drdpgr_c

 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 drdpgr_c ( ConstSpiceChar  * body,
SpiceDouble       lon,
SpiceDouble       lat,
SpiceDouble       alt,
SpiceDouble       re,
SpiceDouble       f,
SpiceDouble       jacobi )

```

#### Abstract

```
This routine computes the Jacobian matrix of the transformation
from planetographic to rectangular coordinates.
```

```
None.
```

```
COORDINATES
DERIVATIVES
MATRIX

```

#### Brief_I/O

```
Variable  I/O  Description
--------  ---  --------------------------------------------------
body       I   Name of body with which coordinates are associated.
lon        I   Planetographic longitude of a point (radians).
lat        I   Planetographic latitude of a point (radians).
alt        I   Altitude of a point above reference spheroid.
re         I   Equatorial radius of the reference spheroid.
f          I   Flattening coefficient.
jacobi     O   Matrix of partial derivatives.
```

#### Detailed_Input

```
body       Name of the body with which the planetographic
coordinate system is associated.

`body' is used by this routine to look up from the
kernel pool the prime meridian rate coefficient giving
the body's spin sense.  See the Files and Particulars

lon        Planetographic longitude of the input point.  This is
the angle between the prime meridian and the meridian
containing the input point.  For bodies having
prograde (aka direct) rotation, the direction of
increasing longitude is positive west:  from the +X
axis of the rectangular coordinate system toward the
-Y axis.  For bodies having retrograde rotation, the
direction of increasing longitude is positive east:
from the +X axis toward the +Y axis.

The earth, moon, and sun are exceptions:
planetographic longitude is measured positive east for
these bodies.

The default interpretation of longitude by this
and the other planetographic coordinate conversion
routines can be overridden; see the discussion in
Particulars below for details.

Longitude is measured in radians. On input, the range
of longitude is unrestricted.

lat        Planetographic latitude of the input point.  For a
point P on the reference spheroid, this is the angle
between the XY plane and the outward normal vector at
P. For a point P not on the reference spheroid, the
planetographic latitude is that of the closest point
to P on the spheroid.

Latitude is measured in radians.  On input, the
range of latitude is unrestricted.

alt        Altitude of point above the reference spheroid.
Units of `alt' must match those of `re'.

re         Equatorial radius of a reference spheroid.  This
spheroid is a volume of revolution:  its horizontal
cross sections are circular.  The shape of the
spheroid is defined by an equatorial radius `re' and
a polar radius `rp'.  Units of `re' must match those of
`alt'.

f          Flattening coefficient =

(re-rp) / re

where `rp' is the polar radius of the spheroid, and the
units of `rp' match those of `re'.
```

#### Detailed_Output

```
JACOBI     is the matrix of partial derivatives of the conversion
from planetographic to rectangular coordinates.  It
has the form

.-                              -.
|  DX/DLON   DX/DLAT   DX/DALT   |
|  DY/DLON   DY/DLAT   DY/DALT   |
|  DZ/DLON   DZ/DLAT   DZ/DALT   |
`-                              -'

evaluated at the input values of `lon', `lat' and `alt'.
```

```
None.
```

#### Exceptions

```
1) If the body name `body' cannot be mapped to a NAIF ID code,
and if `body' is not a string representation of an integer,
the error SPICE(IDCODENOTFOUND) will be signaled.

2) If the kernel variable

BODY<ID code>_PGR_POSITIVE_LON

is present in the kernel pool but has a value other
than one of

'EAST'
'WEST'

the error SPICE(INVALIDOPTION) will be signaled.  Case
and blanks are ignored when these values are interpreted.

3) If polynomial coefficients for the prime meridian of `body'
are not available in the kernel pool, and if the kernel
variable BODY<ID code>_PGR_POSITIVE_LON is not present in
the kernel pool, the error SPICE(MISSINGDATA) will be signaled.

4) If the equatorial radius is non-positive, the error
SPICE(VALUEOUTOFRANGE) is signaled.

5) If the flattening coefficient is greater than or equal to one,
the error SPICE(VALUEOUTOFRANGE) is signaled.

6) The error SPICE(EMPTYSTRING) is signaled if the input
string `body' does not contain at least one character, since the
input string cannot be converted to a Fortran-style string in
this case.

