Drag.go

package externalballistics

import (
	"fmt"
	"math"
)

//DragTableG1 is identifier for G1 ballistic table
const DragTableG1 byte = 1

//DragTableG2 is identifier for G2 ballistic table
const DragTableG2 byte = 2

//DragTableG5 is identifier for G5 ballistic table
const DragTableG5 byte = 3

//DragTableG6 is identifier for G6 ballistic table
const DragTableG6 byte = 4

//DragTableG7 is identifier for G7 ballistic table
const DragTableG7 byte = 5

//DragTableG8 is identifier for G8 ballistic table
const DragTableG8 byte = 6

//DragTableGS is identifier for GL ballistic table
const DragTableGS byte = 7

//DragTableGC for a custom drag table
const DragTableGC byte = 8

type dragFunction func(float64) float64

//
//BallisticCoefficient keeps data about ballistic coefficient
//of a projectile
//
//The ballistic coefficient (BC) of a body is a measure of its
//ability to overcome air resistance in flight.
//
//The small arm ballistics, BC is expressed vs
//a standard projectile. Different ballistic tables
//uses different standard projectiles, for example G1 uses
//flat based 2 caliber length with a 2 caliber ogive
//
//G1 and G7 are the most used for small arms ballistics
//
type BallisticCoefficient struct {
	// value is the ballistic coefficient
	value float64
	// type of the value: BC or FF
	valueType byte
	// the identifier of the ballistic table
	table byte
	// the drag function
	drag dragFunction
}

//
//BC is the type of the ballisic coefficient value: Ballicitic Coefficient
//
const BC = 1

//
//FF is the type of the ballisic coefficient value: Form Factor
//
const FF = 2

func dragFunctionFactory(dragTable byte) dragFunction {
	switch dragTable {
	case DragTableG1:
		return func(mach float64) float64 {
			return CalculateByCurve(g1Table, g1Curve, mach)
		}
	case DragTableG2:
		return func(mach float64) float64 {
			return CalculateByCurve(g2Table, g2Curve, mach)
		}
	case DragTableG5:
		return func(mach float64) float64 {
			return CalculateByCurve(g5Table, g5Curve, mach)
		}
	case DragTableG6:
		return func(mach float64) float64 {
			return CalculateByCurve(g6Table, g6Curve, mach)
		}
	case DragTableG7:
		return func(mach float64) float64 {
			return CalculateByCurve(g7Table, g7Curve, mach)
		}
	case DragTableG8:
		return func(mach float64) float64 {
			return CalculateByCurve(g8Table, g8Curve, mach)
		}
	case DragTableGS:
		return func(mach float64) float64 {
			return CalculateByCurve(gSTable, gSCurve, mach)
		}
	default:
		panic(fmt.Errorf("unknown drag table type"))
	}
}

//CreateBallisticCoefficient creates ballistic coefficient object using the
//the custom drag function
func CreateBallisticCoefficientForCustomDragFunction(value float64, valueType byte, dragTable dragFunction) (BallisticCoefficient, error) {
	if value <= 0 {
		return BallisticCoefficient{}, fmt.Errorf("BallisticCoefficient: Drag coefficient must be greater than zero")
	}
	if valueType != BC && valueType != FF {
		return BallisticCoefficient{}, fmt.Errorf("BallisticCoefficient: The value type must be either BC or FF")
	}
	return BallisticCoefficient{
		value:     value,
		valueType: valueType,
		table:     DragTableGC,
		drag:      dragTable,
	}, nil
}

//CreateBallisticCoefficient creates ballistic coefficient object using the
//ballistic coefficient value and ballistic table.
func CreateBallisticCoefficient(value float64, dragTable byte) (BallisticCoefficient, error) {
	if dragTable < DragTableG1 || DragTableG1 > DragTableGS {
		return BallisticCoefficient{}, fmt.Errorf("BallisticCoefficient: Unknown drag table %d", dragTable)
	}
	if value <= 0 {
		return BallisticCoefficient{}, fmt.Errorf("BallisticCoefficient: Drag coefficient must be greater than zero")
	}
	return BallisticCoefficient{
		value:     value,
		valueType: BC,
		table:     dragTable,
		drag:      dragFunctionFactory(dragTable),
	}, nil
}

