Index Page xfmsta_c

A B C D E F G H I J K L M N O P Q R S T U V W X

Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

       void xfmsta_c ( ConstSpiceDouble     input_state[6],
                       ConstSpiceChar     * input_coord_sys,
                       ConstSpiceChar     * output_coord_sys,
                       ConstSpiceChar     * body,
                       SpiceDouble          output_state[6]  )

#### Abstract

       Transform a state between coordinate systems.

#### Required_Reading

       None.

#### Keywords

       CONVERSION
       COORDINATE
       EPHEMERIS
       STATE

#### Brief_I/O

       VARIABLE         I/O  DESCRIPTION
       --------         ---  -------------------------------------------
       input_state       I   Input state.
       input_coord_sys   I   Current (input) coordinate system.
       output_coord_sys  I   Desired (output) coordinate system.
       body              I   Name or NAIF ID of body with which
                             coordinates are associated (if applicable).
       output_state      O   Converted output state.

#### Detailed_Input

       input_state       is a state vector in the input (`input_coord_sys')
                         coordinate system representing position and velocity.

                         All angular measurements must be in radians.

                         Note: body radii values taken from the kernel
                         pool are used when converting to or from geodetic or
                         planetographic coordinates. It is the user's
                         responsibility to verify the distance inputs are in
                         the same units as the radii in the kernel pool,
                         typically kilometers.

       input_coord_sys   is the name of the coordinate system that the input
                         state vector (`input_state') is currently in.

                         `input_coord_sys' may be any of the following:

                               'RECTANGULAR'
                               'CYLINDRICAL'
                               'LATITUDINAL'
                               'SPHERICAL'
                               'GEODETIC'
                               'PLANETOGRAPHIC'

                         Leading spaces, trailing spaces, and letter case
                         are ignored. For example, ' cyLindRical  ' would
                         be accepted.

       output_coord_sys  is the name of the coordinate system that the state
                         should be converted to.

                         Please see the description of `input_coord_sys'
                         for details.

       body              is the name or NAIF ID of the body associated with the
                         planetographic or geodetic coordinate system.

                         If neither of the coordinate system choices are
                         geodetic or planetographic, `body' may be an empty
                         string (' ').

                         Examples of accepted body names or IDs are:
                                  'Earth'
                                  '399'

                         Leading spaces, trailing spaces, and letter case are
                         ignored.

#### Detailed_Output

       output_state      is the state vector that has been converted to the
                         output coordinate system (`output_coord_sys').

#### Parameters

       None.

#### Exceptions

       1)  If either the input or output coordinate system is not
           recognized, the error SPICE(COORDSYSNOTREC) is signaled.

       2)  If the input body name cannot be converted to a NAIF ID
           (applies to geodetic and planetographic coordinate
           systems), the error 'SPICE(IDCODENOTFOUND)' is signaled.

       3)  If the input state `input_state' is not valid, meaning the position
           but not the velocity is along the z-axis, the error
           'SPICE(INVALIDSTATE)' is signaled.

           Note: If both the input position and velocity are along
           the z-axis and the output coordinate system is not
           rectangular, the velocity can still be calculated even
           though the Jacobian is undefined. This case will not
           signal an error. An example of the input position and
           velocity along the z-axis is below.

                         Term    Value
                         -----   ------
                           x       0
                           y       0
                           z       z
                         dx/dt     0
                         dy/dt     0
                         dz/dt   dz_dt

       4)  If either the input or output coordinate system is
           geodetic or planetographic and at least one of the body's
           radii is less than or equal to zero, the error
           SPICE(INVALIDRADIUS) will be signaled.

       5)  If either the input or output coordinate system is
           geodetic or planetographic and the difference of the
           equatorial and polar radii divided by the equatorial radius
           would produce numeric overflow, the error
           'SPICE(INVALIDRADIUS)' will be signaled.

