apco13¶
- erfa.apco13(utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)[source]¶
For a terrestrial observer, prepare star-independent astrometry parameters for transformations between ICRS and observed coordinates.
- Parameters:
- utc1double array
- utc2double array
- dut1double array
- elongdouble array
- phidouble array
- hmdouble array
- xpdouble array
- ypdouble array
- phpadouble array
- tcdouble array
- rhdouble array
- wldouble array
- Returns:
- astromeraASTROM array
- eodouble array
Notes
Wraps ERFA function
eraApco13
. The ERFA documentation is:- - - - - - - - - - e r a A p c o 1 3 - - - - - - - - - - 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 ERFA 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. 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 eraASTROM* 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: 1) 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 eraDtf2d 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. 2) 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 eraDat for further details. 3) 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. 4) The geographical coordinates are with respect to the ERFA_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. 5) 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. 6) 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. 7) 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). 8) 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. 9) In cases where the caller wishes to supply his own Earth ephemeris, Earth rotation information and refraction constants, the function eraApco can be used instead of the present function. 10) 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 eraApcg eraApcg13 geocentric ICRS <-> GCRS eraApci eraApci13 terrestrial ICRS <-> CIRS eraApco eraApco13 terrestrial ICRS <-> observed eraApcs eraApcs13 space ICRS <-> GCRS eraAper eraAper13 terrestrial update Earth rotation eraApio eraApio13 terrestrial CIRS <-> observed Those with names ending in "13" use contemporary ERFA 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. 11) The context structure astrom produced by this function is used by eraAtioq, eraAtoiq, eraAtciq* and eraAticq*. Called: eraUtctai UTC to TAI eraTaitt TAI to TT eraUtcut1 UTC to UT1 eraEpv00 Earth position and velocity eraPnm06a classical NPB matrix, IAU 2006/2000A eraBpn2xy extract CIP X,Y coordinates from NPB matrix eraS06 the CIO locator s, given X,Y, IAU 2006 eraEra00 Earth rotation angle, IAU 2000 eraSp00 the TIO locator s', IERS 2000 eraRefco refraction constants for given ambient conditions eraApco astrometry parameters, ICRS-observed eraEors equation of the origins, given NPB matrix and s This revision: 2022 May 3 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.