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 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

```   recrad_c ( Rectangular coordinates to RA and DEC )

SpiceDouble       * range,
SpiceDouble       * ra,
SpiceDouble       * dec      )

```

#### Abstract

```   Convert rectangular coordinates to range, right ascension, and
declination.
```

```   None.
```

#### Keywords

```   CONVERSION
COORDINATES

```

#### Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  --------------------------------------------------
rectan     I   Rectangular coordinates of a point.
range      O   Distance of the point from the origin.
ra         O   Right ascension in radians.
```

#### Detailed_Input

```   rectan      are the rectangular coordinates of a point.
```

#### Detailed_Output

```   range       is the distance of the point `rectan' from the origin.

The units associated with `range' are those associated
with the input `rectan'.

ra          is the right ascension of `rectan'. This is the angular
distance measured toward the east from the prime meridian
to the meridian containing the input point. The direction
of increasing right ascension is from the +X axis towards
the +Y axis.

`ra' is output in radians. The range of `ra' is [0, 2*pi].

dec         is the declination of `rectan'. This is the angle from
the XY plane of the ray from the origin through the
point.

`dec' is output in radians. The range of `dec' is
[-pi/2, pi/2].
```

#### Parameters

```   None.
```

#### Exceptions

```   Error free.

1)  If the X and Y components of `rectan' are both zero, the
right ascension is set to zero.

2)  If `rectan' is the zero vector, right ascension and declination
are both set to zero.
```

#### Files

```   None.
```

#### Particulars

```   None.
```

#### Examples

```   The following code fragment converts right ascension and
declination from the B1950 reference frame to the J2000 frame.

#include "SpiceUsr.h"

SpiceDouble      ra;
SpiceDouble      dec;
SpiceDouble      r;
SpiceDouble      mtrans  [ 3 ][ 3 ];
SpiceDouble      v1950   [ 3 ];
SpiceDouble      v2000   [ 3 ];

/.
Convert RA and DEC to a 3-vector expressed in the B1950 frame.
./
radrec_c ( 1.0, ra, dec, v1950 );

/.
We use the CSPICE routine pxform_c to obtain the transformation
matrix for converting vectors between the B1950 and J2000
reference frames. Since both frames are inertial, the input time
value we supply to pxform_c is arbitrary. We choose zero seconds
past the J2000 epoch as the input value.
./
pxform_c ( "B1950", "J2000", 0.0, mtrans );

/.
Transform the vector to the J2000 frame.
./
mxv_c    ( mtrans, v1950, v2000 );

/.
Find the RA and DEC of the J2000-relative vector.
./
recrad_c ( v2000, &r, &ra, &dec );
```

#### Restrictions

```   None.
```

#### Literature_References

```   None.
```

#### Author_and_Institution

```   N.J. Bachman        (JPL)
J. Diaz del Rio     (ODC Space)
E.D. Wright         (JPL)
```

#### Version

```   -CSPICE Version 1.1.3, 04-JUL-2021 (JDR)

Edited the header to comply with NAIF standard.

-CSPICE Version 1.1.2, 30-JUL-2003 (NJB)

-CSPICE Version 1.1.0, 22-OCT-1998 (NJB)

```   rectangular coordinates to ra and dec
`Fri Dec 31 18:41:11 2021`