       6)  If the product of the Jacobian and velocity components
           may lead to numeric overflow, the error 'SPICE(NUMERICOVERFLOW)'
           is signaled.

       7)  If body's equatorial radii are not equal and either the
           input or output coordinate system is geodetic or
           planetographic, the error 'SPICE(NOTSUPPORTED)' is signaled.

#### Files

       SPK, PCK, CK, and FK kernels may be required.

       If the input or output coordinate systems are either geodetic or
       planetographic, a PCK providing the radii of the body
       name `body' must be loaded via furnsh_c.

       Kernel data are normally loaded once per program run, NOT every
       time this routine is called.

#### Particulars

       Input Order
       -------------------------------------------

          The input and output states will be structured by the
          following descriptions.

          For rectangular coordinates, the state vector is the following
          in which X, Y, and Z are the rectangular position components and
          DX, DY, and DZ are the time derivatives of each position component.
                  ISTATE = ( X, Y, Z, DX, DY, DZ )

          For cylindrical coordinates, the state vector is the following
          in which R is the radius, LONG is the longitude, Z is the
          height, and DR, DLONG, and DZ are the time derivatives of each
          position component.
                  ISTATE = ( R, LONG, Z, DR, DLONG, DZ )

          For latitudinal coordinates, the state vector is the following
          in which R is the radius, LONG is the longitude, LAT is the
          latitude, and DR, DLONG, and DLAT are the time derivatives of
          each position component.
                  ISTATE = ( R, LONG, LAT, DR, DLONG, DLAT )

          For spherical coordinates, the state vector is the following in
          which R is the radius, COLAT is the colatitude, LONG is the
          longitude, and DR, DCOLAT, and DLONG are the time derivatives of
          each position component.
                  ISTATE = ( R, COLAT, LONG, DR, DCOLAT, DLONG )

          For geodetic coordinates, the state vector is the following in
          which LONG is the longitude, LAT is the latitude, ALT is the
          altitude, and DLONG, DLAT, and DALT are the time derivatives of
          each position component.
                  ISTATE = ( LONG, LAT, ALT, DLONG, DLAT, DALT )

          For planetographic coordinates, the state vector is the
          following in which LONG is the longitude, LAT is the latitude,
          ALT is the altitude, and DLONG, DLAT, and DALT are the time
          derivatives of each position component.
                  ISTATE = ( LONG, LAT, ALT, DLONG, DLAT, DALT )

       Input Boundaries
       -------------------------------------------

          There are intervals the input angles must fall within if
          the input coordinate system is not rectangular. These
          intervals are provided below.

             Input variable    Input meaning   Input interval [rad]
             --------------    -------------   ------------------------
                 LONG           Longitude        0     <= LONG  <  2*pi
                 LAT            Latitude        -pi/2  <= LAT   <= pi/2
                 COLAT          Colatitude       0     <= COLAT <= pi

#### Examples

       The numerical results shown for these examples 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 apparent state of Phoebe as seen by CASSINI in the
          J2000 frame at 2004 Jun 11 19:32:00. Transform the state
          from rectangular to latitudinal coordinates. For verification,
          transform the state back from latitudinal to rectangular
          coordinates.

          Use the meta-kernel shown below to load the required SPICE
          kernels.

             KPL/MK

             File name: xfmsta_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
                    ---------                     --------
                    cpck05Mar2004.tpc             Planet orientation and
                                                  radii
                    naif0009.tls                  Leapseconds
                    020514_SE_SAT105.bsp          Satellite ephemeris for
                                                  Saturn
                    030201AP_SK_SM546_T45.bsp     CASSINI ephemeris
                    981005_PLTEPH-DE405S.bsp      Planetary ephemeris

             \begindata

             KERNELS_TO_LOAD = ( 'naif0009.tls'  ,
                                 '020514_SE_SAT105.bsp'  ,
                                 '030201AP_SK_SM546_T45.bsp'  ,
                                 '981005_PLTEPH-DE405S.bsp',
                                 'cpck05Mar2004.tpc'   )

             End of meta-kernel

          Example code begins here.

