29 lines
717 B
Go
29 lines
717 B
Go
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package internal
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import "math"
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const (
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earthEquatorialRadius = 6378137.0
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earthPolarRadius = 6356752.3
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)
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// HeightDegreeByLat 高度对应地平线下角 / horizon dip at latitude.
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func HeightDegreeByLat(height, lat float64) float64 {
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radius := geocentricRadius(lat)
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return math.Acos(radius/(radius+height)) * 180 / math.Pi
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}
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func geocentricRadius(lat float64) float64 {
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cosLat := math.Cos(lat * math.Pi / 180)
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sinLat := math.Sin(lat * math.Pi / 180)
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a := earthEquatorialRadius * earthEquatorialRadius * cosLat
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a *= a
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b := earthPolarRadius * earthPolarRadius * sinLat
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b *= b
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c := earthEquatorialRadius * cosLat
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c *= c
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d := earthPolarRadius * sinLat
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d *= d
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return math.Sqrt((a + b) / (c + d))
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}
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