cspice_el2cgv

 Abstract I/O Examples Particulars Required Reading Version Index_Entries
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```

#### Abstract

```
CSPICE_EL2CGV converts an Icy ellipse to a center vector and
two generating vectors. The selected generating vectors are
semi-axes of the ellipse.

For important details concerning this module's function, please refer to
the CSPICE routine el2cgv_c.

```

#### I/O

```
Given:

ellipse   a structure describing a SPICE ellipse. The structure has
the fields:

center:    dblarr(3)
semimajor: dblarr(3)
semiminor: dblarr(3)

the call:

cspice_el2cgv, ellipse, center, smajor, sminor

returns:

center    the double precision 3-vector defining the center
of 'ellipse'

smajor    the double precision 3-vector defining the semi-major
axis of 'ellipse'

sminor    the double precision 3-vector defining the semi-minor
axis of 'ellipse'. This ellipse is the set of points

center + cos(theta) smajor + sin(theta) sminor

where theta ranges over the interval (-pi, pi].

```

#### Examples

```
Any 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.

;;
;; Define two arbitrary, linearly independent vectors
;; and a center vector.
;;
vec1    = [ 1.d,  1.d, 1.d ]
vec2    = [ 1.d, -1.d, 1.d ]
center  = [ 1.d,  1.d, 1.d ]

;;
;; Calculate the semi-major and semi-minor axes of
;; the ellipse as generated by 'vec1' and 'vec2'.
;; (The cspice_saelgv call determines the orthogonal axes
;; of an ellipse from two generating vectors.)
;;
cspice_saelgv, vec1, vec2, smajor, sminor

;;
;; Load the generating vectors into an ellipse structure.
;;
cspice_cgv2el, center, smajor, sminor, ellipse

;;
;; Extract the CSPICE_ELLIPSE structure components into
;; variable.
;;
cspice_el2cgv, ellipse, cent, smaj, smin
print, cent
print, smaj
print, smin

IDL outputs for 'cent':
1.0000000       1.0000000      1.0000000

IDL outputs for 'smaj':
1.4142136       1.2329564e-16  1.4142136

IDL outputs for 'smin':
-6.1647820e-17   1.4142136     -6.1647820e-17

Realize, values on the order of 10E-16 are within double precision
round-off to zero.

The call does nothing but extract the 3-vector components of the
CSPICE_ELLIPSE structure into individual 3-vectors.

IDL native code to perform the same operation:

cent = ellipse.center
smaj = ellipse.semimajor
smin = ellipse.semiminor

```

```
None.

```

```
ICY.REQ
ELLIPSES.REQ

```

#### Version

```
-Icy Version 1.0.2, 07-FEB-2012, EDW (JPL)

Clarified description of 'ellipse' output argument. A 'SPICE ellipse'
not an 'Icy ellipse'.

-Icy Version 1.0.1, 07-MAY-2008, EDW (JPL)

Expanded description of Abstract, input, and output variables.

-Icy Version 1.0.0, 16-JUN-2003, EDW (JPL)

```

#### Index_Entries

```
ellipse to center and generating vectors

```
`Wed Apr  5 17:58:01 2017`