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### B.1.6 CoordsRadians

Functions for angle transformations and manipulations, based on radians rather than degrees. In particular, methods for translating between radians and HH:MM:SS.S or DDD:MM:SS.S type sexagesimal representations are provided.

`radiansToDms( rad )`
  Converts an angle in radians to a formatted degrees:minutes:seconds string. No fractional part of the seconds field is given.

  - Parameters:
    - `rad` (floating point): angle in radians
  - Return value
    - (String): DMS-format string representing `rad`
`radiansToDms( rad, secFig )`
  Converts an angle in radians to a formatted degrees:minutes:seconds string with a given number of decimal places in the seconds field.

  - Parameters:
    - `rad` (floating point): angle in radians
    - `secFig` (integer): number of decimal places in the seconds field
  - Return value
    - (String): DMS-format string representing `rad`
`radiansToHms( rad )`
  Converts an angle in radians to a formatted hours:minutes:seconds string. No fractional part of the seconds field is given.

  - Parameters:
    - `rad` (floating point): angle in radians
  - Return value
    - (String): HMS-format string representing `rad`
`radiansToHms( rad, secFig )`
  Converts an angle in radians to a formatted hours:minutes:seconds string with a given number of decimal places in the seconds field.

  - Parameters:
    - `rad` (floating point): angle in radians
    - `secFig` (integer): number of decimal places in the seconds field
  - Return value
    - (String): HMS-format string representing `rad`
`dmsToRadians( dms )`
  Converts a formatted degrees:minutes:seconds string to an angle in radians. Delimiters may be colon, space, characters `dm[s]`, or some others. Additional spaces and leading +/- are permitted. The :seconds part is optional.

  - Parameters:
    - `dms` (String): formatted DMS string
  - Return value
    - (floating point): angle in radians specified by `dms`
`hmsToRadians( hms )`
  Converts a formatted hours:minutes:seconds string to an angle in radians. Delimiters may be colon, space, characters `hm[s]`, or some others. Additional spaces and leading +/- are permitted. The :seconds part is optional.

  - Parameters:
    - `hms` (String): formatted HMS string
  - Return value
    - (floating point): angle in radians specified by `hms`
`dmsToRadians( deg, min, sec )`
  Converts degrees, minutes, seconds to an angle in radians.

  In conversions of this type, one has to be careful to get the sign right in converting angles which are between 0 and -1 degrees. This routine uses the sign bit of the `deg` argument, taking care to distinguish between +0 and -0 (their internal representations are different for floating point values). It is illegal for the `min` or `sec` arguments to be negative.

  - Parameters:
    - `deg` (floating point): degrees part of angle
    - `min` (floating point): minutes part of angle
    - `sec` (floating point): seconds part of angle
  - Return value
    - (floating point): specified angle in radians
`hmsToRadians( hour, min, sec )`
  Converts hours, minutes, seconds to an angle in radians.

  In conversions of this type, one has to be careful to get the sign right in converting angles which are between 0 and -1 hours. This routine uses the sign bit of the `hour` argument, taking care to distinguish between +0 and -0 (their internal representations are different for floating point values).

  - Parameters:
    - `hour` (floating point): degrees part of angle
    - `min` (floating point): minutes part of angle
    - `sec` (floating point): seconds part of angle
  - Return value
    - (floating point): specified angle in radians
`skyDistanceRadians( ra1, dec1, ra2, dec2 )`
  Calculates the separation (distance around a great circle) of two points on the sky in radians.

  - Parameters:
    - `ra1` (floating point): right ascension of point 1 in radians
    - `dec1` (floating point): declination of point 1 in radians
    - `ra2` (floating point): right ascension of point 2 in radians
    - `dec2` (floating point): declination of point 2 in radians
  - Return value
    - (floating point): angular distance between point 1 and point 2 in radians
`posAngRadians( ra1, dec1, ra2, dec2 )`
  Calculates the position angle between two points on the sky in radians. The result is in the range +/-pi. If point 2 is due east of point 1, the result is +pi/2. Zero is returned if the points are coincident.

  - Parameters:
    - `ra1` (floating point): right ascension of point 1 in radians
    - `dec1` (floating point): declination of point 1 in radians
    - `ra2` (floating point): right ascension of point 2 in radians
    - `dec2` (floating point): declination of point 2 in radians
  - Return value
    - (floating point): bearing in radians of point 2 from point 1
`polarDistanceRadians( ra1, dec1, radius1, ra2, dec2, radius2 )`
  Calculates the distance in three dimensional space between two points specified in spherical polar coordinates.

  - Parameters:
    - `ra1` (floating point): right ascension of point 1 in radians
    - `dec1` (floating point): declination of point1 in radians
    - `radius1` (floating point): distance from origin of point1
    - `ra2` (floating point): right ascension of point 2 in radians
    - `dec2` (floating point): declination of point2 in radians
    - `radius2` (floating point): distance from origin of point2
  - Return value
    - (floating point): the linear distance between point1 and point2; units are as for `radius1` and `radius2`
`hoursToRadians( hours )`
  Converts hours to radians.