//Value returns the ballistic coefficient value
func (v BallisticCoefficient) Value() float64 {
	return v.value
}

//ValueType returns the ballistic coefficient value type (BC or FF)
func (v BallisticCoefficient) ValueType() byte {
	return v.valueType
}

//Table return the name of the ballistic table
func (v BallisticCoefficient) Table() byte {
	return v.table
}

//PIR = (PI/8)*(RHO0/144)
const PIR = 2.08551e-04

//Drag calculates the aerodynamic drag (deceleration factor) calculated for the speed
//expressed in mach (speed of sound)
func (v BallisticCoefficient) Drag(mach float64) float64 {
	return v.drag(mach) * PIR
}

//DataPoint is one value of the ballistic table used in
//table-based calculations below
//
//The calculation is based on original JavaScript code
//by Alexandre Trofimov
type DataPoint struct {
	A, B float64
}

//CurvePoint is an approximation of drag to speed function curve made on the
//base of the ballistic
type CurvePoint struct {
	A, B, C float64
}

var g1Table = []DataPoint{
	{A: 0.00, B: 0.2629},
	{A: 0.05, B: 0.2558},
	{A: 0.10, B: 0.2487},
	{A: 0.15, B: 0.2413},
	{A: 0.20, B: 0.2344},
	{A: 0.25, B: 0.2278},
	{A: 0.30, B: 0.2214},
	{A: 0.35, B: 0.2155},
	{A: 0.40, B: 0.2104},
	{A: 0.45, B: 0.2061},
	{A: 0.50, B: 0.2032},
	{A: 0.55, B: 0.2020},
	{A: 0.60, B: 0.2034},
	{A: 0.70, B: 0.2165},
	{A: 0.725, B: 0.2230},
	{A: 0.75, B: 0.2313},
	{A: 0.775, B: 0.2417},
	{A: 0.80, B: 0.2546},
	{A: 0.825, B: 0.2706},
	{A: 0.85, B: 0.2901},
	{A: 0.875, B: 0.3136},
	{A: 0.90, B: 0.3415},
	{A: 0.925, B: 0.3734},
	{A: 0.95, B: 0.4084},
	{A: 0.975, B: 0.4448},
	{A: 1.0, B: 0.4805},
	{A: 1.025, B: 0.5136},
	{A: 1.05, B: 0.5427},
	{A: 1.075, B: 0.5677},
	{A: 1.10, B: 0.5883},
	{A: 1.125, B: 0.6053},
	{A: 1.15, B: 0.6191},
	{A: 1.20, B: 0.6393},
	{A: 1.25, B: 0.6518},
	{A: 1.30, B: 0.6589},
	{A: 1.35, B: 0.6621},
	{A: 1.40, B: 0.6625},
	{A: 1.45, B: 0.6607},
	{A: 1.50, B: 0.6573},
	{A: 1.55, B: 0.6528},
	{A: 1.60, B: 0.6474},
	{A: 1.65, B: 0.6413},
	{A: 1.70, B: 0.6347},
	{A: 1.75, B: 0.6280},
	{A: 1.80, B: 0.6210},
	{A: 1.85, B: 0.6141},
	{A: 1.90, B: 0.6072},
	{A: 1.95, B: 0.6003},
	{A: 2.00, B: 0.5934},
	{A: 2.05, B: 0.5867},
	{A: 2.10, B: 0.5804},
	{A: 2.15, B: 0.5743},
	{A: 2.20, B: 0.5685},
	{A: 2.25, B: 0.5630},
	{A: 2.30, B: 0.5577},
	{A: 2.35, B: 0.5527},
	{A: 2.40, B: 0.5481},
	{A: 2.45, B: 0.5438},
	{A: 2.50, B: 0.5397},
	{A: 2.60, B: 0.5325},
	{A: 2.70, B: 0.5264},
	{A: 2.80, B: 0.5211},
	{A: 2.90, B: 0.5168},
	{A: 3.00, B: 0.5133},
	{A: 3.10, B: 0.5105},
	{A: 3.20, B: 0.5084},
	{A: 3.30, B: 0.5067},
	{A: 3.40, B: 0.5054},
	{A: 3.50, B: 0.5040},
	{A: 3.60, B: 0.5030},
	{A: 3.70, B: 0.5022},
	{A: 3.80, B: 0.5016},
	{A: 3.90, B: 0.5010},
	{A: 4.00, B: 0.5006},
	{A: 4.20, B: 0.4998},
	{A: 4.40, B: 0.4995},
	{A: 4.60, B: 0.4992},
	{A: 4.80, B: 0.4990},
	{A: 5.00, B: 0.4988},
}

