void eraC2i00b(double date1, double date2, double rc2i[3][3]) /* ** - - - - - - - - - - ** e r a C 2 i 0 0 b ** - - - - - - - - - - ** ** Form the celestial-to-intermediate matrix for a given date using the ** IAU 2000B precession-nutation model. ** ** Given: ** date1,date2 double TT as a 2-part Julian Date (Note 1) ** ** Returned: ** rc2i double[3][3] celestial-to-intermediate matrix (Note 2) ** ** Notes: ** ** 1) The TT date date1+date2 is a Julian Date, apportioned in any ** convenient way between the two arguments. For example, ** JD(TT)=2450123.7 could be expressed in any of these ways, ** among others: ** ** date1 date2 ** ** 2450123.7 0.0 (JD method) ** 2451545.0 -1421.3 (J2000 method) ** 2400000.5 50123.2 (MJD method) ** 2450123.5 0.2 (date & time method) ** ** The JD method is the most natural and convenient to use in ** cases where the loss of several decimal digits of resolution ** is acceptable. The J2000 method is best matched to the way ** the argument is handled internally and will deliver the ** optimum resolution. The MJD method and the date & time methods ** are both good compromises between resolution and convenience. ** ** 2) The matrix rc2i is the first stage in the transformation from ** celestial to terrestrial coordinates: ** ** [TRS] = RPOM * R_3(ERA) * rc2i * [CRS] ** ** = rc2t * [CRS] ** ** where [CRS] is a vector in the Geocentric Celestial Reference ** System and [TRS] is a vector in the International Terrestrial ** Reference System (see IERS Conventions 2003), ERA is the Earth ** Rotation Angle and RPOM is the polar motion matrix. ** ** 3) The present function is faster, but slightly less accurate (about ** 1 mas), than the eraC2i00a function. ** ** Called: ** eraPnm00b classical NPB matrix, IAU 2000B ** eraC2ibpn celestial-to-intermediate matrix, given NPB matrix ** ** References: ** ** "Expressions for the Celestial Intermediate Pole and Celestial ** Ephemeris Origin consistent with the IAU 2000A precession- ** nutation model", Astron.Astrophys. 400, 1145-1154 ** (2003) ** ** n.b. The celestial ephemeris origin (CEO) was renamed "celestial ** intermediate origin" (CIO) by IAU 2006 Resolution 2. ** ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), ** IERS Technical Note No. 32, BKG (2004) ** ** Copyright (C) 2013, NumFOCUS Foundation. ** Derived, with permission, from the SOFA library. See notes at end of file. */ { double rbpn[3][3]; /* Obtain the celestial-to-true matrix (IAU 2000B). */ eraPnm00b(date1, date2, rbpn); /* Form the celestial-to-intermediate matrix. */ eraC2ibpn(date1, date2, rbpn, rc2i); return; }
void eraXys00b(double date1, double date2, double *x, double *y, double *s) /* ** - - - - - - - - - - ** e r a X y s 0 0 b ** - - - - - - - - - - ** ** For a given TT date, compute the X,Y coordinates of the Celestial ** Intermediate Pole and the CIO locator s, using the IAU 2000B ** precession-nutation model. ** ** Given: ** date1,date2 double TT as a 2-part Julian Date (Note 1) ** ** Returned: ** x,y double Celestial Intermediate Pole (Note 2) ** s double the CIO locator s (Note 2) ** ** Notes: ** ** 1) The TT date date1+date2 is a Julian Date, apportioned in any ** convenient way between the two arguments. For example, ** JD(TT)=2450123.7 could be expressed in any of these ways, ** among others: ** ** date1 date2 ** ** 2450123.7 0.0 (JD method) ** 2451545.0 -1421.3 (J2000 method) ** 2400000.5 50123.2 (MJD method) ** 2450123.5 0.2 (date & time method) ** ** The JD method is the most natural and convenient to use in ** cases where the loss of several decimal digits of resolution ** is acceptable. The J2000 method is best matched to the way ** the argument is handled internally and will deliver the ** optimum resolution. The MJD method and the date & time methods ** are both good compromises between resolution and convenience. ** ** 2) The Celestial Intermediate Pole coordinates are the x,y ** components