7) The error SPICE(NULLPOINTER) is signaled if the input string
pointer `body' is null.
```

#### Files

```
This routine expects a kernel variable giving body's prime
meridian angle as a function of time to be available in the
file.  The required kernel variable is named

BODY<body ID>_PM

where <body ID> represents a string containing the NAIF integer
ID code for `body'.  For example, if `body' is "JUPITER", then
the name of the kernel variable containing the prime meridian
angle coefficients is

BODY599_PM

See the PCK Required Reading for details concerning the prime
meridian kernel variable.

The optional kernel variable

BODY<body ID>_PGR_POSITIVE_LON

variable is present in the kernel pool, the prime meridian
coefficients for `body' are not required by this routine. See the
Particulars section below for details.
```

#### Particulars

```
It is often convenient to describe the motion of an object in the
planetographic coordinate system.  However, when performing
vector computations it's hard to beat rectangular coordinates.

To transform states given with respect to planetographic
coordinates to states with respect to rectangular coordinates,
one makes use of the Jacobian of the transformation between the
two systems.

Given a state in planetographic coordinates

( lon, lat, alt, dlon, dlat, dalt )

the velocity in rectangular coordinates is given by the matrix
equation:

t          |                                  t
(dx, dy, dz)   = jacobi|              * (dlon, dlat, dalt)
|(lon,lat,alt)

This routine computes the matrix

|
jacobi|
|(lon,lat,alt)

In the planetographic coordinate system, longitude is defined
using the spin sense of the body.  Longitude is positive to the
west if the spin is prograde and positive to the east if the spin
is retrograde.  The spin sense is given by the sign of the first
degree term of the time-dependent polynomial for the body's prime
meridian Euler angle "W":  the spin is retrograde if this term is
negative and prograde otherwise.  For the sun, planets, most
natural satellites, and selected asteroids, the polynomial
expression for W may be found in a SPICE PCK kernel.

The earth, moon, and sun are exceptions: planetographic longitude
is measured positive east for these bodies.

If you wish to override the default sense of positive longitude
for a particular body, you can do so by defining the kernel
variable

BODY<body ID>_PGR_POSITIVE_LON

where <body ID> represents the NAIF ID code of the body. This
variable may be assigned either of the values

'WEST'
'EAST'

For example, you can have this routine treat the longitude
of the earth as increasing to the west using the kernel
variable assignment

BODY399_PGR_POSITIVE_LON = 'WEST'

Normally such assignments are made by placing them in a text

The definition of this kernel variable controls the behavior of
the CSPICE planetographic routines

pgrrec_c
recpgr_c
dpgrdr_c
drdpgr_c

It does not affect the other CSPICE coordinate conversion
routines.
```

#### Examples

```
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.

Find the planetographic state of the earth as seen from
Mars in the J2000 reference frame at January 1, 2005 TDB.
Map this state back to rectangular coordinates as a check.

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

int main()
{
/.
Local variables
./
SpiceDouble             alt;
SpiceDouble             drectn ;
SpiceDouble             et;
SpiceDouble             f;
SpiceDouble             jacobi ;
SpiceDouble             lat;
SpiceDouble             lon;
SpiceDouble             lt;
SpiceDouble             pgrvel ;
SpiceDouble             re;
SpiceDouble             rectan ;
SpiceDouble             rp;
SpiceDouble             state  ;

SpiceInt                n;

/.
Load a PCK file containing a triaxial
ellipsoidal shape model and orientation
data for Mars.
./
furnsh_c ( "pck00008.tpc" );

/.
Load an SPK file giving ephemerides of earth and Mars.
./
furnsh_c ( "de405.bsp" );

/.
Load a leapseconds kernel to support time conversion.
./
furnsh_c ( "naif0007.tls" );

/.
Look up the radii for Mars.  Although we
omit it here, we could first call badkpv_c
to make sure the variable BODY499_RADII
has three elements and numeric data type.
If the variable is not present in the kernel
pool, bodvrd_c will signal an error.
./

/.
Compute flattening coefficient.
./
f   =  ( re - rp ) / re;

/.
Look up the geometric state of earth as seen from Mars at
January 1, 2005 TDB, relative to the J2000 reference
frame.
./
str2et_c ( "January 1, 2005 TDB", &et);

spkezr_c ( "Earth", et,    "J2000", "LT+S",
"Mars",  state, &lt              );