var g1Curve = CalculateCurve(g1Table)

var g7Table = []DataPoint{
	{A: 0.00, B: 0.1198},
	{A: 0.05, B: 0.1197},
	{A: 0.10, B: 0.1196},
	{A: 0.15, B: 0.1194},
	{A: 0.20, B: 0.1193},
	{A: 0.25, B: 0.1194},
	{A: 0.30, B: 0.1194},
	{A: 0.35, B: 0.1194},
	{A: 0.40, B: 0.1193},
	{A: 0.45, B: 0.1193},
	{A: 0.50, B: 0.1194},
	{A: 0.55, B: 0.1193},
	{A: 0.60, B: 0.1194},
	{A: 0.65, B: 0.1197},
	{A: 0.70, B: 0.1202},
	{A: 0.725, B: 0.1207},
	{A: 0.75, B: 0.1215},
	{A: 0.775, B: 0.1226},
	{A: 0.80, B: 0.1242},
	{A: 0.825, B: 0.1266},
	{A: 0.85, B: 0.1306},
	{A: 0.875, B: 0.1368},
	{A: 0.90, B: 0.1464},
	{A: 0.925, B: 0.1660},
	{A: 0.95, B: 0.2054},
	{A: 0.975, B: 0.2993},
	{A: 1.0, B: 0.3803},
	{A: 1.025, B: 0.4015},
	{A: 1.05, B: 0.4043},
	{A: 1.075, B: 0.4034},
	{A: 1.10, B: 0.4014},
	{A: 1.125, B: 0.3987},
	{A: 1.15, B: 0.3955},
	{A: 1.20, B: 0.3884},
	{A: 1.25, B: 0.3810},
	{A: 1.30, B: 0.3732},
	{A: 1.35, B: 0.3657},
	{A: 1.40, B: 0.3580},
	{A: 1.50, B: 0.3440},
	{A: 1.55, B: 0.3376},
	{A: 1.60, B: 0.3315},
	{A: 1.65, B: 0.3260},
	{A: 1.70, B: 0.3209},
	{A: 1.75, B: 0.3160},
	{A: 1.80, B: 0.3117},
	{A: 1.85, B: 0.3078},
	{A: 1.90, B: 0.3042},
	{A: 1.95, B: 0.3010},
	{A: 2.00, B: 0.2980},
	{A: 2.05, B: 0.2951},
	{A: 2.10, B: 0.2922},
	{A: 2.15, B: 0.2892},
	{A: 2.20, B: 0.2864},
	{A: 2.25, B: 0.2835},
	{A: 2.30, B: 0.2807},
	{A: 2.35, B: 0.2779},
	{A: 2.40, B: 0.2752},
	{A: 2.45, B: 0.2725},
	{A: 2.50, B: 0.2697},
	{A: 2.55, B: 0.2670},
	{A: 2.60, B: 0.2643},
	{A: 2.65, B: 0.2615},
	{A: 2.70, B: 0.2588},
	{A: 2.75, B: 0.2561},
	{A: 2.80, B: 0.2533},
	{A: 2.85, B: 0.2506},
	{A: 2.90, B: 0.2479},
	{A: 2.95, B: 0.2451},
	{A: 3.00, B: 0.2424},
	{A: 3.10, B: 0.2368},
	{A: 3.20, B: 0.2313},
	{A: 3.30, B: 0.2258},
	{A: 3.40, B: 0.2205},
	{A: 3.50, B: 0.2154},
	{A: 3.60, B: 0.2106},
	{A: 3.70, B: 0.2060},
	{A: 3.80, B: 0.2017},
	{A: 3.90, B: 0.1975},
	{A: 4.00, B: 0.1935},
	{A: 4.20, B: 0.1861},
	{A: 4.40, B: 0.1793},
	{A: 4.60, B: 0.1730},
	{A: 4.80, B: 0.1672},
	{A: 5.00, B: 0.1618},
}