of the unit vector in the Geocentric Celestial ** Reference System. ** ** 3) The CIO locator s (in radians) positions the Celestial ** Intermediate Origin on the equator of the CIP. ** ** 4) The present function is faster, but slightly less accurate (about ** 1 mas in X,Y), than the eraXys00a function. ** ** Called: ** eraPnm00b classical NPB matrix, IAU 2000B ** eraBpn2xy extract CIP X,Y coordinates from NPB matrix ** eraS00 the CIO locator s, given X,Y, IAU 2000A ** ** Reference: ** ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), ** IERS Technical Note No. 32, BKG (2004) ** ** Copyright (C) 2013-2016, NumFOCUS Foundation. ** Derived, with permission, from the SOFA library. See notes at end of file. */ { double rbpn[3][3]; /* Form the bias-precession-nutation matrix, IAU 2000A. */ eraPnm00b(date1, date2, rbpn); /* Extract X,Y. */ eraBpn2xy(rbpn, x, y); /* Obtain s. */ *s = eraS00(date1, date2, *x, *y); return; }
double eraS00b(double date1, double date2) /* ** - - - - - - - - ** e r a S 0 0 b ** - - - - - - - - ** ** The CIO locator s, positioning the Celestial Intermediate Origin on ** the equator of the Celestial Intermediate Pole, using the IAU 2000B ** precession-nutation model. ** ** Given: ** date1,date2 double TT as a 2-part Julian Date (Note 1) ** ** Returned (function value): ** double the CIO locator s in radians (Note 2) ** ** Notes: ** ** 1) The TT date date1+date2 is a Julian Date, apportioned in any ** convenient way between the two arguments. For example, ** JD(TT)=2450123.7 could be expressed in any of these ways, ** among others: ** ** date1 date2 ** ** 2450123.7 0.0 (JD method) ** 2451545.0 -1421.3 (J2000 method) ** 2400000.5 50123.2 (MJD method) ** 2450123.5 0.2 (date & time method) ** ** The JD method is the most natural and convenient to use in ** cases where the loss of several decimal digits of resolution ** is acceptable. The J2000 method is best matched to the way ** the argument is handled internally and will deliver the ** optimum resolution. The MJD method and the date & time methods ** are both good compromises between resolution and convenience. ** ** 2) The CIO locator s is the difference between the right ascensions ** of the same point in two systems. The two systems are the GCRS ** and the CIP,CIO, and the point is the ascending node of the ** CIP equator. The CIO locator s remains a small fraction of ** 1 arcsecond throughout 1900-2100. ** ** 3) The series used to compute s is in fact for s+XY/2, where X and Y ** are the x and y components of the CIP unit vector; this series ** is more compact than a direct series for s would be. The present ** function uses the IAU 2000B truncated nutation model when ** predicting the CIP position. The function eraS00a uses instead ** the full IAU 2000A model, but with no significant increase in ** accuracy and at some cost in speed. ** ** Called: ** eraPnm00b classical NPB matrix, IAU 2000B ** eraBnp2xy extract CIP X,Y from the BPN matrix ** eraS00 the CIO locator s, given X,Y, IAU 2000A ** ** References: ** ** Capitaine, N., Chapront, J., Lambert, S. and Wallace, P., ** "Expressions for the Celestial Intermediate Pole and Celestial ** Ephemeris Origin consistent with the IAU 2000A precession- ** nutation model", Astron.Astrophys. 400, 1145-1154 (2003) ** ** n.b. The celestial ephemeris origin (CEO) was renamed "celestial ** intermediate origin" (CIO) by IAU 2006 Resolution 2. ** ** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), ** IERS Technical Note No. 32, BKG (2004) ** ** Copyright (C) 2013, NumFOCUS Foundation. ** Derived, with permission, from the SOFA library. See notes at end of file. */ { double rbpn[3][3], x, y, s; /* Bias-precession-nutation-matrix, IAU 2000B. */ eraPnm00b(date1, date2, rbpn); /* Extract the CIP coordinates. */ eraBpn2xy(rbpn, &x, &y); /* Compute the CIO locator s, given the CIP coordinates. */ s = eraS00(date1, date2, x, y); return s; }