xyzToEnuAdv: Convert an adv Object From XYZ to ENU Coordinates

Description

Convert ADV velocity components from a xyz-based coordinate system to an enu-based coordinate system.

Usage

xyzToEnuAdv(
  x,
  declination = 0,
  cabled = FALSE,
  horizontalCase,
  sensorOrientation,
  debug = getOption("oceDebug")
)

Arguments

x: an adv object.
declination: magnetic declination to be added to the heading after "righting" (see below), to get ENU with N as "true" north. If this is set to NULL, then the returned object is set up without adjusting the compass for declination. That means that north in its metadata slot will be set to "magnetic", and also that there will be no item named declination in that slot. Note that applyMagneticDeclination() can be used later, to set a declination.
cabled: boolean value indicating whether the sensor head is connected to the pressure case with a cable. If cabled=FALSE, then horizontalCase is ignored. See “Details”.
horizontalCase: optional boolean value indicating whether the sensor case is oriented horizontally. Ignored unless cabled is TRUE. See “Details”.
sensorOrientation: optional string indicating the direction in which the sensor points. The value, which must be "upward" or "downward", over-rides the value of orientation, in the metadata slot, which will have been set by read.adv(), provided that the data file contained the full header. See “Details”.
debug: a flag that, if non-zero, turns on debugging. Higher values yield more extensive debugging.

Author

Dan Kelley, in collaboration with Clark Richards

Details

The coordinate transformation is done using the heading, pitch, and roll information contained within x. The algorithm is similar to that used for Teledyne/RDI ADCP units, taking into account the different definitions of heading, pitch, and roll as they are defined for the velocimeters.

Generally, the transformation must be done on a time-by-time basis, which is a slow operation. However, this function checks whether the vectors for heading, pitch and roll, are all of unit length, and in that case, the calculation is altered, resulting in shorter execution times. Note that the angles are held in (data$timeSlow, data$headingSlow, ...) for Nortek instruments and (data$time, data$heading, ...) for Sontek instruments.

Since the documentation provided by instrument manufacturers can be vague on the coordinate transformations, the method used here had to be developed indirectly. (This is in contrast to the RDI ADCP instruments, for which there are clear instructions.) documents that manufacturers provide. If results seem incorrect (e.g. if currents go east instead of west), users should examine the code in detail for the case at hand. The first step is to set debug to 1, so that the processing will print a trail of processing steps. The next step should be to consult the table below, to see if it matches the understanding (or empirical tests) of the user. It should not be difficult to tailor the code, if needed.

The code handles every case individually, based on the table given below. The table comes from Clark Richards, a former PhD student at Dalhousie University (reference 2), who developed it based on instrument documentation, discussion on user groups, and analysis of measurements acquired with Nortek and Sontek velocimeters in the SLEIWEX experiment.

The column labelled Cabled'' indicates whether the sensor and the pressure case are connected with a flexible cable, and the column labelled H.case'' indicates whether the pressure case is oriented horizontally. These two properties are not discoverable in the headers of the data files, and so they must be supplied with the arguments cabled and horizontalCase. The source code refers to the information in this table by case numbers. (Cases 5 and 6 are not handled.) Angles are abbreviated as follows:: heading H,'' pitch P,'' and roll ``R''. Entries X, Y and Z refer to instrument coordinates of the same names. Entries S, F and M refer to so-called ship coordinates starboard, forward, and mast; it is these that are used together with a rotation matrix to get velocity components in the east, north, and upward directions.

`Case`	`Mfr.`	`Instr.`	`Cabled`	`H. case`	`Orient.`	`H`	`P`	`R`	`S`	`F`	`M`
1	Nortek	vector	no	-	up	H-90	R	-P	X	-Y	-Z
2	Nortek	vector	no	-	down	H-90	R	-P	X	Y	Z
3	Nortek	vector	yes	yes	up	H-90	R	-P	X	Y	Z
4	Nortek	vector	yes	yes	down	H-90	R	P	X	-Y	-Z
5	Nortek	vector	yes	no	up	-	-	-	-	-	-
6	Nortek	vector	yes	no	down	-	-	-	-	-	-
7	Sontek	adv	-	-	up	H-90	R	-P	X	-Y	-Z
8	Sontek	adv	-	-	down	H-90	R	-P	X	Y	Z

References