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.
# S4 method for oce
applyMagneticDeclination(
object = "oce",
declination = 0,
debug = getOption("oceDebug")
)an object of the same class as object, modified as outlined in
“Details”.
an object of cm, adp, or adv class.
numeric value holding magnetic declination in degrees, positive for clockwise from north.
a debugging flag, set to a positive value to get debugging.
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(),
applyMagneticDeclination,adp-method,
applyMagneticDeclination,adv-method,
applyMagneticDeclination,cm-method,
magneticField()