vx;
v = Math.Sqrt(vx * vx + vy * vy);
dt = 1 / v;
// Compute acceleration using the drag function retardation.
dv = DragRetardationVelocity(DragFunction, DragCoefficient, v);
dvx = -(vx / v) * dv;
dvy = -(vy / v) * dv;
// Compute velocity, including the resolved gravity vectors.
vx += dt * dvx + dt * Gx;
vy += dt * dvy + dt * Gy;
x += dt * (vx + vx1) / 2;
y += dt * (vy + vy1) / 2;
// Break early to save CPU time if we won't find a solution.
if (vy < 0 && y < yIntercept_inch)
{
break;
}
if (vy > 3 * vx)
{
break;
}
}
if (y > yIntercept_inch && da > 0)
{
da = -da / 2;
}
if (y < yIntercept_inch && da < 0)
{
da = -da / 2;
}
if (Math.Abs(da) < MOAtoRad(0.01))
{
break; // If our accuracy is sufficient, we can stop approximating.
}
if (angle > DegtoRad(45))
{
break; // If we exceed the 45 degree launch angle, then the projectile just won't get there, so we stop trying.
}
}
return(RadtoDeg(angle)); // Convert to degrees for return value.
}
