# scircle1

Small circles from center, range, and azimuth

## Syntax

`[lat,lon] = scircle1(lat0,lon0,rad)`

[lat,lon] = scircle1(lat0,lon0,rad,az)

[lat,lon] = scircle1(lat0,lon0,rad,az,ellipsoid)

[lat,lon] = scircle1(lat0,lon0,rad,units)

[lat,lon] = scircle1(lat0,lon0,rad,az,units)

[lat,lon] = scircle1(lat0,lon0,rad,az,ellipsoid,units)

[lat,lon] = scircle1(lat0,lon0,rad,az,ellipsoid,* units*,npts)

[lat,lon] = scircle1(track,...)

## Description

`[lat,lon] = scircle1(lat0,lon0,rad)`

computes
small circles (on a sphere) with a center at the point `lat0,lon0`

and
radius `rad`

. The inputs can be scalar or column
vectors. The input radius is in degrees of arc length on a sphere.

`[lat,lon] = scircle1(lat0,lon0,rad,az)`

uses
the input `az`

to define the small circle arcs computed.
The arc azimuths are measured clockwise from due north. If `az`

is
a column vector, then the arc length is computed from due north. If `az`

is
a two-column matrix, then the small circle arcs are computed starting
at the azimuth in the first column and ending at the azimuth in the
second column. If `az = []`

, then a complete small
circle is computed.

`[lat,lon] = scircle1(lat0,lon0,rad,az,ellipsoid)`

computes small circles
on the ellipsoid defined by the input `ellipsoid`

, rather than by
assuming a sphere. `ellipsoid`

is a `referenceSphere`

, `referenceEllipsoid`

, or `oblateSpheroid`

object, or a vector of the form ```
[semimajor_axis
eccentricity]
```

. If the semimajor axis is non-zero, `rad`

is assumed to be in distance units matching the units of the semimajor axis. However, if
`ellipsoid = []`

, or if the semimajor axis is zero, then
`rad`

is interpreted as an angle and the small circles are computed
on a sphere as in the preceding syntax.

`[lat,lon] = scircle1(lat0,lon0,rad,units)`

,

`[lat,lon] = scircle1(lat0,lon0,rad,az,units)`

, and

`[lat,lon] = scircle1(lat0,lon0,rad,az,ellipsoid,units)`

are
all valid calling forms, which use the input units to define the angle units of the
inputs and outputs. If you omit units, `'degrees'`

is assumed.

`[lat,lon] = scircle1(lat0,lon0,rad,az,ellipsoid,`

uses
the scalar input * units*,npts)

`npts`

to determine the number of
points per small circle computed. The default value of `npts`

is
100.`[lat,lon] = scircle1(track,...)`

uses track to define either a great
circle or rhumb line radius. If

, then small circles are computed. If * track* =
'gc'

`track = 'rh'`

,
then the circles with radii of constant rhumb line distance are computed. If you omit
track, `'gc'`

is assumed.`mat = scircle1(...)`

returns a single output
argument where `mat = [lat lon]`

. This is useful
if a single small circle is computed.

Multiple circles can be defined from a single starting point
by providing scalar `lat0,lon0`

inputs and column
vectors for `rad`

and `az`

if desired.

## Examples

Create and plot a small circle centered at (0º,0º) with a radius of 10º.

axesm('mercator','MapLatLimit',[-30 30],'MapLonLimit',[-30 30]); [latc,longc] = scircle1(0,0,10); plotm(latc,longc,'g')

If the desired radius is known in some nonangular distance unit,
use the radius returned by the `earthRadius`

function
as the ellipsoid input to set the range units. (Use an empty azimuth
entry to indicate a full circle.)

[latc,longc] = scircle1(0,0,550,[],earthRadius('nm')); plotm(latc,longc,'r')

For just an arc of the circle, enter an azimuth range.

[latc,longc] = scircle1(0,0,5,[-30 70]); plotm(latc,longc,'m')

## More About

## Version History

**Introduced before R2006a**