Public parameter group SCNSETS
This document contains an overview of the public parameter group SCNSETS, (part of) which is included in several NEWSTAR programs.
The document describes the individual parameters in alphabetical order. This description centers on the Help texts, which have been designed to guide the user to the proper choice at each junction, even if his knowledge of the overall workings of the program is only superficial.
Please note that the generic prompt and help texts defined for these parameters are frequently superseded in the actual applications by alternative texts that are more appropriate to the situation at hand. Unfortunately, the present architecture of NEWSTAR precludes the inclusion of such texts in the documentation system, so the only opportunity to read that information is during program execution (in your terminal window!).
Prompt: Detail level for overview (may vary per application)
Expected input: Character *10: 1 value
Specify the level for the overview.
To get a quick overview of the entire file, use
OBS Shows a summary per observation (2nd index) listing the type of
observation, the fieldname, the sequence number ('Volgnummer'),
project number and UT date and time and the breakdown in
numbers of fields, channels and sectors and polarisations
To get more other details (frequency, bandwidth, HA range, number of scans and number of interferometers), use
ALTOBS for one line per observation
FLD for one line per field in all observations
CHN for one line per channel in all fields in all observations
SCT for one line per sector in all channels in all fields in all
observations
NOTE: Depending on what is in your file, the volume of output in the latter three modes may be quite large. If you are not interested in the difference (e.g. in hour angle) between sectors, do not use SCT; if you are not interested in the differences (e.g. in frequency) between channels, do not use CHN.
There is presently no mechanism to select only specific groups or observations for display.
Prompt: 4th index: channels (may vary per application)
Expected input: Character *32: 1 value
Give the 'channel' index-range (chn) of a sector-Set
specification
(grp.obs.fld.chn.seq).
The standard use of multiple channels in a .SCN file field is for the different frequency channels or bands in an observation. Note that the index for the first channel is 1; channel 0 is by definition the 'continuum' channel, i.e. the sum of all the observed 'line' channels.
Possible answers ([]=optional):
0 take the continuum channel
n1 take channel nr n1 (n1=0,1,2,3,....)
n1-n2[:n3] loop over channels n1 through n2 [step n3]
* loop over all channels for the field (wildcard)
n1-[*] loop over all channels for the field,
starting with n1 [step n3]
NB: The associated SCN_LOOPS keyword allows even more looping over index values.
Prompt: 3rd index: fields (may vary per application)
Expected input: Character *32: 1 value
Give the 'field' index-range (fld) of a sector-Set specification
(grp.obs.fld.chn.seq)
The standard use of multiple fields in a .SCN file observation is for the different pointing centres (fields) in a mosaic observation.
Possible answers ([]=optional):
0 take first (or only) field
n1 take field nr n1 (n1=0,1,2,3,....)
n1-n2[:n3] loop over fields n1 through n2 [step n3]
* loop over all fields in the observation (wildcard)
n1-[*][:n3] loop over all fields in the observation,
starting with n1 [step n3]
NB: The associated SCN_LOOPS keyword allows even more looping over index values.
Prompt: 1st index: grp (may vary per application)
Expected input: Character *32: 1 value
Give the 'group' index-range (grp) of a sector-set specification
(grp.obs.fld.chn.seq)
An example of multiple groups in a .SCN file is one group for an observation and another one for the associated calibrator observation(2).
Possible answers ([]=optional):
0 take first (or only) group
n1 take group nr n1 (n1=0,1,2,3,....)
n1-n2[:n3] loop over groups n1 through n2 [step n3]
* loop over all available groups (wildcard)
n1-[*][:n3] loop over all available groups,
starting with n1 [step n3]
NB: The associated SCN_LOOPS keyword allows even more looping over index values.
Prompt: Loop specifications: |- (may vary per application)
Expected input: Character *32: 1 to 16 values
Quick reminders: ===============
- L gives you a quick summary of the groups in your .SCN file
- O gives you access to more detailed overviews in various levels of detail
- #<n> is a synonym for the grp.obs.fld.chn.seq index that is sometimes
convenient to use. # ('absolute') sector numbers are shown in most
displays that show sector indices.
- A loop is specified by the number of cycles and the index increment per
cycle. Loops may be nested.
The loop concept in full: ========================
A loop specifies repeated execution of your operation. It is defined by
the number of cycles and the increment per cycle for the sector indices:
<n_cycle>, <grp_incr>.<obs_incr>.<fld_incr>.<chn_incr>.<seq_incr>
Later you will define, through the SCN_SETS parameter, the sector set to be
processed in the first cycle.
Example:
SCN_LOOPS= 3, 0.0.2.1.0
SCN_SETS= 2.*.0-2.3.0, 2.*.1.
requests your operation to be executed three times, with sector sets
2.*.0-2.3.0 (SCN_SETS value)
2.*.2-4.4.0 (SCN_SETS + 1*increment)
2.*.4-6.5.0 (SCN_SETS + 2*increment)
In the increment value, 0s and trailing dots may be omitted. Negative increments are permitted.
Loops may be nested by giving more than one cycles-increment pair; in this case
the rightmost loop is executed inside the loop to its left.
