221 lines
8.0 KiB
Go
221 lines
8.0 KiB
Go
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package coord
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import "math"
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// Galactic 银道坐标 / galactic coordinates.
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type Galactic struct {
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Lon float64 // 银经，单位度 / galactic longitude in degrees.
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Lat float64 // 银纬，单位度 / galactic latitude in degrees.
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}
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// SOFA ICRS2G/G2ICRS fixed rotation matrix.
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// Source: IAU SOFA 2023-10-11, iauIcrs2g/iauG2icrs.
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var icrsToGalacticMatrix = [3][3]float64{
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{-0.054875560416215368492398900454, -0.873437090234885048760383168409, -0.483835015548713226831774175116},
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{+0.494109427875583673525222371358, -0.444829629960011178146614061616, +0.746982244497218890527388004556},
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{-0.867666149019004701181616534570, -0.198076373431201528180486091412, +0.455983776175066922272100478348},
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}
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// EclipticToEquatorialByObliquity 黄道转赤道坐标（指定黄赤交角） / ecliptic to equatorial by obliquity.
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//
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// lon: 黄经，单位度
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// lat: 黄纬，单位度
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// obliquity: 黄赤交角，单位度
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//
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// 返回：
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//
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// 赤经 RA，单位度；赤纬 Dec，单位度
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func EclipticToEquatorialByObliquity(lon, lat, obliquity float64) Equatorial {
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sinLon, cosLon := sinCosDeg(lon)
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sinLat, cosLat := sinCosDeg(lat)
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sinObliquity, cosObliquity := sinCosDeg(obliquity)
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ra := normalize360(math.Atan2(sinLon*cosObliquity-math.Tan(lat*math.Pi/180)*sinObliquity, cosLon) * 180 / math.Pi)
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dec := math.Asin(clampUnit(sinLat*cosObliquity+cosLat*sinObliquity*sinLon)) * 180 / math.Pi
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return Equatorial{RA: ra, Dec: dec}
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}
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// EquatorialToEclipticByObliquity 赤道转黄道坐标（指定黄赤交角） / equatorial to ecliptic by obliquity.
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//
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// ra: 赤经，单位度
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// dec: 赤纬，单位度
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// obliquity: 黄赤交角，单位度
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//
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// 返回：
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//
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// 黄经 Lon，单位度；黄纬 Lat，单位度
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func EquatorialToEclipticByObliquity(ra, dec, obliquity float64) Ecliptic {
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sinRA, cosRA := sinCosDeg(ra)
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sinDec, cosDec := sinCosDeg(dec)
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sinObliquity, cosObliquity := sinCosDeg(obliquity)
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lon := normalize360(math.Atan2(sinRA*cosObliquity+math.Tan(dec*math.Pi/180)*sinObliquity, cosRA) * 180 / math.Pi)
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lat := math.Asin(clampUnit(sinDec*cosObliquity-cosDec*sinObliquity*sinRA)) * 180 / math.Pi
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return Ecliptic{Lon: lon, Lat: lat}
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}
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// HourAngleDeclinationToHorizontal 时角赤纬转地平坐标 / horizontal coordinates from hour angle and declination.
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//
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// hourAngle: 时角，单位度
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// declination: 赤纬，单位度
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// latitude: 观测者地理纬度，单位度，北正南负
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//
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// 返回：
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//
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// 方位角 Azimuth（正北为0，顺时针增加）、高度角 Altitude、天顶距 Zenith，均为度
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func HourAngleDeclinationToHorizontal(hourAngle, declination, latitude float64) Horizontal {
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sinLatitude, cosLatitude := sinCosDeg(latitude)
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sinDeclination, cosDeclination := sinCosDeg(declination)
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sinHourAngle, cosHourAngle := sinCosDeg(hourAngle)
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altitude := math.Asin(clampUnit(sinLatitude*sinDeclination+cosLatitude*cosDeclination*cosHourAngle)) * 180 / math.Pi
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azimuth := normalize360(math.Atan2(-cosDeclination*sinHourAngle, cosLatitude*sinDeclination-sinLatitude*cosDeclination*cosHourAngle) * 180 / math.Pi)
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return Horizontal{
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Azimuth: azimuth,
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Altitude: altitude,
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Zenith: 90 - altitude,
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HourAngle: normalize360(hourAngle),
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}
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}
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// HorizontalToHourAngleDeclination 地平坐标转时角赤纬 / hour angle and declination from horizontal coordinates.
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//
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// azimuth: 方位角，单位度，正北为0，顺时针增加
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// altitude: 高度角，单位度
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// latitude: 观测者地理纬度，单位度，北正南负
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//
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// 返回：
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//
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// 时角 HourAngle，单位度；赤纬 Declination，单位度
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func HorizontalToHourAngleDeclination(azimuth, altitude, latitude float64) (hourAngle, declination float64) {
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sinLatitude, cosLatitude := sinCosDeg(latitude)
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sinAltitude, cosAltitude := sinCosDeg(altitude)
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sinAzimuth, cosAzimuth := sinCosDeg(azimuth)
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declination = math.Asin(clampUnit(sinLatitude*sinAltitude+cosLatitude*cosAltitude*cosAzimuth)) * 180 / math.Pi
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sinHourAngle := -cosAltitude * sinAzimuth
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cosHourAngle := sinAltitude*cosLatitude - cosAltitude*sinLatitude*cosAzimuth
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hourAngle = normalize360(math.Atan2(sinHourAngle, cosHourAngle) * 180 / math.Pi)
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return hourAngle, declination
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}
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// EquatorialToHorizontalByLocalSiderealTime 赤道转地平坐标（指定地方恒星时） / equatorial to horizontal by local sidereal time.
