cspice_surfnm

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

```
CSPICE_SURFNM computes the double precision, outward-pointing
normal unit 3-vector at a point defined on the surface of an
ellipsoid.

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

```

#### I/O

```
Given:

a,       the scalar double precision values of the ellipsoid's
c
'a' is length in kilometers of the semi-axis of the ellipsoid
parallel to the x-axis of the body-fixed reference frame

'b' is length in kilometers of the semi-axis of the ellipsoid
parallel to the y-axis of the body-fixed reference frame

'c' is length in kilometers of the semi-axis of the ellipsoid
parallel to the z-axis of the body-fixed reference frame

point   a double precision 3-vector defining a location on
the ellipsoid

the call:

cspice_surfnm, a, b, c, point, normal

returns:

normal   a double precision unit 3-vector normal to the
ellipsoid at 'point' in the direction away from the
ellipsoid

```

#### 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 the radii of an ellipsoid.
;;
a  =  1.d
b  =  2.d
c  =  3.d

;;
;; Select a location.
;;
point = [ 0.d, 0.d, 3.d ]

;;
;; calculate the surface normal to the ellipsoid at 'point'.
;;
cspice_surfnm, a, b, c, point, out_norm
print, out_norm

IDL outputs:

0.0000000    0.0000000    1.0000000

```

```
None.

```

```
ICY.REQ
ELLIPSES.REQ

```

#### Version

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

```

#### Index_Entries

```
surface normal vector on an ellipsoid

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`Wed Apr  5 17:58:04 2017`