stelab_c |

Table of contents## Procedurestelab_c ( Stellar Aberration ) void stelab_c ( ConstSpiceDouble pobj[3], ConstSpiceDouble vobs[3], SpiceDouble appobj[3] ) ## AbstractCorrect the apparent position of an object for stellar aberration. ## Required_ReadingNone. ## KeywordsEPHEMERIS ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- pobj I Position of an object with respect to the observer. vobs I Velocity of the observer with respect to the Solar System barycenter. appobj O Apparent position of the object with respect to the observer, corrected for stellar aberration. ## Detailed_Inputpobj is the position (x, y, z, km) of an object with respect to the observer, possibly corrected for light time. vobs is the velocity (dx/dt, dy/dt, dz/dt, km/sec) of the observer with respect to the Solar System barycenter. ## Detailed_Outputappobj is the apparent position of the object relative to the observer, corrected for stellar aberration. ## ParametersNone. ## Exceptions1) If the velocity of the observer is greater than or equal to the speed of light, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. ## FilesNone. ## ParticularsLet r be the vector from the observer to the object, and v be - - the velocity of the observer with respect to the Solar System barycenter. Let w be the angle between them. The aberration angle phi is given by sin(phi) = v sin(w) / c Let h be the vector given by the cross product - h = r X v - - - Rotate r by phi radians about h to obtain the apparent position - - of the object. ## ExamplesThe numerical results shown for this example may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation. 1) Compute the apparent position of the Moon relative to the Earth, corrected for one light-time and stellar aberration, given the geometric state of the Earth relative to the Solar System Barycenter, and the difference between the stellar aberration corrected and uncorrected position vectors, taking several steps. First, compute the light-time corrected state of the Moon body as seen by the Earth, using its geometric state. Then apply the correction for stellar aberration to the light-time corrected state of the target body. The code in this example could be replaced by a single call to spkpos_c: spkpos_c ( "MOON", et, "J2000", "LT+S", "EARTH", pos, < ); Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File name: stelab_ex1.tm This meta-kernel is intended to support operation of SPICE example programs. The kernels shown here should not be assumed to contain adequate or correct versions of data required by SPICE-based user applications. In order for an application to use this meta-kernel, the kernels referenced here must be present in the user's current working directory. The names and contents of the kernels referenced by this meta-kernel are as follows: File name Contents --------- -------- de418.bsp Planetary ephemeris naif0009.tls Leapseconds \begindata KERNELS_TO_LOAD = ( 'de418.bsp', 'naif0009.tls' ) \begintext End of meta-kernel Example code begins here. /. Program stelab_ex1 ./ #include <stdio.h> #include "SpiceUsr.h" int main () { /. Local variables. ./ SpiceChar * reffrm; SpiceChar * utcstr; SpiceDouble appdif [ 3 ]; SpiceDouble et; SpiceDouble lt; SpiceDouble pcorr [ 3 ]; SpiceDouble pos [ 3 ]; SpiceDouble sobs [ 6 ]; SpiceInt idobs; SpiceInt idtarg; /. Assign an observer, Earth, target, Moon, time of interest and reference frame for returned vectors. ./ idobs = 399; idtarg = 301; utcstr = "July 4 2004"; reffrm = "J2000"; /. Load the needed kernels. ./ furnsh_c ( "stelab_ex1.tm" ); /. Convert the time string to ephemeris time, J2000. ./ str2et_c ( utcstr, &et ); /. Get the state of the observer with respect to the solar system barycenter. ./ spkssb_c ( idobs, et, reffrm, sobs ); /. Get the light-time corrected position `pos' of the target body `idtarg' as seen by the observer. ./ spkapo_c ( idtarg, et, reffrm, sobs, "LT", pos, < ); /. Output the uncorrected vector. ./ printf ( "Uncorrected position vector\n" ); printf ( " %18.6f %18.6f %18.6f\n", pos[0], pos[1], pos[2] ); /. Apply the correction for stellar aberration to the light-time corrected position of the target body. ./ ## RestrictionsNone. ## Literature_References[1] W. Owen, "The Treatment of Aberration in Optical Navigation", JPL IOM #314.8-524, 8 February 1985. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) W.L. Taber (JPL) I.M. Underwood (JPL) ## Version-CSPICE Version 1.0.2, 05-JUL-2021 (JDR) Edited the header to comply with NAIF standard. Added example's meta-kernel and problem statement. Created complete code example from existing code fragments. -CSPICE Version 1.0.1, 08-JAN-2008 (NJB) The header example was updated to remove references to spkapp_c. -CSPICE Version 1.0.0, 22-OCT-1998 (NJB) (IMU) (WLT) Based on SPICELIB Version 1.0.2, 10-MAR-1992 (WLT) ## Index_Entriesstellar aberration |

Fri Dec 31 18:41:13 2021