var g7Curve = CalculateCurve(g7Table)

var g2Table = []DataPoint{
	{A: 0.00, B: 0.2303},
	{A: 0.05, B: 0.2298},
	{A: 0.10, B: 0.2287},
	{A: 0.15, B: 0.2271},
	{A: 0.20, B: 0.2251},
	{A: 0.25, B: 0.2227},
	{A: 0.30, B: 0.2196},
	{A: 0.35, B: 0.2156},
	{A: 0.40, B: 0.2107},
	{A: 0.45, B: 0.2048},
	{A: 0.50, B: 0.1980},
	{A: 0.55, B: 0.1905},
	{A: 0.60, B: 0.1828},
	{A: 0.65, B: 0.1758},
	{A: 0.70, B: 0.1702},
	{A: 0.75, B: 0.1669},
	{A: 0.775, B: 0.1664},
	{A: 0.80, B: 0.1667},
	{A: 0.825, B: 0.1682},
	{A: 0.85, B: 0.1711},
	{A: 0.875, B: 0.1761},
	{A: 0.90, B: 0.1831},
	{A: 0.925, B: 0.2004},
	{A: 0.95, B: 0.2589},
	{A: 0.975, B: 0.3492},
	{A: 1.0, B: 0.3983},
	{A: 1.025, B: 0.4075},
	{A: 1.05, B: 0.4103},
	{A: 1.075, B: 0.4114},
	{A: 1.10, B: 0.4106},
	{A: 1.125, B: 0.4089},
	{A: 1.15, B: 0.4068},
	{A: 1.175, B: 0.4046},
	{A: 1.20, B: 0.4021},
	{A: 1.25, B: 0.3966},
	{A: 1.30, B: 0.3904},
	{A: 1.35, B: 0.3835},
	{A: 1.40, B: 0.3759},
	{A: 1.45, B: 0.3678},
	{A: 1.50, B: 0.3594},
	{A: 1.55, B: 0.3512},
	{A: 1.60, B: 0.3432},
	{A: 1.65, B: 0.3356},
	{A: 1.70, B: 0.3282},
	{A: 1.75, B: 0.3213},
	{A: 1.80, B: 0.3149},
	{A: 1.85, B: 0.3089},
	{A: 1.90, B: 0.3033},
	{A: 1.95, B: 0.2982},
	{A: 2.00, B: 0.2933},
	{A: 2.05, B: 0.2889},
	{A: 2.10, B: 0.2846},
	{A: 2.15, B: 0.2806},
	{A: 2.20, B: 0.2768},
	{A: 2.25, B: 0.2731},
	{A: 2.30, B: 0.2696},
	{A: 2.35, B: 0.2663},
	{A: 2.40, B: 0.2632},
	{A: 2.45, B: 0.2602},
	{A: 2.50, B: 0.2572},
	{A: 2.55, B: 0.2543},
	{A: 2.60, B: 0.2515},
	{A: 2.65, B: 0.2487},
	{A: 2.70, B: 0.2460},
	{A: 2.75, B: 0.2433},
	{A: 2.80, B: 0.2408},
	{A: 2.85, B: 0.2382},
	{A: 2.90, B: 0.2357},
	{A: 2.95, B: 0.2333},
	{A: 3.00, B: 0.2309},
	{A: 3.10, B: 0.2262},
	{A: 3.20, B: 0.2217},
	{A: 3.30, B: 0.2173},
	{A: 3.40, B: 0.2132},
	{A: 3.50, B: 0.2091},
	{A: 3.60, B: 0.2052},
	{A: 3.70, B: 0.2014},
	{A: 3.80, B: 0.1978},
	{A: 3.90, B: 0.1944},
	{A: 4.00, B: 0.1912},
	{A: 4.20, B: 0.1851},
	{A: 4.40, B: 0.1794},
	{A: 4.60, B: 0.1741},
	{A: 4.80, B: 0.1693},
	{A: 5.00, B: 0.1648},
}

var g2Curve = CalculateCurve(g2Table)

