41 lines
1.1 KiB
Go
41 lines
1.1 KiB
Go
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package tools
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import "math"
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// DistanceUnit 距离输入单位 / a unit accepted for distance input.
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type DistanceUnit uint8
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const (
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// DistanceParsec 秒差距 / parsec.
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DistanceParsec DistanceUnit = iota
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// DistanceLightYear 光年 / light-year.
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DistanceLightYear
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// DistanceAU 天文单位 / astronomical unit.
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DistanceAU
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)
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// 天文单位与光年取 IAU 定义值，秒差距由精确关系 648000/π 天文单位导出。
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const (
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AstronomicalUnitKilometers = 149597870.7
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LightYearKilometers = 9460730472580.8
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parsecAU = 648000 / math.Pi
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)
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// DistanceToParsecs 把给定单位的距离换算为秒差距 / converts a distance in the given unit to parsecs.
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//
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// 非正数、NaN 与未知单位返回 NaN。
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func DistanceToParsecs(value float64, unit DistanceUnit) float64 {
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if math.IsNaN(value) || math.IsInf(value, 0) || value <= 0 {
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return math.NaN()
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}
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switch unit {
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case DistanceParsec:
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return value
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case DistanceLightYear:
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return value * LightYearKilometers / AstronomicalUnitKilometers / parsecAU
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case DistanceAU:
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return value / parsecAU
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}
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return math.NaN()
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}
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