Gravity: Gravity
In WilliamCooper/Ranadu: Functions for use with RAF aircraft data files

Provides the acceleration caused by gravity.

1	Gravity(latitude, altitude = 0)

`latitude`	The latitude (or vector of latitudes) in units of degrees N.
`altitude`	The altitude in meters above the WGS-84 geoid. GPS measurements before correction to MSL are appropriate to use when supplying this altitude. For detailed accuracy, correct a variable like GGALT by adding the height of the geoid above the WGS84 reference ellipsoid. In RAF datasets, this may be present as the variable GGEOIDHT.

The formula used incorporates the dependence on latitude and on altitude above the WGS-84 geoid.

The acceleration of gravity in units of m/s^2

William Cooper