var g5Table = []DataPoint{
	{A: 0.00, B: 0.1710},
	{A: 0.05, B: 0.1719},
	{A: 0.10, B: 0.1727},
	{A: 0.15, B: 0.1732},
	{A: 0.20, B: 0.1734},
	{A: 0.25, B: 0.1730},
	{A: 0.30, B: 0.1718},
	{A: 0.35, B: 0.1696},
	{A: 0.40, B: 0.1668},
	{A: 0.45, B: 0.1637},
	{A: 0.50, B: 0.1603},
	{A: 0.55, B: 0.1566},
	{A: 0.60, B: 0.1529},
	{A: 0.65, B: 0.1497},
	{A: 0.70, B: 0.1473},
	{A: 0.75, B: 0.1463},
	{A: 0.80, B: 0.1489},
	{A: 0.85, B: 0.1583},
	{A: 0.875, B: 0.1672},
	{A: 0.90, B: 0.1815},
	{A: 0.925, B: 0.2051},
	{A: 0.95, B: 0.2413},
	{A: 0.975, B: 0.2884},
	{A: 1.0, B: 0.3379},
	{A: 1.025, B: 0.3785},
	{A: 1.05, B: 0.4032},
	{A: 1.075, B: 0.4147},
	{A: 1.10, B: 0.4201},
	{A: 1.15, B: 0.4278},
	{A: 1.20, B: 0.4338},
	{A: 1.25, B: 0.4373},
	{A: 1.30, B: 0.4392},
	{A: 1.35, B: 0.4403},
	{A: 1.40, B: 0.4406},
	{A: 1.45, B: 0.4401},
	{A: 1.50, B: 0.4386},
	{A: 1.55, B: 0.4362},
	{A: 1.60, B: 0.4328},
	{A: 1.65, B: 0.4286},
	{A: 1.70, B: 0.4237},
	{A: 1.75, B: 0.4182},
	{A: 1.80, B: 0.4121},
	{A: 1.85, B: 0.4057},
	{A: 1.90, B: 0.3991},
	{A: 1.95, B: 0.3926},
	{A: 2.00, B: 0.3861},
	{A: 2.05, B: 0.3800},
	{A: 2.10, B: 0.3741},
	{A: 2.15, B: 0.3684},
	{A: 2.20, B: 0.3630},
	{A: 2.25, B: 0.3578},
	{A: 2.30, B: 0.3529},
	{A: 2.35, B: 0.3481},
	{A: 2.40, B: 0.3435},
	{A: 2.45, B: 0.3391},
	{A: 2.50, B: 0.3349},
	{A: 2.60, B: 0.3269},
	{A: 2.70, B: 0.3194},
	{A: 2.80, B: 0.3125},
	{A: 2.90, B: 0.3060},
	{A: 3.00, B: 0.2999},
	{A: 3.10, B: 0.2942},
	{A: 3.20, B: 0.2889},
	{A: 3.30, B: 0.2838},
	{A: 3.40, B: 0.2790},
	{A: 3.50, B: 0.2745},
	{A: 3.60, B: 0.2703},
	{A: 3.70, B: 0.2662},
	{A: 3.80, B: 0.2624},
	{A: 3.90, B: 0.2588},
	{A: 4.00, B: 0.2553},
	{A: 4.20, B: 0.2488},
	{A: 4.40, B: 0.2429},
	{A: 4.60, B: 0.2376},
	{A: 4.80, B: 0.2326},
	{A: 5.00, B: 0.2280},
}

var g5Curve = CalculateCurve(g5Table)

