Mapping Toolbox

departure

Compute departure between longitudes at specified latitudes

Syntax

dist = departure(long1,long2,lat) returns the departure between two longitudes at a given latitude in degrees. Departure is dimensionless; the shorter of the two directions is taken from the first longitude to the second.
The distance is given in degrees of arc length.

dist = departure(long1,long2,lat,units) specifies the valid angle units string to apply to the latitude, longitudes, and output distance.

dist = departure(long1,long2,lat,ellipsoid) specifies the elliptical definition of the Earth to be used with the two-element ellipsoid vector. The default ellipsoid model is a unit sphere, which is sufficient for most applications. When a ellipsoid model is input, the resulting distance is given in terms of the distance units in the ellipsoid vector, regardless of the angle units used.

Description

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

See Also

distance	Distance between two points
stdm	Standard deviation for geographic data

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