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Go: added function horizonDipAngle.

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This commit is contained in:
Don Cross
2023-10-27 13:15:59 -04:00
parent 0b8336006f
commit 9c7dd495b1
2 changed files with 52 additions and 0 deletions
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26
generate/template/astronomy.go
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@@ -1605,6 +1605,32 @@ func findAscent(depth int, context SearchContext, maxDerivAlt float64, t1, t2 As
return ascent
}
func horizonDipAngle(observer Observer, metersAboveGround float64) float64 {
// Calculate the effective radius of the Earth at ground level below the observer.
// Correct for the Earth's oblateness.
phi := RadiansFromDegrees(observer.Latitude)
sinphi := math.Sin(phi)
cosphi := math.Cos(phi)
c := 1.0 / math.Hypot(cosphi, sinphi*EarthFlattening)
s := c * (EarthFlattening * EarthFlattening)
htkm := (observer.Height - metersAboveGround) / 1000.0 // height of ground above sea level
ach := EarthEquatorialRadiusKm*c + htkm
ash := EarthEquatorialRadiusKm*s + htkm
radiusMeters := 1000.0 * math.Hypot(ach*cosphi, ash*sinphi)
// Correct refraction of a ray of light traveling tangent to the Earth's surface.
// Based on: https://www.largeformatphotography.info/sunmooncalc/SMCalc.js
// which in turn derives from:
// Sweer, John. 1938. The Path of a Ray of Light Tangent to the Surface of the Earth.
// Journal of the Optical Society of America 28 (September):327-329.
// k = refraction index
k := 0.175 * math.Pow(1.0-(6.5e-3/283.15)*(observer.Height-(2.0/3.0)*metersAboveGround), 3.256)
// Calculate how far below the observer's horizontal plane the observed horizon dips.
return DegreesFromRadians(-(math.Sqrt(2*(1-k)*metersAboveGround/radiusMeters) / (1 - k)))
}
//--- Generated code begins here ------------------------------------------------------------------
//$ASTRO_CONSTEL()

26
source/golang/astronomy.go
View File

@@ -1605,6 +1605,32 @@ func findAscent(depth int, context SearchContext, maxDerivAlt float64, t1, t2 As
return ascent
}
func horizonDipAngle(observer Observer, metersAboveGround float64) float64 {
// Calculate the effective radius of the Earth at ground level below the observer.
// Correct for the Earth's oblateness.
phi := RadiansFromDegrees(observer.Latitude)
sinphi := math.Sin(phi)
cosphi := math.Cos(phi)
c := 1.0 / math.Hypot(cosphi, sinphi*EarthFlattening)
s := c * (EarthFlattening * EarthFlattening)
htkm := (observer.Height - metersAboveGround) / 1000.0 // height of ground above sea level
ach := EarthEquatorialRadiusKm*c + htkm
ash := EarthEquatorialRadiusKm*s + htkm
radiusMeters := 1000.0 * math.Hypot(ach*cosphi, ash*sinphi)
// Correct refraction of a ray of light traveling tangent to the Earth's surface.
// Based on: https://www.largeformatphotography.info/sunmooncalc/SMCalc.js
// which in turn derives from:
// Sweer, John. 1938. The Path of a Ray of Light Tangent to the Surface of the Earth.
// Journal of the Optical Society of America 28 (September):327-329.
// k = refraction index
k := 0.175 * math.Pow(1.0-(6.5e-3/283.15)*(observer.Height-(2.0/3.0)*metersAboveGround), 3.256)
// Calculate how far below the observer's horizontal plane the observed horizon dips.
return DegreesFromRadians(-(math.Sqrt(2*(1-k)*metersAboveGround/radiusMeters) / (1 - k)))
}
//--- Generated code begins here ------------------------------------------------------------------
var constelNames = [...]constelInfo{