var g6Table = []DataPoint{
	{A: 0.00, B: 0.2617},
	{A: 0.05, B: 0.2553},
	{A: 0.10, B: 0.2491},
	{A: 0.15, B: 0.2432},
	{A: 0.20, B: 0.2376},
	{A: 0.25, B: 0.2324},
	{A: 0.30, B: 0.2278},
	{A: 0.35, B: 0.2238},
	{A: 0.40, B: 0.2205},
	{A: 0.45, B: 0.2177},
	{A: 0.50, B: 0.2155},
	{A: 0.55, B: 0.2138},
	{A: 0.60, B: 0.2126},
	{A: 0.65, B: 0.2121},
	{A: 0.70, B: 0.2122},
	{A: 0.75, B: 0.2132},
	{A: 0.80, B: 0.2154},
	{A: 0.85, B: 0.2194},
	{A: 0.875, B: 0.2229},
	{A: 0.90, B: 0.2297},
	{A: 0.925, B: 0.2449},
	{A: 0.95, B: 0.2732},
	{A: 0.975, B: 0.3141},
	{A: 1.0, B: 0.3597},
	{A: 1.025, B: 0.3994},
	{A: 1.05, B: 0.4261},
	{A: 1.075, B: 0.4402},
	{A: 1.10, B: 0.4465},
	{A: 1.125, B: 0.4490},
	{A: 1.15, B: 0.4497},
	{A: 1.175, B: 0.4494},
	{A: 1.20, B: 0.4482},
	{A: 1.225, B: 0.4464},
	{A: 1.25, B: 0.4441},
	{A: 1.30, B: 0.4390},
	{A: 1.35, B: 0.4336},
	{A: 1.40, B: 0.4279},
	{A: 1.45, B: 0.4221},
	{A: 1.50, B: 0.4162},
	{A: 1.55, B: 0.4102},
	{A: 1.60, B: 0.4042},
	{A: 1.65, B: 0.3981},
	{A: 1.70, B: 0.3919},
	{A: 1.75, B: 0.3855},
	{A: 1.80, B: 0.3788},
	{A: 1.85, B: 0.3721},
	{A: 1.90, B: 0.3652},
	{A: 1.95, B: 0.3583},
	{A: 2.00, B: 0.3515},
	{A: 2.05, B: 0.3447},
	{A: 2.10, B: 0.3381},
	{A: 2.15, B: 0.3314},
	{A: 2.20, B: 0.3249},
	{A: 2.25, B: 0.3185},
	{A: 2.30, B: 0.3122},
	{A: 2.35, B: 0.3060},
	{A: 2.40, B: 0.3000},
	{A: 2.45, B: 0.2941},
	{A: 2.50, B: 0.2883},
	{A: 2.60, B: 0.2772},
	{A: 2.70, B: 0.2668},
	{A: 2.80, B: 0.2574},
	{A: 2.90, B: 0.2487},
	{A: 3.00, B: 0.2407},
	{A: 3.10, B: 0.2333},
	{A: 3.20, B: 0.2265},
	{A: 3.30, B: 0.2202},
	{A: 3.40, B: 0.2144},
	{A: 3.50, B: 0.2089},
	{A: 3.60, B: 0.2039},
	{A: 3.70, B: 0.1991},
	{A: 3.80, B: 0.1947},
	{A: 3.90, B: 0.1905},
	{A: 4.00, B: 0.1866},
	{A: 4.20, B: 0.1794},
	{A: 4.40, B: 0.1730},
	{A: 4.60, B: 0.1673},
	{A: 4.80, B: 0.1621},
	{A: 5.00, B: 0.1574},
}

var g6Curve = CalculateCurve(g6Table)