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//
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// localSiderealTimeHours: 站点本地恒星时，单位小时
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// ra: 赤经，单位度
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// dec: 赤纬，单位度
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// latitude: 观测者地理纬度，单位度，北正南负
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//
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// 返回：
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//
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// 方位角 Azimuth（正北为0，顺时针增加）、高度角 Altitude、天顶距 Zenith，均为度；
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// 附带返回对应的时角 HourAngle，单位度
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//
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// 例：
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//
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// hz := coord.EquatorialToHorizontalByLocalSiderealTime(10.5, 83.6331, 22.0145, 31.2)
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func EquatorialToHorizontalByLocalSiderealTime(localSiderealTimeHours, ra, dec, latitude float64) Horizontal {
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hourAngle := normalize360(localSiderealTimeHours*15 - ra)
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return HourAngleDeclinationToHorizontal(hourAngle, dec, latitude)
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}
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// HorizontalToEquatorialByLocalSiderealTime 地平转赤道坐标（指定地方恒星时） / horizontal to equatorial by local sidereal time.
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//
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// localSiderealTimeHours: 站点本地恒星时，单位小时
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// azimuth: 方位角，单位度，正北为0，顺时针增加
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// altitude: 高度角，单位度
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// latitude: 观测者地理纬度，单位度，北正南负
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//
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// 返回：
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//
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// 赤经 RA，单位度；赤纬 Dec，单位度
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//
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// 例：
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//
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// eq := coord.HorizontalToEquatorialByLocalSiderealTime(10.5, 128.2, 37.6, 31.2)
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func HorizontalToEquatorialByLocalSiderealTime(localSiderealTimeHours, azimuth, altitude, latitude float64) Equatorial {
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hourAngle, declination := HorizontalToHourAngleDeclination(azimuth, altitude, latitude)
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ra := normalize360(localSiderealTimeHours*15 - hourAngle)
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return Equatorial{RA: ra, Dec: declination}
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}
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// EquatorialToGalactic 赤道转银道坐标 / equatorial to galactic coordinates.
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//
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// ra: ICRS 赤经，单位度
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// dec: ICRS 赤纬，单位度
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//
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// 返回：
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//
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// 银经 Lon，单位度；银纬 Lat，单位度
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func EquatorialToGalactic(ra, dec float64) Galactic {
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vector := sphericalToVector(ra, dec)
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rotated := matrixVectorMul(icrsToGalacticMatrix, vector)
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lon, lat := vectorToSpherical(rotated)
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return Galactic{Lon: lon, Lat: lat}
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}
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// GalacticToEquatorial 银道转赤道坐标 / galactic to equatorial coordinates.
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//
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// lon: 银经，单位度
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// lat: 银纬，单位度
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//
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// 返回：
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//
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// ICRS 赤经 RA，单位度；ICRS 赤纬 Dec，单位度
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func GalacticToEquatorial(lon, lat float64) Equatorial {
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vector := sphericalToVector(lon, lat)
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rotated := matrixTransposeVectorMul(icrsToGalacticMatrix, vector)
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ra, dec := vectorToSpherical(rotated)
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return Equatorial{RA: ra, Dec: dec}
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}
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func sinCosDeg(angle float64) (sinValue, cosValue float64) {
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return math.Sincos(angle * math.Pi / 180)
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}
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func normalize360(angle float64) float64 {
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angle = math.Mod(angle, 360)
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if angle < 0 {
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angle += 360
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}
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return angle
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}
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func clampUnit(value float64) float64 {
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if value > 1 {
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return 1
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}
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if value < -1 {
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return -1
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}
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return value
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}
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func sphericalToVector(lon, lat float64) [3]float64 {
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sinLon, cosLon := sinCosDeg(lon)
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sinLat, cosLat := sinCosDeg(lat)
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return [3]float64{cosLat * cosLon, cosLat * sinLon, sinLat}
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}
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func vectorToSpherical(vector [3]float64) (lon, lat float64) {
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lon = normalize360(math.Atan2(vector[1], vector[0]) * 180 / math.Pi)
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lat = math.Asin(clampUnit(vector[2])) * 180 / math.Pi
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return lon, lat
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}
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func matrixVectorMul(matrix [3][3]float64, vector [3]float64) [3]float64 {
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return [3]float64{
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matrix[0][0]*vector[0] + matrix[0][1]*vector[1] + matrix[0][2]*vector[2],
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matrix[1][0]*vector[0] + matrix[1][1]*vector[1] + matrix[1][2]*vector[2],
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matrix[2][0]*vector[0] + matrix[2][1]*vector[1] + matrix[2][2]*vector[2],
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}
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}
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func matrixTransposeVectorMul(matrix [3][3]float64, vector [3]float64) [3]float64 {
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return [3]float64{
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matrix[0][0]*vector[0] + matrix[1][0]*vector[1] + matrix[2][0]*vector[2],
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matrix[0][1]*vector[0] + matrix[1][1]*vector[1] + matrix[2][1]*vector[2],
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matrix[0][2]*vector[0] + matrix[1][2]*vector[1] + matrix[2][2]*vector[2],
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}
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}
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