cspice_srfxpt |
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## AbstractCSPICE_SRFXPT computes the surface intercept point of a specified ray on a target body at a specified epoch, optionally corrected for light time and stellar aberration, given an observer and a direction vector defining a ray. Deprecated: This routine has been superseded by the routine cspice_sincpt. This routine is supported for purposes of backward compatibility only. ## I/OGiven: method a string providing parameters defining the computation method to use. [1,c1] = size(method); char = class(method) or [1,1] = size(method); cell = class(method) The only currently supported choice: "Ellipsoid" The intercept computation uses a triaxial ellipsoid to model the surface of the target body. The ellipsoid's radii must be available in the kernel pool. Neither case nor white space are significant in 'method'. target the name of the target body. The target body is an ephemeris object (its trajectory is given by SPK data), and is an extended object. Optionally, you may supply the integer ID code for the object as an integer string, i.e. both 'MOON' and '301' are legitimate strings that indicate the Moon is the target body. [1,c2] = size(target); char = class(target) or [1,1] = size(target); cell = class(target) et the ephemeris time(s), expressed as seconds past J2000 TDB, at which to compute the surface intercept point on the target body (this epoch represents either the time of signal reception, or transmission, depending on the selected 'abcorr') [1,n] = size(et); double = class(et) abcorr the aberration correction to apply when computing the observer-target state and the target body orientation. [1,c3] = size(abcorr); char = class(abcorr) or [1,1] = size(abcorr); cell = class(abcorr) For practical purposes, 'CN' (converged Newtonian) represents the best correction choice. 'abcorr' may be any of the following: 'NONE' Apply no correction. Return the geometric surface intercept point on the target body. Let 'lt' represent the one-way light time between the observer and the surface intercept point (note: NOT between the observer and the target body's center). The following values of 'abcorr' apply to the "reception" case in which photons depart from the intercept point's location at the light-time corrected epoch et-lt and *arrive* at the observer's location at 'et': 'LT' Correct for one-way light time (also called "planetary aberration") using a Newtonian formulation. This correction yields the location of the surface intercept point at the moment it emitted photons arriving at the observer at 'et'. The light time correction uses an iterative solution of the light time equation. The solution invoked by the 'LT' option uses one iteration. Both the target state as seen by the observer, and rotation of the target body, are corrected for light time. 'LT+S' Correct for one-way light time and stellar aberration using a Newtonian formulation. This option modifies the state obtained with the 'LT' option to account for the observer's velocity relative to the solar system barycenter. The result is the apparent surface intercept point as seen by the observer. 'CN' Converged Newtonian light time correction. In solving the light time equation, the 'CN' correction iterates until the solution converges. Both the state and rotation of the target body are corrected for light time. 'CN+S' Converged Newtonian light time and stellar aberration corrections. The following values of 'abcorr' apply to the "transmission" case in which photons *depart* from the observer's location at 'et' and arrive at the intercept point at the light-time corrected epoch et+lt: 'XLT' "Transmission" case: correct for one-way light time using a Newtonian formulation. This correction yields the intercept location at the moment it receives photons emitted from the observer's location at 'et'. The light time correction uses an iterative solution of the light time equation. The solution invoked by the 'LT' option uses one iteration. Both the target state as seen by the observer, and rotation of the target body, are corrected for light time. 'XLT+S' "Transmission" case: correct for one-way light time and stellar aberration using a Newtonian formulation This option modifies the intercept obtained with the 'XLT' option to account for the observer's velocity relative to the solar system barycenter. 'XCN' Converged Newtonian light time correction. This is the same as 'XLT' correction but with further iterations to a converged Newtonian light time solution. 