  - Parameters:
    - `hours` (floating point): angle in hours
  - Return value
    - (floating point): angle in radians
`degreesToRadians( deg )`
  Converts degrees to radians.

  - Parameters:
    - `deg` (floating point): angle in degrees
  - Return value
    - (floating point): angle in radians
`radiansToDegrees( rad )`
  Converts radians to degrees.

  - Parameters:
    - `rad` (floating point): angle in radians
  - Return value
    - (floating point): angle in degrees
`raFK4toFK5radians( raFK4, decFK4 )`
  Converts a B1950.0 FK4 position to J2000.0 FK5 at an epoch of B1950.0 yielding Right Ascension. This assumes zero proper motion in the FK5 frame.

  - Parameters:
    - `raFK4` (floating point): right ascension in B1950.0 FK4 system (radians)
    - `decFK4` (floating point): declination in B1950.0 FK4 system (radians)
  - Return value
    - (floating point): right ascension in J2000.0 FK5 system (radians)
`decFK4toFK5radians( raFK4, decFK4 )`
  Converts a B1950.0 FK4 position to J2000.0 FK5 at an epoch of B1950.0 yielding Declination This assumes zero proper motion in the FK5 frame.

  - Parameters:
    - `raFK4` (floating point): right ascension in B1950.0 FK4 system (radians)
    - `decFK4` (floating point): declination in B1950.0 FK4 system (radians)
  - Return value
    - (floating point): declination in J2000.0 FK5 system (radians)
`raFK5toFK4radians( raFK5, decFK5 )`
  Converts a J2000.0 FK5 position to B1950.0 FK4 at an epoch of B1950.0 yielding Declination. This assumes zero proper motion, parallax and radial velocity in the FK5 frame.

  - Parameters:
    - `raFK5` (floating point): right ascension in J2000.0 FK5 system (radians)
    - `decFK5` (floating point): declination in J2000.0 FK5 system (radians)
  - Return value
    - (floating point): right ascension in the FK4 system (radians)
`decFK5toFK4radians( raFK5, decFK5 )`
  Converts a J2000.0 FK5 position to B1950.0 FK4 at an epoch of B1950.0 yielding Declination. This assumes zero proper motion, parallax and radial velocity in the FK5 frame.

  - Parameters:
    - `raFK5` (floating point): right ascension in J2000.0 FK5 system (radians)
    - `decFK5` (floating point): declination in J2000.0 FK5 system (radians)
  - Return value
    - (floating point): right ascension in the FK4 system (radians)
`raFK4toFK5Radians( raFK4, decFK4, bepoch )`
  Converts a B1950.0 FK4 position to J2000.0 FK5 yielding Right Ascension. This assumes zero proper motion in the FK5 frame. The `bepoch` parameter is the epoch at which the position in the FK4 frame was determined.

  - Parameters:
    - `raFK4` (floating point): right ascension in B1950.0 FK4 system (radians)
    - `decFK4` (floating point): declination in B1950.0 FK4 system (radians)
    - `bepoch` (floating point): Besselian epoch
  - Return value
    - (floating point): right ascension in J2000.0 FK5 system (radians)
`decFK4toFK5Radians( raFK4, decFK4, bepoch )`
  Converts a B1950.0 FK4 position to J2000.0 FK5 yielding Declination. This assumes zero proper motion in the FK5 frame. The `bepoch` parameter is the epoch at which the position in the FK4 frame was determined.

  - Parameters:
    - `raFK4` (floating point): right ascension in B1950.0 FK4 system (radians)
    - `decFK4` (floating point): declination in B1950.0 FK4 system (radians)
    - `bepoch` (floating point): Besselian epoch
  - Return value
    - (floating point): declination in J2000.0 FK5 system (radians)
`raFK5toFK4Radians( raFK5, decFK5, bepoch )`
  Converts a J2000.0 FK5 position to B1950.0 FK4 yielding Declination. This assumes zero proper motion, parallax and radial velocity in the FK5 frame.

  - Parameters:
    - `raFK5` (floating point): right ascension in J2000.0 FK5 system (radians)
    - `decFK5` (floating point): declination in J2000.0 FK5 system (radians)
    - `bepoch` (floating point): Besselian epoch
  - Return value
    - (floating point): right ascension in the FK4 system (radians)
`decFK5toFK4Radians( raFK5, decFK5, bepoch )`
  Converts a J2000.0 FK5 position to B1950.0 FK4 yielding Declination. This assumes zero proper motion, parallax and radial velocity in the FK5 frame.

  - Parameters:
    - `raFK5` (floating point): right ascension in J2000.0 FK5 system (radians)
    - `decFK5` (floating point): declination in J2000.0 FK5 system (radians)
    - `bepoch` (floating point): Besselian epoch
  - Return value
    - (floating point): right ascension in the FK4 system (radians)
`DEGREE_RADIANS`
  The size of one degree in radians.

`HOUR_RADIANS`
  The size of one hour of right ascension in radians.

`ARC_MINUTE_RADIANS`
  The size of one arcminute in radians.

`ARC_SECOND_RADIANS`
  The size of one arcsecond in radians.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
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