srfrec_c |

Table of contents## Proceduresrfrec_c ( Surface to rectangular coordinates ) void srfrec_c ( SpiceInt body, SpiceDouble lon, SpiceDouble lat, SpiceDouble rectan[3] ) ## AbstractConvert planetocentric latitude and longitude of a surface point on a specified body to rectangular coordinates. ## Required_ReadingKERNEL NAIF_IDS ## KeywordsCONVERSION COORDINATES TRANSFORMATION ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- body I NAIF integer code of an extended body. lon I Longitude of point in radians. lat I Latitude of point in radians. rectan O Rectangular coordinates of the point. ## Detailed_Inputbody is the NAIF integer code of an extended body on which a surface point of interest is located. The body is modeled as a triaxial ellipsoid. lon is the longitude of the input point. This is the angle between the prime meridian and the meridian containing the point. The direction of increasing longitude is from the +X axis towards the +Y axis. Longitude is measured in radians. On input, the range of longitude is unrestricted. lat is the latitude of the input point. This is the angle from the XY plane of the ray from the origin through the point. Latitude is measured in radians. On input, the range of latitude is unrestricted. ## Detailed_Outputrectan are the rectangular coordinates of the input surface point. `rectan' is a 3-vector. Units are the same as those used to define the radii of `body'. Normally, these units are km. ## ParametersNone. ## Exceptions1) If radii for `body' are not found in the kernel pool, an error is signaled by a routine in the call tree of this routine. 2) If the size of the `body' body radii kernel variable is not three, an error is signaled by a routine in the call tree of this routine. 3) If any of the three `body' body radii is less-than or equal to zero, an error is signaled by a routine in the call tree of this routine. ## FilesNone. ## ParticularsThis routine returns the rectangular coordinates of a surface point on an extended body with known radii, where the location of the surface point is specified in planetocentric latitudinal coordinates. Latitudinal coordinates are defined by a distance from a central reference point, an angle from a reference meridian, and an angle above the equator of a sphere centered at the central reference point. In this case, the distance from the central reference point is not required as an input because the fact that the point is on the body's surface allows one to deduce this quantity. Below are two tables that demonstrate by example the relationship between rectangular and latitudinal coordinates. Listed in the first table (under R, `lon' and `lat') are latitudinal coordinate triples that approximately represent points whose rectangular coordinates are taken from the set {-1, 0, 1}. (Angular quantities are given in degrees.) R lon lat rectan[0] rectan[1] rectan[2] -------------------------- -------------------------------- 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 1.0000 0.0000 0.0000 1.0000 0.0000 0.0000 1.0000 90.0000 0.0000 0.0000 1.0000 0.0000 1.0000 0.0000 90.0000 0.0000 0.0000 1.0000 1.0000 180.0000 0.0000 -1.0000 0.0000 0.0000 1.0000 -90.0000 0.0000 0.0000 -1.0000 0.0000 1.0000 0.0000 -90.0000 0.0000 0.0000 -1.0000 1.4142 45.0000 0.0000 1.0000 1.0000 0.0000 1.4142 0.0000 45.0000 1.0000 0.0000 1.0000 1.4142 90.0000 45.0000 0.0000 1.0000 1.0000 1.7320 45.0000 35.2643 1.0000 1.0000 1.0000 This routine is related to the CSPICE routine latrec_c, which accepts a radius, longitude, and latitude as inputs and produces equivalent rectangular coordinates as outputs. ## 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) Find the rectangular coordinates of the point 100 degrees planetocentric longitude -35 degrees planetocentric latitude on the Earth; then convert these coordinates back to latitudinal coordinates. We should be able to recover our original longitude and latitude values. Use the PCK kernel below to load the required triaxial ellipsoidal shape model and orientation data for the Earth. pck00008.tpc Example code begins here. /. Program srfrec_ex1 ./ #include <stdio.h> #include "SpiceUsr.h" int main() { #define EARTH 399 SpiceDouble lat; SpiceDouble lon; SpiceDouble x [3]; SpiceDouble radius; /. Load the kernel pool with a PCK file that contains values for the radii of the Earth. ./ furnsh_c ( "pck00008.tpc" ); /. Find `x', the rectangular coordinates of the surface point defined by `lat' and `long'. The NAIF integer code for the Earth is 399. (See the NAIF_IDS required reading file for the complete set of codes.) ./ lon = 100.0; lat = -35.0; printf ( "Original latitudinal coordinates\n" "\n" " Longitude (deg) = %f\n" " Latitude (deg) = %f\n", lon, lat ); /. Convert angles to radians forr input to ## Restrictions1) A PCK text kernel containing the body radius definitions required by this routine must be loaded into the kernel pool prior to any calls to this routine. ## Literature_ReferencesNone. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) W.L. Taber (JPL) ## Version-CSPICE Version 1.1.0, 01-NOV-2021 (JDR) Changed the input argument names "longitude" and "latitude" by "lon and "lat" for consistency with other routines. Edited the header to comply with NAIF standard. Modified code example output format. Added solutions to the -Examples section. -CSPICE Version 1.0.0, 03-NOV-2005 (NJB) (WLT) ## Index_Entriesconvert body-fixed latitudinal coordinates to rectangular convert surface latitudinal coordinates to rectangular surface point latitudinal coordinates to rectangular |

Fri Dec 31 18:41:13 2021