Example:
SCN_LOOPS= 2,.1, 2,..1
SCN_SETS= 0.0.0.*.0
results in your operation being performed on the following sequence of
sectors:
0.0.0.*.0
0.0.1.*.0
0.1.0.*.0
0.1.1.*.0
Some fine points: ================
Loops are a useful shorthand for specifying complicated repetitions of
the same operation on different sector sets. As the examples above demonstrate,
using SCN_LOOPS can save a lot of typing, in particular if the number of cycles
is large.
Note that each cycle of a loop starts the requested operation anew. To
understand what this means, consider two ways to process all fields of a
16-field mosaic observation:
SCN_LOOPS=<no input> SCN_LOOPS=16,..1
SCN_SETS=grp.obs.* SCN_SETS=grp.obs.0
The left specification requests a single pass thorugh the operation using all
fields as input. The right specification requests 16 passes successively using
fields 0,1,2,... as input.
Prompt: 2nd index: observations (may vary per application)
Expected input: Character *32: 1 value
Give the 'observation' index-range (obs) of a sector-Set
specification
(grp.obs.fld.chn.seq)
Example of multiple observations in one ..SCN file group are:
the parts of an interrupted 12h observation;
observations of the same object, with different array configurations.
Possible answers ([]=optional):
0 take first (or only) observation
n1 take group nr n1 (n1=0,1,2,3,....)
n1-n2[:n3] loop over groups n1 through n2 [step n3]
* loop over all available observations (wildcard)
n1-[*][:n3] loop over all available observations,
starting with n1 [step n3]
NB: The associated SCN_LOOPS keyword allows even more looping over index values.
Prompt: 5th index: sectors (may vary per application)
Expected input: Character *32: 1 value
Give the 'sequence number' index-range (seq) of a sector-Set
specification
(grp.obs.fld.chn.seq).
A standard use of multiple sectors for one .SCN file field and one frequency is for the different hour-angle 'slices' in a mosaic observation.
Possible answers ([]=optional):
0 take the first sector
n1 take sector nr n1 (n1=0,1,2,3,....)
n1-n2[:n3] loop over sectors n1 through n2 [step n3]
* loop over all
(wildcard)
n1-[*] loop over all sectors for the field and channel,
starting with n1 [step n3]
NOTES:
In a mosaic observation, the HOUR_ANGLE range parameter can be used to
select sectors. This is simpler but cruder: The same range applies to all
SCN_SETS and SCN_LOOPS specified.
The associated SCN_LOOPS keyword allows even more looping over index
values.
Prompt: Sectors to process: grp.obs.fld.chn.seq (may vary per application)
Expected input: Character *32: 1 to 64 values
Quick reminders: ===============
- L gives you a quick summary of the groups in your .SCN file
- O gives you access to more detailed overviews in various levels of detail
- #<n> is a synonym for the grp.obs.fld.chn.seq index that is sometimes
convenient to use. # ('absolute') sector numbers are shown in most
displays that show sector indices.
- or > will prompt you for each of the 5 indices separately. use this
option if you are not yet comfortable with the sector-indexing system.
- If you have requested looping (SCN_LOOPS parameter), the sectors you
specify will be processed in the first loop cycle, and the indices
incremented for each following cycle.
- If you have second thoughts about looping, reply # or ctrl-D to backtrack.
Sector selection: ================
You may select SETS of sectors for processing by [ranges of] values for
the five indices. A range has the form <start>-[<end>][:<step>]. A wildcard '*'
means 'all'; *s and trailing dots may be omitted.
Example
. 3-7:2 . 4-:2 . 1-7 (blanks inserted for clarity only)
meaning
all grp (missing grp index is replaced by a '*')
for each grp: obs=3 to 7 in steps of 2 (i.e. 3, 5 and 7)
for each obs: all even fld starting at 4
for each fld: chn=1 to 7;
for each chn: all seq (omitted trailing seq index replaced by a '*')
Multiple SETS may be specified, separated by comma's: <Set1>,<Set2>,... The associated SCN_LOOPS keyword allows even more looping over index values.
Other keywords allow the user to select hour-angle range, polarisation and interferometers within each SECTOR.
Explanation of sector indices: =============================
A .SCN file contains visibilities and associated data for one or more
objects. The basic unit of data is the SECTOR, which is a collection of SCANS
contiguous in hour angle for one sky position and one frequency. Sectors are
addressed through a SECTOR INDEX which is a string of five integers separated
by dots:
grp.obs.fld.chn.seq
The GROUP (grp) and OBSERVATION (obs) are basically administrative units for
organising the data, e.g. per object. grp and obs number alocations have
been determined by NSCAN when you read the data in.
Mosaic observations contain multiple FIELDs (fld), numbered from 0 to n-1 in
the sequence in which they were observed at the WSRT. A non-mosaic
observation contains only field 0.
Line and broadband continuum observations generally have several frequency
CHANNELS (chn), also known as 'bands'. The channles are numbered from 1 to
N. Channel 0 is by definition the 'continuum' channel, i.e. the sum of all
'line' channels.
In mosaic observations, the sector SEQUENCE (seq) number distinguishes the
successive hour-angle 'sectors'. Other situations are conceivable where
multiple sectors with the same grp.obs.fld.chn exist; it is then your
responsibility to know what they represent.
Index values start at zero. (Remember that for the CHN index this is the continuum channel.)
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