90 lines
3.3 KiB
Go
90 lines
3.3 KiB
Go
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package basic
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import "math"
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const (
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refractionStandardPressureHPa = 1010.0
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refractionStandardTemperatureK = 283.0
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refractionAbsoluteZeroC = -273.15
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refractionLowerLimitAltitudeDeg = -5.0
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refractionUpperLimitAltitudeDeg = 90.0
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)
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// RefractionFromApparentAltitude 大气折射修正量，单位度；输入为视高度角。
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// 返回值应从真高度角加上后得到视高度角。
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func RefractionFromApparentAltitude(apparentAltitude, pressureHPa, temperatureC float64) float64 {
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if !validRefractionInputs(apparentAltitude, pressureHPa, temperatureC) {
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return math.NaN()
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}
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if apparentAltitude < refractionLowerLimitAltitudeDeg || apparentAltitude > refractionUpperLimitAltitudeDeg {
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return 0
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}
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angle := (apparentAltitude + 10.3/(apparentAltitude+5.11)) * math.Pi / 180
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return refractionScale(pressureHPa, temperatureC) * (1.02 / math.Tan(angle)) / 60
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}
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// TrueAltitude 真高度角，单位度；输入为视高度角。
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func TrueAltitude(apparentAltitude, pressureHPa, temperatureC float64) float64 {
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refraction := RefractionFromApparentAltitude(apparentAltitude, pressureHPa, temperatureC)
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if math.IsNaN(refraction) {
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return math.NaN()
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}
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return apparentAltitude - refraction
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}
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// ApparentAltitude 视高度角，单位度；输入为真高度角。
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func ApparentAltitude(trueAltitude, pressureHPa, temperatureC float64) float64 {
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if !validRefractionInputs(trueAltitude, pressureHPa, temperatureC) {
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return math.NaN()
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}
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if trueAltitude < refractionLowerLimitAltitudeDeg || trueAltitude > refractionUpperLimitAltitudeDeg {
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return trueAltitude
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}
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estimate := trueAltitude + RefractionFromApparentAltitude(trueAltitude, pressureHPa, temperatureC)
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for i := 0; i < 8; i++ {
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refraction := RefractionFromApparentAltitude(estimate, pressureHPa, temperatureC)
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if math.IsNaN(refraction) {
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return math.NaN()
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}
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value := estimate - refraction - trueAltitude
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if math.Abs(value) < 1e-12 {
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break
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}
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const delta = 1e-6
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refractionPlus := RefractionFromApparentAltitude(estimate+delta, pressureHPa, temperatureC)
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refractionMinus := RefractionFromApparentAltitude(estimate-delta, pressureHPa, temperatureC)
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if math.IsNaN(refractionPlus) || math.IsNaN(refractionMinus) {
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return math.NaN()
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}
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derivative := 1 - (refractionPlus-refractionMinus)/(2*delta)
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if derivative == 0 {
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break
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}
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estimate -= value / derivative
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}
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return estimate
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}
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// RefractionFromTrueAltitude 大气折射修正量，单位度；输入为真高度角。
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// 返回值应从真高度角加上后得到视高度角。
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func RefractionFromTrueAltitude(trueAltitude, pressureHPa, temperatureC float64) float64 {
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apparentAltitude := ApparentAltitude(trueAltitude, pressureHPa, temperatureC)
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if math.IsNaN(apparentAltitude) {
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return math.NaN()
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}
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return apparentAltitude - trueAltitude
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}
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func validRefractionInputs(altitude, pressureHPa, temperatureC float64) bool {
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return !(math.IsNaN(altitude) || math.IsInf(altitude, 0) ||
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math.IsNaN(pressureHPa) || math.IsInf(pressureHPa, 0) || pressureHPa <= 0 ||
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math.IsNaN(temperatureC) || math.IsInf(temperatureC, 0) || temperatureC <= refractionAbsoluteZeroC)
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}
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func refractionScale(pressureHPa, temperatureC float64) float64 {
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return pressureHPa / refractionStandardPressureHPa * refractionStandardTemperatureK / (273 + temperatureC)
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}
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