117 lines
4.6 KiB
Go
117 lines
4.6 KiB
Go
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package sundial
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import (
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"math"
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"time"
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"b612.me/astro/sun"
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)
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// TrueSolarTime 真太阳时 / apparent solar time.
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//
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// 返回 date 在经度 lon 处对应的真太阳时，口径沿用 `sun.ApparentSolarTime`。
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// Returns the apparent solar time for date at longitude lon.
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func TrueSolarTime(date time.Time, lon float64) time.Time {
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return sun.ApparentSolarTime(date, lon)
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}
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// MeanSolarTime 地方平太阳时 / local mean solar time.
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//
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// 返回 date 在经度 lon 处对应的地方平太阳时，结果时区为按经度换算的地方平太阳时区。
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// 该实现直接按“真太阳时 - 均时差”构造，以与本仓库的真太阳时和均时差口径保持一致。
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// Returns the local mean solar time for date at longitude lon. The result uses
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// a synthetic local-mean-solar time zone derived from longitude and is built as
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// apparent solar time minus equation of time to keep the package's conventions aligned.
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func MeanSolarTime(date time.Time, lon float64) time.Time {
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return TrueSolarTime(date, lon).Add(time.Duration(-sun.EquationTime(date) * float64(time.Hour)))
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}
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// HourAngle 太阳时角 / solar hour angle.
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//
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// 返回经度 lon 处的有符号太阳时角，单位度。上午为负，下午为正，中午为 0°。
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// Returns the signed apparent-solar hour angle at longitude lon, in degrees.
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func HourAngle(date time.Time, lon float64) float64 {
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return normalizeSigned180(sun.HourAngle(date, lon, 0))
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}
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// MeanSolarHourAngle 平太阳时对应的太阳时角 / hour angle for local mean solar time.
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//
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// date 负责提供地方平太阳时日期与时区，原有钟面时间会被 meanSolarHours 替换；
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// meanSolarHours 为地方平太阳时钟面读数，单位小时，例如 9.5 表示地方平太阳时 09:30。
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// 返回对应的视太阳时角，单位度，上午为负，下午为正。
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func MeanSolarHourAngle(date time.Time, meanSolarHours float64) float64 {
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if !isFinite(meanSolarHours) {
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return math.NaN()
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}
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sampleTime := dateWithClockHours(date, meanSolarHours)
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return normalizeSigned180(HourAngle(sampleTime, longitudeFromTimeZone(sampleTime)))
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}
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// ZoneTimeHourAngle 区时对应的太阳时角 / hour angle for zone time.
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//
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// zoneTimeHours 为 date 所在时区下的钟面读数，单位小时；lon 为当地经度，东正西负。
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// 返回该区时在给定经度上对应的视太阳时角，单位度，上午为负，下午为正。
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// date 提供民用日期和时区；其原有钟面时间会被 zoneTimeHours 替换。
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func ZoneTimeHourAngle(date time.Time, lon, zoneTimeHours float64) float64 {
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if !isFinite(zoneTimeHours) || !isFinite(lon) {
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return math.NaN()
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}
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return normalizeSigned180(HourAngle(dateWithClockHours(date, zoneTimeHours), lon))
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}
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// HorizontalHourLineAngle 水平日晷时线角 / horizontal sundial hour-line angle.
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//
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// lat 为纬度（北正南负），hourAngle 为有符号太阳时角，单位度。返回值是相对午线的时线角，
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// 上午在东侧为负，下午在西侧为正。
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// lat is the observer latitude in degrees and hourAngle is the signed solar
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// hour angle in degrees. The result is the hour-line angle from the noon line:
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// east/morning is negative and west/afternoon is positive.
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func HorizontalHourLineAngle(lat, hourAngle float64) float64 {
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if !isFinite(hourAngle) || !isFinite(lat) {
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return math.NaN()
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}
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hourAngle = normalizeSigned180(hourAngle)
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latRad := lat * math.Pi / 180
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hourAngleRad := hourAngle * math.Pi / 180
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return math.Atan2(math.Sin(latRad)*math.Sin(hourAngleRad), math.Cos(hourAngleRad)) * 180 / math.Pi
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}
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// HorizontalHourLineAngleAt 水平日晷时线角 / horizontal sundial hour-line angle.
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//
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// 先按给定时刻和经度求瞬时视太阳时角，再结合纬度返回水平日晷的时线角。
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func HorizontalHourLineAngleAt(date time.Time, lon, lat float64) float64 {
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return HorizontalHourLineAngle(lat, HourAngle(date, lon))
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}
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func dateWithClockHours(date time.Time, hours float64) time.Time {
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startOfDay := time.Date(date.Year(), date.Month(), date.Day(), 0, 0, 0, 0, date.Location())
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return startOfDay.Add(time.Duration(hours * float64(time.Hour)))
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}
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func longitudeFromTimeZone(date time.Time) float64 {
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_, offsetSeconds := date.Zone()
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return float64(offsetSeconds) / 240.0
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}
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func clockHours(date time.Time) float64 {
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return float64(date.Hour()) +
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float64(date.Minute())/60 +
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float64(date.Second())/3600 +
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float64(date.Nanosecond())/3.6e12
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}
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func normalizeSigned180(value float64) float64 {
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value = math.Mod(value, 360)
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if value < -180 {
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value += 360
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}
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if value >= 180 {
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value -= 360
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}
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return value
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}
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func isFinite(value float64) bool {
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return !math.IsNaN(value) && !math.IsInf(value, 0)
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}
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