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Departure of longitudes at specified latitudes
dist = departure(long1,long2,lat)
dist = departure(long1,long2,lat,ellipsoid)
dist = departure(long1,long2,lat,units)
dist = departure(long1,long2,lat,geoid,units)
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.
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.
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