/.
Convert position to planetographic coordinates.
./
recpgr_c ( "mars", state, re, f, &lon, &lat, &alt );

/.
Convert velocity to planetographic coordinates.
./

dpgrdr_c ( "MARS",  state,  state,  state,
re,      f,         jacobi               );

mxv_c ( jacobi, state+3, pgrvel );

/.
As a check, convert the planetographic state back to
rectangular coordinates.
./
pgrrec_c ( "mars", lon, lat, alt, re, f, rectan );
drdpgr_c ( "mars", lon, lat, alt, re, f, jacobi );

mxv_c ( jacobi, pgrvel, drectn );

printf ( "\n"
"Rectangular coordinates:\n"
"\n"
"  X (km)                 = %18.9e\n"
"  Y (km)                 = %18.9e\n"
"  Z (km)                 = %18.9e\n"
"\n"
"Rectangular velocity:\n"
"\n"
"  dX/dt (km/s)           = %18.9e\n"
"  dY/dt (km/s)           = %18.9e\n"
"  dZ/dt (km/s)           = %18.9e\n"
"\n"
"Ellipsoid shape parameters:\n"
"\n"
"  Equatorial radius (km) = %18.9e\n"
"  Polar radius      (km) = %18.9e\n"
"  Flattening coefficient = %18.9e\n"
"\n"
"Planetographic coordinates:\n"
"\n"
"  Longitude (deg)        = %18.9e\n"
"  Latitude  (deg)        = %18.9e\n"
"  Altitude  (km)         = %18.9e\n"
"\n"
"Planetographic velocity:\n"
"\n"
"  d Longitude/dt (deg/s) = %18.9e\n"
"  d Latitude/dt  (deg/s) = %18.9e\n"
"  d Altitude/dt  (km/s)  = %18.9e\n"
"\n"
"Rectangular coordinates from inverse mapping:\n"
"\n"
"  X (km)                 = %18.9e\n"
"  Y (km)                 = %18.9e\n"
"  Z (km)                 = %18.9e\n"
"\n"
"Rectangular velocity from inverse mapping:\n"
"\n"
"  dX/dt (km/s)           = %18.9e\n"
"  dY/dt (km/s)           = %18.9e\n"
"  dZ/dt (km/s)           = %18.9e\n"
"\n",
state ,
state ,
state ,
state ,
state ,
state ,
re,
rp,
f,
lon / rpd_c(),
lat / rpd_c(),
alt,
pgrvel/rpd_c(),
pgrvel/rpd_c(),
pgrvel,
rectan ,
rectan ,
rectan ,
drectn ,
drectn ,
drectn                 );

return ( 0 );
}

Output from this program should be similar to the following
(rounding and formatting differ across platforms):

Rectangular coordinates:

X (km)                 =    1.460397325e+08
Y (km)                 =    2.785466068e+08
Z (km)                 =    1.197503153e+08

Rectangular velocity:

dX/dt (km/s)           =   -4.704288238e+01
dY/dt (km/s)           =    9.070217780e+00
dZ/dt (km/s)           =    4.756562739e+00

Ellipsoid shape parameters:

Flattening coefficient =    5.886007556e-03

Planetographic coordinates:

Longitude (deg)        =    2.976676591e+02
Latitude  (deg)        =    2.084450403e+01
Altitude  (km)         =    3.365318254e+08

Planetographic velocity:

d Longitude/dt (deg/s) =   -8.357386316e-06
d Latitude/dt  (deg/s) =    1.593493548e-06
d Altitude/dt  (km/s)  =   -1.121443268e+01

Rectangular coordinates from inverse mapping:

X (km)                 =    1.460397325e+08
Y (km)                 =    2.785466068e+08
Z (km)                 =    1.197503153e+08

Rectangular velocity from inverse mapping:

dX/dt (km/s)           =   -4.704288238e+01
dY/dt (km/s)           =    9.070217780e+00
dZ/dt (km/s)           =    4.756562739e+00

```

```
None.
```

```
None.
```

#### Author_and_Institution

```
N.J. Bachman   (JPL)
W.L. Taber     (JPL)
```

#### Version

```
-CSPICE Version 1.0.0, 26-DEC-2004 (NJB) (WLT)
```

#### Index_Entries

```
Jacobian of rectangular w.r.t. planetographic coordinates
```
`Wed Apr  5 17:54:32 2017`