             #include <stdio.h>
             #include "SpiceUsr.h"

             int main()
             {

                /.
                Constants
                ./

                #define METAKR "xfmsta_ex1.tm"

                /.
                Local variables

                `et' is the ephemeris time (TDB) corresponding to the
                observation.
                ./
                SpiceDouble             et;
                SpiceDouble             lt;

                /.
                `state_rec' is the state of Phoebe with respect to CASSINI
                in rectangular coordinates. `state_lat' is the state
                transformed in latitudinal coordinates. `state_rec2' is the
                state transformed back into rectangular coordinates from
                latitudinal.
                ./
                SpiceDouble             state_rec  [6];
                SpiceDouble             state_lat  [6];
                SpiceDouble             state_rec2 [6];

                /.
                The required kernels must be loaded.
                ./
                furnsh_c ( METAKR );

                /.
                Calculate the state at 2004 Jun 11 19:32:00 UTC.
                ./
                str2et_c ( "2004-JUN-11-19:32:00", &et );

                /.
                Calculate the apparent state of Phoebe as seen by
                Cassini in the J2000 frame.
                ./
                spkezr_c ( "phoebe",  et, "iau_phoebe", "lt+s",
                           "cassini", state_rec, &lt );

                /.
                Transform the state from rectangular to latitudinal.
                Notice that since neither the input nor output
                coordinate frames are 'geodetic' or 'planetographic',
                the input for the body name is a blank string.
                ./
                xfmsta_c ( state_rec, "rectangular", "latitudinal",
                           " ", state_lat );

                /.
                Transform the state back to rectangular from latitudinal.
                The result should be very close to `state_rec'.
                ./
                xfmsta_c ( state_lat, "latitudinal", "rectangular",
                           " ", state_rec2 );

                /.
                Report the results.
                ./
                printf ( "\n"
                         "Phoebe as seen by Cassini - rectangular\n"
                         "  Position [km]:\n"
                         "    %16.6f %16.6f %16.6f\n"
                         "  Velocity [km/s]:\n"
                         "    %16.6f %16.6f %16.6f\n\n"
                         "Phoebe as seen by Cassini - latitudinal\n"
                         "  Position [km, rad, rad]:\n"
                         "    %16.6f %16.6f %16.6f\n"
                         "  Velocity [km/s, rad/s, rad/s]:\n"
                         "    %16.6f %16.6f %16.6f\n\n"
                         "Verification:\n"
                         "Phoebe as seen by Cassini - rectangular\n"
                         "  Position [km]:\n"
                         "    %16.6f %16.6f %16.6f\n"
                         "  Velocity [km/s]:\n"
                         "    %16.6f %16.6f %16.6f\n",
                         state_rec [0], state_rec [1], state_rec [2],
                         state_rec [3], state_rec [4], state_rec [5],
                         state_lat [0], state_lat [1], state_lat [2],
                         state_lat [3], state_lat [4], state_lat [5],
                         state_rec2[0], state_rec2[1], state_rec2[2],
                         state_rec2[3], state_rec2[4], state_rec2[5] );

                return(0);

             }

          When this program was executed on a PC/Linux/gcc platform, the
          output was:

             Phoebe as seen by Cassini - rectangular
               Position [km]:
                     -1982.639762      -934.530471      -166.562595
               Velocity [km/s]:
                         3.970832        -3.812496        -2.371663

             Phoebe as seen by Cassini - latitudinal
               Position [km, rad, rad]:
                      2198.169858        -2.701121        -0.075846
               Velocity [km/s, rad/s, rad/s]:
                        -1.780939         0.002346        -0.001144

             Verification:
             Phoebe as seen by Cassini - rectangular
               Position [km]:
                     -1982.639762      -934.530471      -166.562595
               Velocity [km/s]:
                         3.970832        -3.812496        -2.371663

       2) Transform a given state from cylindrical to planetographic
          coordinates with respect to Earth.

