Current-measuring instruments that infer flow direction using magnetic
compasses require a correction for magnetic declination, in order to infer
currents with x and y oriented eastward and northward, respectively.
applyMagneticDeclination() is a generic function that handles this task by
altering velocity components (and heading values, if they exist). It works
for objects of the cm, adp and adv and cm
classes by calling applyMagneticDeclination,adp-method(),
applyMagneticDeclination,adv-method(), or
applyMagneticDeclination,cm-method(), respectively.
applyMagneticDeclination(object = "oce", declination = "ANY", debug = "ANY")an object of the same class as object, modified as described
in “Details”.
an object of cm, adp, or adv class.
numeric value holding magnetic declination in degrees, positive for clockwise from north.
an integer specifying whether debugging information is
to be printed during the processing. This is a general parameter that
is used by many oce functions. Generally, setting debug=0
turns off the printing, while higher values suggest that more information
be printed. If one function calls another, it usually reduces the value of
debug first, so that a user can often obtain deeper debugging
by specifying higher debug values.
Dan Kelley, aided, for the adp and adv variants, by Clark Richards and Jaimie Harbin.
The returned value is a copy of object that has been modified in 4 ways.
(1) the horizontal components of velocity are rotated clockwise by
declination degrees. (2) If the object holds heading values, then
declination is added to them. (3) The north item in the metadata slot
is set to "geographic", and a warning is issued if this was also the value
in object. (4) The declination item in the metadata slot is set to
the value supplied to this function.
Use magneticField() to determine the declination,
inclination and intensity at a given spot on the world, at a given time.
Other things related to magnetism:
applyMagneticDeclination,adp-method,
applyMagneticDeclination,adv-method,
applyMagneticDeclination,cm-method,
applyMagneticDeclination,oce-method,
magneticField()