'XCN+S' "Transmission" case: converged Newtonian light time and stellar aberration corrections. obsrvr the name of a observing body. Optionally, you may supply the integer ID code for the object as an integer string, i.e. both 'MOON' and '301' are legitimate strings that indicate the Moon is the observing body. [1,c4] = size(obsrvr); char = class(obsrvr) or [1,1] = size(obsrvr); cell = class(obsrvr) dref the name of the reference frame relative to which the input direction vector is expressed. This may be any frame supported by the SPICE system, including built-in frames (documented in the Frames Required Reading) and frames defined by a loaded frame kernel (FK). [1,c5] = size(dref); char = class(dref) or [1,1] = size(dref); cell = class(dref) When 'dref' designates a non-inertial frame, the orientation of the frame is evaluated at an epoch dependent on the frame's center and, if the center is not the observer, on the selected aberration correction. See the description of the direction vector 'dvec' for details. dvec Pointing vector emanating from the observer. The intercept with the target body's surface of the ray defined by the observer and 'dvec' is sought. [3,1] = size(dvec); double = class(dvec) 'dvec' is specified relative to the reference frame designated by 'dref'. Non-inertial reference frames are treated as follows: if the center of the frame is at the observer's location, the frame is evaluated at 'et'. If the frame's center is located elsewhere, then letting 'ltcent' be the one-way light time between the observer and the central body associated with the frame, the orientation of the frame is evaluated at et-ltcent, et+ltcent, or 'et' depending on whether the requested aberration correction is, respectively, for received radiation, transmitted radiation, or is omitted. 'ltcent' is computed using the method indicated by 'abcorr'. the call: [ spoint, dist, trgepc, obspos, found ] = ... ## ExamplesAny numerical results shown for this example may differ between platforms as the results depend on the SPICE kernels used as input and the machine specific arithmetic implementation. % % Assign needed constants. % BUSID = -94000; MGS = -94; NCORNR = 4; ABCORR = 'LT+S'; CAMERA = 'MGS_MOC_NA'; DREF = 'J2000'; METHOD = 'ELLIPSOID'; OBSRVR = 'MGS'; TARGET = 'MARS'; UTC = '2003 OCT 13 06:00:00 UTC'; % % Load kernel files: % % - Leapseconds kernel % - MGS SCLK kernel % - Text PCK file % - Planetary SPK file % - MGS I-kernel % - MGS spacecraft bus C-kernel % - MGS SPK file % cspice_furnsh( '/kernels/gen/lsk/naif0008.tls' ) cspice_furnsh( '/kernels/MGS/sclk/MGS_SCLKSCET.00053.tsc' ) cspice_furnsh( '/kernels/MGS/pck/mars_iau2000_v0.tpc' ) cspice_furnsh( '/kernels/gen/spk/de405s.bsp' ) cspice_furnsh( '/kernels/MGS/ik/moc20.ti' ) cspice_furnsh( '/kernels/MGS/ck/mgs_sc_ext12.bc' ) cspice_furnsh( '/kernels/MGS/spk/mgs_ext12.bsp' ) % % Convert the UTC request time to ET (seconds past % J2000, TDB). % et = cspice_str2et( UTC ); % % Get the MGS MOC Narrow angle camera (MGS_MOC_NA) % ID code. Then look up the field of view (FOV) % parameters. % [camid, found] = cspice_bodn2c( CAMERA ); [shape, dref, bsight, bounds] = cspice_getfov( camid, NCORNR); disp( ' ' ) disp( 'Surface Intercept Locations for Camera' ) disp( 'FOV Boundary and Boresight Vectors' ) disp( ' ' ) txt = sprintf( ' Instrument: %s', CAMERA); disp( txt ) txt = sprintf( ' Epoch: %s', UTC); disp( txt ) txt = sprintf( ' Aberration correction: %s', ABCORR); disp( txt ) disp( ' ' ) % % Now compute and display the surface intercepts for the % boresight and all of the FOV boundary vectors. % for i=1:NCORNR+1 if( i <= NCORNR ) % % 'bounds' represents a 3 X NCORNR array with each row a bounds % vector. Extract the vectors from 'bounds' using as a vector % segment. % % corner vector 0: bounds(:,1) % corner vector 1: bounds(:,2) % corner vector 2: bounds(:,3) % corner vector 3: bounds(:,4) % % title = sprintf( 'Corner vector %d', i ); dvec = bounds(:,i); else title = sprintf( 'Boresight vector' ); dvec = bsight; end % % Compute the surface intercept point using % the specified aberration corrections. % [spoint, dist, trgepc, obspos, found] = ... ## ParticularsA sister version of this routine exists named mice_srfxpt that returns the output arguments as fields in a single structure. ## Required ReadingFor important details concerning this module's function, please refer to the CSPICE routine srfxpt_c. MICE.REQ FRAMES.REQ NAIF_IDS.REQ PCK.REQ SPK.REQ TIME.REQ ## Version-Mice Version 1.0.3, 12-FEB-2015, EDW (JPL) Edited I/O section to conform to NAIF standard for Mice documentation. -Mice Version 1.0.2, 18-MAY-2010, BVS (JPL) Index line now states that this routine is deprecated. -Mice Version 1.0.1, 11-NOV-2008, EDW (JPL) Edits to header; Abstract now states that this routine is deprecated. -Mice Version 1.0.0, 03-JAN-2006, EDW (JPL) ## Index_EntriesDEPRECATED surface intercept point |

Wed Apr 5 18:00:35 2017