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Subsections

• Clipping.
• Quack

autoflag.setselect - Function

	Package	synthesis
	Module	autoflag
	Tool	autoflag

Sets up the Selector flagging method

Synopsis
setselect(spwid, field, fq, chan, corr, ant, baseline, timerng, autocorr, timeslot, dtime, clip, flagrange, quack, unflag)

Description

The select method allows you to directly flag or unflag a subset of your data. Subsets can be specified via any combination of field, spectral window, frequency or channel number, correlations (i.e. polarizations), antennas, baselines, time ranges. The method will flag/unflag a whole subset, or, optionally, only autocorrelations, or only specific time slots within the subset. Select also includes the option to flag VLA quacks (specified by scan interval and scan start time).

The spwid, field, fq, chan, corr, ant, baseline, timerng parameters select a subset of the measurement set, on a logical-AND basis.

• An empty array ([]) or a boolean F (which is the default for any parameter), means ``do not select on this''.

• fq specifies ranges of frequencies. You can use strings with units (i.e. "800MHz"), or floats, in which case MHz is assumed.

• chan specifies ranges of channel numbers (1-based). Negative numbers can be used to specify channels starting from the end of the window, e.g., [-10,-1] means the last 10 channels.

• Where ranges are specified, the method expects either a 2N vector:
  [S₁, E₁, S₂, E₂,..., S_N, E_N]

  or a (2,N) array of start/end points.

  For example, if you want to indicate 7 channels (1,2,3,4,5,6,7), either chan = [1,7] or chan = [[1,2],[2,3],...,[6,7]] does the work.

  NOTE: The usual means of indicating a range with the ":" delimiter does not apply for the channel subexpression. For example, the equivalent to [1:3] to select channels 1 through 3 would be [1,3].

• Antennas can be specified by name or 1-based number (which is sometimes the same thing). Names must correspond to the ANTENNA subtable of the measurement set.

• Baselines may be specified either as an array of strings, using antenna names or numbers delimited by ``-'' (e.g. "1-2 4-7", or "RT1-RTA"), or as a (2,N) array of antenna numbers (e.g. [[1, 2],[4, 7]]).

The autocorr, timeslot+dtime, clip, flagrange and quack parameters specify what to flag (or unflag) within the selected subset, on a logical-OR basis. If none are specified, then the entire subset is flagged (or unflagged).

Clipping.

The clip and flagrange parameters enable flagging based on the value of an expression. Clip implies flagging of all values outside a specific range, flagrange implies flagging within a specific range. Like other flagging methods, you can specify values via expressions. Two types of expressions are recognized: correlation-derived expresisons (see the general autoflag module description for details), and UVW expressions (see below). To use a single expression and range, set clip or flagrange to a record as folows:

- af:=autoflag('3C273XC1.MS')
- af.setdata();
- af.setselect(clip=[expr='+ ABS XX YY',min=1e-6,max=.5]) 
# Above the feeds are assumed to be linear; use RR and LL for circular. 
- af.run();

The expr field specifies the expression to clip on, and min and max specify the range. Either the min or max field may be omitted, in which case $\pm$$\infty$ is assumed. To flag several ranges and/or expressions, set clip or flagrange to a record of records:

- af:=autoflag('3C273XC1.MS')
- af.setdata();
- cliprec:=[=]
- cliprec[1] := [expr='+ ABS XX YY',min=1e-6,max=.5]
- cliprec[3] := [expr='- ABS XX YY',max=.5]
- cliprec[2] := [expr="UVD",min=1]
- af.setselect(clip=cliprec)

A shorthand way is also available: use expression as the field name, and set the field to (a) a record of min, max, (b) a 2-element array of (min,max), or (c) a single scalar value (assumed to be max). Thus, the record above may be equivalently formed as:

- cliprec['+ ABS XX YY'] := [1e-6,.5]         # equivalent to [min=1e-6,max=.5]
- cliprec['- ABS XX YY'] := .5                # equivalent to [max=.5]
- cliprec['UVD']         := [min=1]            
- af.setselect(clip=cliprec)

When specifying several ranges for the same expression, you must naturally use the longhand form.

In addition to the regular correlation expressions, select also recognizes a few UVW-based expressions. The simplest ones are: U, V, W, ABS U, ABS V, ABS W. UVD stands for uv-distance, and corresponds to $\sqrt{u^2+v^2}$. Two more expressions represent angles in the uv-plane:

UVA

stands for uv position angle, specified in degrees clockwise from the v axis.

HA

stands for hour angle (East-West array assumed). It is specified in degrees counterclockwise from the u axis, using the following definition: u = Bcos$\alpha_{h}^{}$,    v = Bsin$\alpha_{h}^{}$sin$\delta$, where B is baseline, $\alpha_{h}^{}$ is hour angle, and $\delta$ is declination.

When using the UVA and HA expressions, you are actually defining sectors in the uv-plane, from min. to max. angle, e.g.:

- af.setselect(flagrange=[expr="uva",min=47,max=49])

...flags everything in the sector between 47 and 49 degrees, in terms of positional angle.

Quack

is a special option for VLA datasets, to flag the ``quacks'' at the beginning of each scan. It is specified by two numbers, [t_si,$\tau$]. t_si is the scan interval, used to determine the beginning of a new scan. $\tau$ is the number of seconds to flag at the start of a scan.

Arguments

spwid		Spectral window numbers (1-based), or [] or F for all
		Allowed:	Array of ints
		Default:	F
field		Field names or numbers (1-based), or [] or F for all
		Allowed:	Array of ints/strings
		Default:	F
fq		Range(s) of frequencies, or [] or F for all
		Allowed:	2N or (2,N) array of Strings w/units or floats
		Default:	F
chan		Range(s) of channels (1-based), or [] or F for all
		Allowed:	2N or (2,N) array of ints
		Default:	F
corr		Correlations (by name, e.g. ``XX YY''), or [] or F for all
		Allowed:	array of strings
		Default:	F
ant		Antennas (by name or number), or [] or F for all
		Allowed:	array of strings/ints
		Default:	F
baseline		Baselines, or [] or F for all
		Allowed:	array of strings/ints
		Default:	F
timerng		Time ranges, as MJDs or date strings, or [] or F for all
		Allowed:	array of strings/floats
		Default:	F
autocorr		Flag autocorrelations
		Allowed:	Boolean
		Default:	F
timeslot		Flag specific time slots. Specifies center time as MJDs or date strings
		Allowed:	array of strings/floats
		Default:	F
dtime		Tolerance of timeslot parameter, in seconds
		Allowed:	numeric
		Default:	10
clip		Flag values outside a specific range
		Allowed:	Record, see above
		Default:	F
flagrange		Flag values within a specific range
		Allowed:	Record, see above
		Default:	F
quack		Flag VLA quacks - scan interval and quack length, in seconds
		Allowed:	2-element numeric array
		Default:	F
unflag		Clear flags instead of setting them
		Allowed:	Boolean
		Default:	F

Example

- af:=autoflag('3C273XC1.MS')
- af.setdata();
# flag all autocorrelations and VLA quacks
- af.setselect(autocorr=T,quack=[120,60]) 
# flag some frequencies on specific antennas, during a certain period of time
- af.setselect(ant=[1,2,4],timerng="1998/01/20/20:00 1998/01/20/22:00",
               fq=[807.51,807.56])
# flag RR and RL on a few bad time slots on a specific baseline
- af.setselect(corr="RR RL",baseline="3-7",
               timeslot="1998/01/20/20:00:30 1998/01/20/20:20:30")