Function apco13

Source

pub fn apco13(
    utc1: f64,
    utc2: f64,
    dut1: f64,
    elong: f64,
    phi: f64,
    hm: f64,
    xp: f64,
    yp: f64,
    phpa: f64,
    tc: f64,
    rh: f64,
    wl: f64,
    astrom: &mut IauAstrom,
    eo: &mut f64,
) -> Result<i32, i32>

Expand description

Prepare for ICRS <−> observed, terrestrial

For a terrestrial observer, prepare star-independent astrometry parameters for transformations between ICRS and observed coordinates. The caller supplies UTC, site coordinates, ambient air conditions and observing wavelength, and SOFA models are used to obtain the Earth ephemeris, CIP/CIO and refraction constants.

The parameters produced by this function are required in the parallax, light deflection, aberration, and bias-precession-nutation parts of the ICRS/CIRS transformations.

This function is part of the International Astronomical Union’s SOFA (Standards of Fundamental Astronomy) software collection.

Status: support function.

Given:

   utc1   double     UTC as a 2-part...
   utc2   double     ...quasi Julian Date (Notes 1,2)
   dut1   double     UT1-UTC (seconds, Note 3)
   elong  double     longitude (radians, east +ve, Note 4)
   phi    double     latitude (geodetic, radians, Note 4)
   hm     double     height above ellipsoid (m, geodetic, Notes 4,6)
   xp,yp  double     polar motion coordinates (radians, Note 5)
   phpa   double     pressure at the observer (hPa = mB, Note 6)
   tc     double     ambient temperature at the observer (deg C)
   rh     double     relative humidity at the observer (range 0-1)
   wl     double     wavelength (micrometers, Note 7)

Returned:

   astrom iauASTROM* star-independent astrometry parameters:
    pmt    double       PM time interval (SSB, Julian years)
    eb     double[3]    SSB to observer (vector, au)
    eh     double[3]    Sun to observer (unit vector)
    em     double       distance from Sun to observer (au)
    v      double[3]    barycentric observer velocity (vector, c)
    bm1    double       sqrt(1-|v|^2): reciprocal of Lorenz factor
    bpn    double[3][3] bias-precession-nutation matrix
    along  double       longitude + s' (radians)
    xpl    double       polar motion xp wrt local meridian (radians)
    ypl    double       polar motion yp wrt local meridian (radians)
    sphi   double       sine of geodetic latitude
    cphi   double       cosine of geodetic latitude
    diurab double       magnitude of diurnal aberration vector
    eral   double       "local" Earth rotation angle (radians)
    refa   double       refraction constant A (radians)
    refb   double       refraction constant B (radians)
   eo     double*    equation of the origins (ERA-GST, radians)

Returned (function value):

          int        status: +1 = dubious year (Note 2)
                              0 = OK
                             -1 = unacceptable date

Notes:

utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any convenient way between the two arguments, for example where utc1 is the Julian Day Number and utc2 is the fraction of a day.

However, JD cannot unambiguously represent UTC during a leap second unless special measures are taken. The convention in the present function is that the JD day represents UTC days whether the length is 86399, 86400 or 86401 SI seconds.

Applications should use the function iauDtf2d to convert from calendar date and time of day into 2-part quasi Julian Date, as it implements the leap-second-ambiguity convention just described.
The warning status “dubious year” flags UTCs that predate the introduction of the time scale or that are too far in the future to be trusted. See iauDat for further details.
UT1-UTC is tabulated in IERS bulletins. It increases by exactly one second at the end of each positive UTC leap second, introduced in order to keep UT1-UTC within +/- 0.9s. n.b. This practice is under review, and in the future UT1-UTC may grow essentially without limit.
The geographical coordinates are with respect to the WGS84 reference ellipsoid. TAKE CARE WITH THE LONGITUDE SIGN: the longitude required by the present function is east-positive (i.e. right-handed), in accordance with geographical convention.
The polar motion xp,yp can be obtained from IERS bulletins. The values are the coordinates (in radians) of the Celestial Intermediate Pole with respect to the International Terrestrial Reference System (see IERS Conventions 2003), measured along the meridians 0 and 90 deg west respectively. For many applications, xp and yp can be set to zero.

Internally, the polar motion is stored in a form rotated onto the local meridian.
If hm, the height above the ellipsoid of the observing station in meters, is not known but phpa, the pressure in hPa (=mB), is available, an adequate estimate of hm can be obtained from the expression
```
  hm = -29.3 * tsl * log ( phpa / 1013.25 );
```
where tsl is the approximate sea-level air temperature in K (See Astrophysical Quantities, C.W.Allen, 3rd edition, section 52). Similarly, if the pressure phpa is not known, it can be estimated from the height of the observing station, hm, as follows:
```
  phpa = 1013.25 * exp ( -hm / ( 29.3 * tsl ) );
```
Note, however, that the refraction is nearly proportional to the pressure and that an accurate phpa value is important for precise work.
The argument wl specifies the observing wavelength in micrometers. The transition from optical to radio is assumed to occur at 100 micrometers (about 3000 GHz).
It is advisable to take great care with units, as even unlikely values of the input parameters are accepted and processed in accordance with the models used.
In cases where the caller wishes to supply his own Earth ephemeris, Earth rotation information and refraction constants, the function iauApco can be used instead of the present function.
This is one of several functions that inserts into the astrom structure star-independent parameters needed for the chain of astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed.

The various functions support different classes of observer and portions of the transformation chain:

        functions         observer        transformation

     iauApcg iauApcg13    geocentric      ICRS <-> GCRS
     iauApci iauApci13    terrestrial     ICRS <-> CIRS
     iauApco iauApco13    terrestrial     ICRS <-> observed
     iauApcs iauApcs13    space           ICRS <-> GCRS
     iauAper iauAper13    terrestrial     update Earth rotation
     iauApio iauApio13    terrestrial     CIRS <-> observed

Those with names ending in "13" use contemporary SOFA models to
compute the various ephemerides.  The others accept ephemerides
supplied by the caller.

The transformation from ICRS to GCRS covers space motion,
parallax, light deflection, and aberration.  From GCRS to CIRS
comprises frame bias and precession-nutation.  From CIRS to
observed takes account of Earth rotation, polar motion, diurnal
aberration and parallax (unless subsumed into the ICRS <-> GCRS
transformation), and atmospheric refraction.

The context structure astrom produced by this function is used by iauAtioq, iauAtoiq, iauAtciq* and iauAticq*.

Called:

   iauUtctai    UTC to TAI
   iauTaitt     TAI to TT
   iauUtcut1    UTC to UT1
   iauEpv00     Earth position and velocity
   iauPnm06a    classical NPB matrix, IAU 2006/2000A
   iauBpn2xy    extract CIP X,Y coordinates from NPB matrix
   iauS06       the CIO locator s, given X,Y, IAU 2006
   iauEra00     Earth rotation angle, IAU 2000
   iauSp00      the TIO locator s', IERS 2000
   iauRefco     refraction constants for given ambient conditions
   iauApco      astrometry parameters, ICRS-observed
   iauEors      equation of the origins, given NPB matrix and s

apco13

Function apco13 Copy item path

Function apco13