cspice_drdgeo

 Abstract I/O Examples Particulars Required Reading Version Index_Entries

#### Abstract

```
CSPICE_DRDGEO computes the Jacobian of the transformation from
geodetic to rectangular coordinates.

For important details concerning this module's function, please refer to
the CSPICE routine drdgeo_c.

```

#### I/O

```
Given:

lon   scalar double precision describing the geodetic longitude of
point (radians).

lat   scalar double precision describing the geodetic latitude of
point (radians).

alt   scalar double precision describing the altitude of point above
the reference spheroid. Units of `alt' must match those of `re'.

re    scalar double precision describing the 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     scalar double precision describing the flattening coefficient

f = (re-rp) / re

where rp is the polar radius of the spheroid. (More importantly
rp = re*(1-f).) The units of `rp' match those of `re'.

the call:

cspice_drdgeo, lon, lat, alt, re, f, jacobi

returns:

jacobi   double precision 3x3 matrix describing the matrix of partial
derivatives of the conversion between geodetic and 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.

The formulae for computing 'x', 'y', and 'z' from
geodetic coordinates are given below.

x = [alt +        re/g(lat,f)]*cos(lon)*cos(lat)

y = [alt +        re/g(lat,f)]*sin(lon)*cos(lat)

2
z = [alt + re*(1-f) /g(lat,f)]*         sin(lat)

where

re is the polar radius of the reference spheroid.

f  is the flattening factor (the polar radius is
obtained by multiplying the equatorial radius by 1-f).

g( lat, f ) is given by

2             2     2
sqrt ( cos (lat) + (1-f) * sin (lat) )

```

```
None.

```

#### Particulars

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

To transform states given with respect to geodetic 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 geodetic 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)

```

```
ICY.REQ

```

#### Version

```
-Icy Version 1.0.0, 28-DEC-2010, EDW (JPL)

```

#### Index_Entries

```
Jacobian of rectangular w.r.t. geodetic coordinates

```
`Wed Apr  5 17:58:00 2017`