Mapping Toolbox

departure

Compute departure between longitudes at specified latitudes

Syntax

• dist = departure(long1,long2,lat)
  dist = departure(long1,long2,lat,units)
  dist = departure(long1,long2,lat,geoid)
  dist = departure(long1,long2,lat,geoid,units)
  

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.

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 direction 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,geoid) specifies the elliptical definition of the Earth to be used with the two-element geoid vector. The default geoid model is a unit sphere, which is sufficient for most applications. When a geoid model is input, the resulting distance is given in terms of the distance units in the geoid vector, regardless of the angle units used.

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 a geoid is used, the result is more complicated. The distance at 60° is not exactly twice the 0° value:

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

See Also

distance	Distance between two points
stdm	Standard deviation for geographic data

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