| xfmsta_c |
|
Table of contents
Procedure
xfmsta_c ( Transform state between coordinate systems )
void xfmsta_c ( ConstSpiceDouble istate[6],
ConstSpiceChar * icosys,
ConstSpiceChar * ocosys,
ConstSpiceChar * body,
SpiceDouble ostate[6] )
AbstractTransform a state between coordinate systems. Required_ReadingNone. KeywordsCONVERSION COORDINATE EPHEMERIS STATE Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
istate I Input state.
icosys I Current (input) coordinate system.
ocosys I Desired (output) coordinate system.
body I Name or NAIF ID of body with which
coordinates are associated (if applicable).
ostate O Converted output state.
Detailed_Input
istate is a state vector in the input `icosys' 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.
icosys is the name of the coordinate system that the input
state vector `istate' is currently in.
`icosys' 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.
ocosys is the name of the coordinate system that the state
should be converted to.
Please see the description of `icosys' 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' is ignored. It may
be a blank string.
Examples of accepted body names or IDs are:
"Earth"
"399"
Leading spaces, trailing spaces, and letter case are
ignored.
Detailed_Output
ostate is the state vector that has been converted to the
output coordinate system `ocosys'.
ParametersNone. Exceptions
1) If either the input or output coordinate system is not
recognized, the error SPICE(COORDSYSNOTREC) is signaled by a
routine in the call tree of this routine.
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 by a routine in
the call tree of this routine.
3) If the input state `istate' is not valid, meaning the position
but not the velocity is along the Z-axis, the error
SPICE(INVALIDSTATE) is signaled by a routine in the call tree
of this routine.
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) is
signaled by a routine in the call tree of this routine.
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) is signaled by a
routine in the call tree of this routine.
6) If the product of the Jacobian and velocity components may
lead to numeric overflow, the error SPICE(NUMERICOVERFLOW) is
signaled by a routine in the call tree of this routine.
7) 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.
8) If the size of the `body' radii kernel variable is not three,
an error is signaled by a routine in the call tree of this
routine.
9) If any of the three `body' radii is less-than or equal to zero,
an error is signaled by a routine in the call tree of this
routine.
10) 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 by a routine in the call
tree of this routine.
11) If any of the `icosys', `ocosys' or `body' input string
pointers is null, the error SPICE(NULLPOINTER) is signaled.
12) If any of the `icosys', `ocosys' or `body' input strings has
zero length, the error SPICE(EMPTYSTRING) is signaled.
FilesSPK, 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 longitudes, `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
--------- --------
pck00010.tpc Planet orientation and
radii
naif0012.tls Leapseconds
041014R_SCPSE_01066_04199.bsp CASSINI, planetary and
Saturn Satellite
ephemeris
\begindata
KERNELS_TO_LOAD = ( 'naif0012.tls',
'041014R_SCPSE_01066_04199.bsp',
'pck00010.tpc' )
\begintext
End of meta-kernel
Example code begins here.
/.
Program xfmsta_ex1
./
#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, < );
/.
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 Mac/Intel/cc/64-bit
platform, the output was:
Phoebe as seen by Cassini - rectangular
Position [km]:
-2059.271283 -942.128329 -95.837672
Velocity [km/s]:
3.910113 -4.228139 -1.526561
Phoebe as seen by Cassini - latitudinal
Position [km, rad, rad]:
2266.580876 -2.712515 -0.042296
Velocity [km/s, rad/s, rad/s]:
-1.730462 0.002416 -0.000706
Verification:
Phoebe as seen by Cassini - rectangular
Position [km]:
-2059.271283 -942.128329 -95.837672
Velocity [km/s]:
3.910113 -4.228139 -1.526561
2) Transform a given state from cylindrical to planetographic
coordinates with respect to Earth.
Use the PCK kernel below to load the required triaxial
ellipsoidal shape model and orientation data for the Earth.
pck00010.tpc
Example code begins here.
/.
Program xfmsta_ex2
./
#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 ( "pck00010.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 Mac/Intel/cc/64-bit
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 1.547722 -6356.240364
Velocity [rad/s, rad/s, km/s]:
0.100000 -0.004722 -0.195332
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
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionJ. Diaz del Rio (ODC Space) S.C. Krening (JPL) B.V. Semenov (JPL) Version
-CSPICE Version 1.2.0, 01-NOV-2021 (JDR)
Updated -Exceptions section with description of missing
exceptions and its format to comply with NAIF standard.
Changed argument names "input_state", "input_coord_sys",
"output_coord_sys" and "output_state" to "istate", "icosys",
"ocosys" and "ostate" for consistency with other functions.
Edits to the header to comply with NAIF standard.
Added missing begintext tag in example's meta-kernel.
Updated Examples' kernels set to use PDS archived data.
-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_Entriesstate transformation between coordinate systems convert state |
Fri Dec 31 18:41:15 2021