var g8Table = []DataPoint{
	{A: 0.00, B: 0.2105},
	{A: 0.05, B: 0.2105},
	{A: 0.10, B: 0.2104},
	{A: 0.15, B: 0.2104},
	{A: 0.20, B: 0.2103},
	{A: 0.25, B: 0.2103},
	{A: 0.30, B: 0.2103},
	{A: 0.35, B: 0.2103},
	{A: 0.40, B: 0.2103},
	{A: 0.45, B: 0.2102},
	{A: 0.50, B: 0.2102},
	{A: 0.55, B: 0.2102},
	{A: 0.60, B: 0.2102},
	{A: 0.65, B: 0.2102},
	{A: 0.70, B: 0.2103},
	{A: 0.75, B: 0.2103},
	{A: 0.80, B: 0.2104},
	{A: 0.825, B: 0.2104},
	{A: 0.85, B: 0.2105},
	{A: 0.875, B: 0.2106},
	{A: 0.90, B: 0.2109},
	{A: 0.925, B: 0.2183},
	{A: 0.95, B: 0.2571},
	{A: 0.975, B: 0.3358},
	{A: 1.0, B: 0.4068},
	{A: 1.025, B: 0.4378},
	{A: 1.05, B: 0.4476},
	{A: 1.075, B: 0.4493},
	{A: 1.10, B: 0.4477},
	{A: 1.125, B: 0.4450},
	{A: 1.15, B: 0.4419},
	{A: 1.20, B: 0.4353},
	{A: 1.25, B: 0.4283},
	{A: 1.30, B: 0.4208},
	{A: 1.35, B: 0.4133},
	{A: 1.40, B: 0.4059},
	{A: 1.45, B: 0.3986},
	{A: 1.50, B: 0.3915},
	{A: 1.55, B: 0.3845},
	{A: 1.60, B: 0.3777},
	{A: 1.65, B: 0.3710},
	{A: 1.70, B: 0.3645},
	{A: 1.75, B: 0.3581},
	{A: 1.80, B: 0.3519},
	{A: 1.85, B: 0.3458},
	{A: 1.90, B: 0.3400},
	{A: 1.95, B: 0.3343},
	{A: 2.00, B: 0.3288},
	{A: 2.05, B: 0.3234},
	{A: 2.10, B: 0.3182},
	{A: 2.15, B: 0.3131},
	{A: 2.20, B: 0.3081},
	{A: 2.25, B: 0.3032},
	{A: 2.30, B: 0.2983},
	{A: 2.35, B: 0.2937},
	{A: 2.40, B: 0.2891},
	{A: 2.45, B: 0.2845},
	{A: 2.50, B: 0.2802},
	{A: 2.60, B: 0.2720},
	{A: 2.70, B: 0.2642},
	{A: 2.80, B: 0.2569},
	{A: 2.90, B: 0.2499},
	{A: 3.00, B: 0.2432},
	{A: 3.10, B: 0.2368},
	{A: 3.20, B: 0.2308},
	{A: 3.30, B: 0.2251},
	{A: 3.40, B: 0.2197},
	{A: 3.50, B: 0.2147},
	{A: 3.60, B: 0.2101},
	{A: 3.70, B: 0.2058},
	{A: 3.80, B: 0.2019},
	{A: 3.90, B: 0.1983},
	{A: 4.00, B: 0.1950},
	{A: 4.20, B: 0.1890},
	{A: 4.40, B: 0.1837},
	{A: 4.60, B: 0.1791},
	{A: 4.80, B: 0.1750},
	{A: 5.00, B: 0.1713},
}

var g8Curve = CalculateCurve(g8Table)

