## Syntax

`dist = departure(long1,long2,lat)`

dist = departure(long1,long2,lat,ellipsoid)

dist = departure(long1,long2,lat,`units`

)

dist = departure(long1,long2,lat,geoid,`units`

)

## Description

`dist = departure(long1,long2,lat)`

computes
the departure distance from `long1`

to `long2`

at
the input latitude `lat`

. Departure is the distance
along a specific parallel between two meridians. The output `dist`

is
returned in degrees of arc length on a sphere.

`dist = departure(long1,long2,lat,ellipsoid)`

computes
the departure assuming that the input points lie on the ellipsoid
defined by the input `ellipsoid`

. `ellipsoid`

is
a `referenceSphere`

, `referenceEllipsoid`

, or `oblateSpheroid`

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

.

`dist = departure(long1,long2,lat,``units`

)

uses
the input string `units`

to define the angle
units of the input and output data. In this form, the departure is
returned as an arc length in the units specified by `units`

.
If `units`

is omitted, `'degrees'`

is
assumed.

`dist = departure(long1,long2,lat,geoid,``units`

)

is
a valid calling form. In this case, the departure is computed in the
same units as the semimajor axes of the ellipsoid.

## Definitions

*Departure* is the distance along a parallel
between two points. Whereas a degree of latitude is always the same
distance, a degree of longitude is different in length at different
latitudes. In practice, this distance is usually given in nautical
miles.

## Examples

On a spherical Earth, the departure is proportional to the cosine
of the latitude:

distance = departure(0, 10, 0)
distance =
10
distance = departure(0, 10, 60)
distance =
5

When an ellipsoid is used, the result is more complicated. The
distance at 60º is not exactly twice the 0º value:

distance = departure(0, 10, 0, referenceEllipsoid('earth', 'nm'))
distance =
601.0772
distance = departure(0, 10, 60, referenceEllipsoid('earth', 'nm'))
distance =
299.7819