beamToXyzAdp {oce} | R Documentation |
Convert ADP velocity components from a beam-based coordinate system to a xyz-based coordinate system.
beamToXyzAdp(x, debug=getOption("oceDebug"))
x |
an object of class |
debug |
a debugging flag, 0 for no debugging, and higher values for more and more debugging. |
The action depends on the type of object.
For a 3-beam aquadopp
object, the beams are transformed
into velocities using the matrix stored in the header.
For 4-beam rdi
object, the beams are converted to velocity
components using formulae from section 5.5 of RD Instruments
(1998), viz. the along-beam velocity components
B1,
B2,
B3,
and
B4
are used to calculate velocity components in a cartesian
system referenced to the instrument using the following formulae:
u=c*a*(B1-B2),
v=c*a*(B4-B3),
w=-b*(B1+B2+B3+B4),
and an estimate of the error in velocity is calculated using
e=d*(B1 + B2 - B3 - B4)
(Note that the multiplier on e is subject to discussion; RDI suggests one multiplier, but some oceanographers favour another.)
In the above, c=1 if the beam geometry is convex, and c=-1 if the beam geometry is concave, a=1/(2*sin(theta)), b=1/(4*cos(theta)) and d=a/sqrt(2), where theta is the angle the beams make to the instrument “vertical”.
An object with the first 3 velocitiy indices having been
altered to represent velocity components in xyz (or instrument)
coordinates. (For rdi
data, the values at the 4th velocity
index are changed to represent the "error" velocity.)
To indicate the change, the value of metadata$oce.orientation
is changed from beam
to xyz
.
Dan Kelley
1. R D Instruments, 1998. ADP Coordinate Transformation, formulas and calculations. P/N 951-6079-00 (July 1998).
2. WHOI/USGS-provided Matlab code for beam-enu transformation http://woodshole.er.usgs.gov/pubs/of2005-1429/MFILES/AQDPTOOLS/beam2enu.m
See read.adp
for other functions that relate to objects
of class "adp"
.