var gSTable = []DataPoint{
	{A: 0.00, B: 0.4662},
	{A: 0.05, B: 0.4689},
	{A: 0.10, B: 0.4717},
	{A: 0.15, B: 0.4745},
	{A: 0.20, B: 0.4772},
	{A: 0.25, B: 0.4800},
	{A: 0.30, B: 0.4827},
	{A: 0.35, B: 0.4852},
	{A: 0.40, B: 0.4882},
	{A: 0.45, B: 0.4920},
	{A: 0.50, B: 0.4970},
	{A: 0.55, B: 0.5080},
	{A: 0.60, B: 0.5260},
	{A: 0.65, B: 0.5590},
	{A: 0.70, B: 0.5920},
	{A: 0.75, B: 0.6258},
	{A: 0.80, B: 0.6610},
	{A: 0.85, B: 0.6985},
	{A: 0.90, B: 0.7370},
	{A: 0.95, B: 0.7757},
	{A: 1.0, B: 0.8140},
	{A: 1.05, B: 0.8512},
	{A: 1.10, B: 0.8870},
	{A: 1.15, B: 0.9210},
	{A: 1.20, B: 0.9510},
	{A: 1.25, B: 0.9740},
	{A: 1.30, B: 0.9910},
	{A: 1.35, B: 0.9990},
	{A: 1.40, B: 1.0030},
	{A: 1.45, B: 1.0060},
	{A: 1.50, B: 1.0080},
	{A: 1.55, B: 1.0090},
	{A: 1.60, B: 1.0090},
	{A: 1.65, B: 1.0090},
	{A: 1.70, B: 1.0090},
	{A: 1.75, B: 1.0080},
	{A: 1.80, B: 1.0070},
	{A: 1.85, B: 1.0060},
	{A: 1.90, B: 1.0040},
	{A: 1.95, B: 1.0025},
	{A: 2.00, B: 1.0010},
	{A: 2.05, B: 0.9990},
	{A: 2.10, B: 0.9970},
	{A: 2.15, B: 0.9956},
	{A: 2.20, B: 0.9940},
	{A: 2.25, B: 0.9916},
	{A: 2.30, B: 0.9890},
	{A: 2.35, B: 0.9869},
	{A: 2.40, B: 0.9850},
	{A: 2.45, B: 0.9830},
	{A: 2.50, B: 0.9810},
	{A: 2.55, B: 0.9790},
	{A: 2.60, B: 0.9770},
	{A: 2.65, B: 0.9750},
	{A: 2.70, B: 0.9730},
	{A: 2.75, B: 0.9710},
	{A: 2.80, B: 0.9690},
	{A: 2.85, B: 0.9670},
	{A: 2.90, B: 0.9650},
	{A: 2.95, B: 0.9630},
	{A: 3.00, B: 0.9610},
	{A: 3.05, B: 0.9589},
	{A: 3.10, B: 0.9570},
	{A: 3.15, B: 0.9555},
	{A: 3.20, B: 0.9540},
	{A: 3.25, B: 0.9520},
	{A: 3.30, B: 0.9500},
	{A: 3.35, B: 0.9485},
	{A: 3.40, B: 0.9470},
	{A: 3.45, B: 0.9450},
	{A: 3.50, B: 0.9430},
	{A: 3.55, B: 0.9414},
	{A: 3.60, B: 0.9400},
	{A: 3.65, B: 0.9385},
	{A: 3.70, B: 0.9370},
	{A: 3.75, B: 0.9355},
	{A: 3.80, B: 0.9340},
	{A: 3.85, B: 0.9325},
	{A: 3.90, B: 0.9310},
	{A: 3.95, B: 0.9295},
	{A: 4.00, B: 0.9280},
}

var gSCurve = CalculateCurve(gSTable)

//CalculateCurve calculates a curve for CalculateByCurve function using pretabulated or radar data
func CalculateCurve(dataPoints []DataPoint) []CurvePoint {
	var curve []CurvePoint
	var numPoints = len(dataPoints)
	var i int
	var x1, x2, x3, y1, y2, y3, a, b, c float64

	curve = make([]CurvePoint, numPoints)
	var rate = (dataPoints[1].B - dataPoints[0].B) / (dataPoints[1].A - dataPoints[0].A)
	curve[0] = CurvePoint{A: 0, B: rate, C: dataPoints[0].B - dataPoints[0].A*rate}

	// rest as 2nd degree polynomials on three adjacent points
	for i = 1; i < numPoints-1; i++ {
		x1 = dataPoints[i-1].A
		x2 = dataPoints[i].A
		x3 = dataPoints[i+1].A
		y1 = dataPoints[i-1].B
		y2 = dataPoints[i].B
		y3 = dataPoints[i+1].B
		a = ((y3-y1)*(x2-x1) - (y2-y1)*(x3-x1)) / ((x3*x3-x1*x1)*(x2-x1) - (x2*x2-x1*x1)*(x3-x1))
		b = (y2 - y1 - a*(x2*x2-x1*x1)) / (x2 - x1)
		c = y1 - (a*x1*x1 + b*x1)
		curve[i] = CurvePoint{A: a, B: b, C: c}
	}
	curve[numPoints-1] = CurvePoint{0, 0, dataPoints[numPoints-1].B}
	return curve
}

//CalculateByCurve calculates a drag value using pretabulted or data data and curve created by CalculateCurve
func CalculateByCurve(data []DataPoint, curve []CurvePoint, mach float64) float64 {
	var numPoints, m, mlo, mhi, mid int

	numPoints = len(curve)
	mlo = 0
	mhi = numPoints - 1

	for (mhi - mlo) > 1 {
		mid = int(math.Floor(float64(mhi+mlo) / 2.0))
		if data[mid].A < mach {
			mlo = mid
		} else {
			mhi = mid
		}
	}

	if (data[mhi].A - mach) > (mach - data[mlo].A) {
		m = mlo
	} else {
		m = mhi
	}

	return curve[m].C + mach*(curve[m].B+curve[m].A*mach)
}