Chief Ray

Photogrammetric and Mapping Software


 

Support for stellar catalogs

  • Accepts data and units that are standard for FK5 and Hipparcos star catalogs

    • Right ascension, declination

    • Proper motion in right ascension and declination

    • Parallax

  • Conversion between Hipparcos epoch (J1991.25) and FK5 epoch (J2000.0)

Conversion from star catalog mean place to apparent place, topocentric place, and local horizon coordinates

  • Apparent place: Position of star at some date and time

    • In the coordinates system defined by the true equator and equinox of date

    • Ignoring atmospheric refraction

    • As seen from the Earth's center of mass

  • Topocentric place:  Position of star at some date and time

    • In the coordinate system defined by the true equator and equinox of date

    • Ignoring atmospheric refraction

    • As seen from a specific location on Earth

  • Local horizon coordinates: Position of star at some date and time

    • In local azimuth and elevation coordinates

    • Including atmospheric refraction (optional)

    • As seen from a specific location on Earth

Time conversions among UT1, UTC, TAI, TDT, TDB

  • UT1 Time corresponding to Earth rotation

  • UTC Universal coordinated time (Civil time)

  • TAI Atomic time

  • TDT Terrestrial dynamic time (TAI + 32.184 sec)

  • TDB Barycentric dynamic time (removes general relativistic tidal effects from TDT)

  • General conversion chain:      TDB ↔ TDT ↔ TAI ↔ UTC ↔ UT1

ECF ↔ ECI conversion using quaternions

 

  • XECI = q XECF q*

    • q = qP* qN* qS qW  expresses that attitude of the ECF system relative to the ECI system

    • qP  (precession) accounts for precession of the mean celestial system

    • qN  (nutation) accounts for the nutation correction from the mean celestial system of date

    • qS  (spin) accounts for earth rotation

    • qW  (wobble) accounts for polar motion

Earth Orientation Parameters

  • Precision offsets and corrections that must be measured, not computed

    • Polar Motion (x,y)

    • UTI UTC

    • Nutation offsets (Dpsi, Deps)

  • Interpolated from files containing the IERS CO4 solution (daily values from 1962 to present)

 

For more information, contact Chief Ray .

 

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