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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.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 |