             #include <stdio.h>
             #include "SpiceUsr.h"

             int main()
             {

                /.
                Local variables

                `state_cyl' is the state in cylindrical coordinates.
                `state_pln' is the state transformed into planetographic
                coordinates. `state_cyl2' is the state transformed
                back into cylindrical coordinates from planetographic.
                ./
                SpiceDouble     state_cyl  [6] = {1, 0.5, 0.5, 0.2, 0.1, -0.2};
                SpiceDouble     state_pln  [6];
                SpiceDouble     state_cyl2 [6];

                /.
                The required kernels must be loaded.
                ./
                furnsh_c ( "cpck05Mar2004.tpc" );

                /.
                Transform the state from cylindrical to planetographic.
                Note that since one of the coordinate systems is
                planetographic, the body name must be input.
                ./
                xfmsta_c ( state_cyl, "cylindrical", "planetographic",
                           "earth", state_pln );

                /.
                Transform the state back to cylindrical from planetographic.
                The result should be very close to `state_cyl'.
                ./
                xfmsta_c ( state_pln, "planetographic", "cylindrical",
                           "earth", state_cyl2 );

                /.
                Report the results.
                ./
                printf ( "\n"
                         "Cylindrical state\n"
                         "  Position [km, rad, km]:\n"
                         "    %16.6f %16.6f %16.6f\n"
                         "  Velocity [km/s, rad/s, km/s]:\n"
                         "    %16.6f %16.6f %16.6f\n\n"
                         "Planetographic state\n"
                         "  Position  [rad, rad, km]:\n"
                         "    %16.6f %16.6f %16.6f\n"
                         "  Velocity [rad/s, rad/s, km/s]:\n"
                         "    %16.6f %16.6f %16.6f\n\n"
                         "Verification:  Cylindrical state\n"
                         "  Position [km, rad, km]:\n"
                         "    %16.6f %16.6f %16.6f\n"
                         "  Velocity [km/s, rad/s, km/s]:\n"
                         "    %16.6f %16.6f %16.6f\n",
                         state_cyl [0], state_cyl [1], state_cyl [2],
                         state_cyl [3], state_cyl [4], state_cyl [5],
                         state_pln [0], state_pln [1], state_pln [2],
                         state_pln [3], state_pln [4], state_pln [5],
                         state_cyl2[0], state_cyl2[1], state_cyl2[2],
                         state_cyl2[3], state_cyl2[4], state_cyl2[5] );

                return(0);

             }

          When this program was executed on a PC/Linux/gcc platform, the
          output was:

             Cylindrical state
               Position [km, rad, km]:
                         1.000000         0.500000         0.500000
               Velocity [km/s, rad/s, km/s]:
                         0.200000         0.100000        -0.200000

             Planetographic state
               Position  [rad, rad, km]:
                         0.500000         1.547727     -6356.238467
               Velocity [rad/s, rad/s, km/s]:
                         0.100000        -0.004721        -0.195333

             Verification:  Cylindrical state
               Position [km, rad, km]:
                         1.000000         0.500000         0.500000
               Velocity [km/s, rad/s, km/s]:
                         0.200000         0.100000        -0.200000

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

       S.C. Krening   (JPL)
       B.V. Semenov   (JPL)

#### Version

       -CSPICE Version 1.1.0, 09-FEB-2017 (BVS)

          BUG FIX: the routine no longer allows converting to and from
          geodetic and planetographic coordinates for bodies with
          unequal equatorial radii. Previously it arbitrarily picked the
          first and the third radii to compute body's flattening
          coefficient.

       -CSPICE Version 1.0.0, 30-JAN-2011 (SCK)

#### Index_Entries

       state transformation between coordinate systems
       convert state

#### Link to routine xfmsta_c source file xfmsta_c.c

    Wed Apr  5 17:54:48 2017