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: http://www.stsci.edu/~sontag/spicedocs/cspice/srfrec_c.html
Дата изменения: Sat Dec 17 06:09:53 2005 Дата индексирования: Mon Apr 11 00:11:02 2016 Кодировка: Поисковые слова: molecules |
Convert planetocentric latitude and longitude of a surface point on a specified body to rectangular coordinates.
KERNEL NAIF_IDS
Variable I/O Description -------- --- -------------------------------------------------- body I NAIF integer code of an extended body. longitude I Longitude of point in radians. latitude I Latitude of point in radians. rectan O Rectangular coordinates of the point.
body 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. longitude Longitude of the input point. This is the angle between the prime meridian and the meridian containing `rectan'. 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. latitude 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.
rectan The rectangular coordinates of the input point. `rectan' is a 3-vector. Units are the same as those used to define the radii of `body'. Normally, these units are km.
None.
This 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, longitude and latitude ) 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 longitude latitude 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.
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. #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 srfrec_c. ./ srfrec_c ( EARTH, lon*rpd_c(), lat*rpd_c(), x ); printf ( "\n" "Rectangular coordinates:\n" "\n" "X (km): %24.16f\n" "Y (km): %24.16f\n" "Z (km): %25.16f\n", x[0], x[1], x[2] ); /. Now try to recover the original latitudinal coordinates from the rectangular coordinates found by srfrec_c. ./ reclat_c ( x, &radius, &lon, &lat ); /. Convert angles back to degree for display. ./ printf ( "\n" "Latitudinal coordinates recovered from " "rectangular coordinates:\n" "\n" "Longitude (deg): %f\n" "Latitude (deg): %f\n" "Radius (km): %f\n", lon * dpr_c(), lat * dpr_c(), radius ); return ( 0 ); }
1) A SPICE 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.
1) If radii for `body' are not found in the kernel pool, the error will be diagnosed by routines called by this routine. 2) If radii for `body' are invalid, the error will be diagnosed by routines called by this routine. The radii should be positive.
None.
N.J. Bachman (JPL) W.L. Taber (JPL)
None.
-CSPICE Version 1.0.0, 03-NOV-2005 (NJB) (WLT)
convert bodyfixed latitudinal coordinates to rectangular convert surface latitudinal coordinates to rectangular surface point latitudinal coordinates to rectangular