AIPS HELP file for FITLD in 31DEC21
As of Fri Feb 26 3:18:57 2021
FITLD: Task to store an image or UV data from a FITS tape
INTAPE 0.0 9.0 Input tape drive # (0 => 1)
NFILES -9999.0 9999.0 # of files to advance on tape
DATAIN Disk file name
OUTNAME File name (name)
OUTCLASS File name (class)
OUTSEQ -1.0 9999.0 File name (seq. #)
0 => highest unique number
=> matching (on VLBA)
-1 => FITS tape value
OUTDISK 0.0 9.0 Disk drive # (0 => any)
OPTYPE Type of data to load,
' ' => all types
'UV' => UV data
'IM' => images
NCOUNT 0.0 9999.0 Number of files to load.
DOTABLE -1.0 1.0 True (1.0) means load tables
DOUVCOMP -1.0 1.0 >0 => compressed data (FITS)
DOCONCAT -1.0 1.0 >0 -> if VLBA correlator data
append data to existing
files, or if no appropriate
files exist create a new file
and append all data to that
DOKEEP -1.0 1.0 > 0 -> keep fully flagged
NPIECE 0.0 90.0 Maximum uv table piece to
load (ignored for tape unless
NCOUNT = 1)
ERROR -1.0 3.0 >= 2 -> do not use AIPS
history in the FITS file
Following adverbs are useful
only when reading VLBA IDI
CLINT CL entry interval (min)
0 => 1 minute.
SOURCES Source list to accept.
QUAL -10.0 Source qualifier -1=>all
TIMERANG Timerange selected
BCHAN 0.0 8192.0 Lowest spectral channel
number to select in each IF.
ECHAN 0.0 8192.0 Highest spectral channel
number to select in each IF.
BIF 0.0 100.0 Lowest IF number 0=>1
EIF 0.0 100.0 Highest IF number 0=>all
DIGICOR -1.0 4.0 Controls the application of
the VLBA and DIFX correlator
0,1,3 => perform corrections
2,4 => perform cross-power
corrections, do total-power
only if zero padding used.
-1 => do NOT perform
3,4 => do even if not VLBA
SEE HELP for more details
REFDATE Reference date. 'yyyymmdd'
before or = the obs date
' ' => the obs date
SELBAND Bandwidth to select (kHz)
SELFREQ Frequency to select (MHz).
FQTOL Frequency tolerance assigned
to SELFREQ, FITLD will select
data with freq. of SELFREQ
The unit of FQTOL is kHz.
<=0 => 10 kHz
WTTHRESH Flagging threshold based on
weights. See HELP.
0 => no flagging
1 => will flag ALL data
DOWEIGHT > 0 => scale weights by
OPCODE Specify if wish to keep VT
(VLBA Tape Statistics) table
and other tables. See HELP.
' ' => do not save tables
ANTNAME List antenna station names in
desired order (IDI data only)
'VLBA', 'VLITE' are special
Use: FITLD loads both maps and UV data from tape (or disc) to disc. It
will only load FITS files, if any other type of file exist on the
tape the task will fail, so users must skip over non-FITS files.
The aim of this task is to read, in one pass, a tape written by
FITTP or FITAB. However a user may specify that all 'UV' files
are to be loaded, or all map files, or (default) all types of
FITS file. If IMAGE extensions are present, they are written to
separate catalog entries, but all TABLES are attached to the
primary catalog entry. They may only occur with a real or empty
image in the main FITS HDU.
FITLD reads standard images and uv data from FITS files and also
translates FITS-IDI files. This last is normally written by
correlators rather than post-processing software and requires
additional adverbs not honored by the other portions of FITLD.
Until the end of July 1999, UV data sets written out with FITAB,
read back in with UVLOD or FITLD, processed, and then written out
with FITTP could contain AIPS history records which will define
the data set falsely to the standard reading tasks in AIPS. If
you attempt to read a data set or image with FITLD (NOT a VLBA
correlator data set) and encounter error 4 (premature end of file)
or other failure, try reading the FITS data set with PRTTP with
ERROR set to 2. If this works, use UVLOD for UV data and IMLOD
for images with ERROR=2.
FITLD (and IMLOD, UVLOD, PRTTP, TPHEAD) now understand and
interpret the standard world coordinate system keywords CDi_j
and PCi_j. They are used if possible and problems reported.
INTAPE......The input tape drive #. 0 => 1.
NFILES......# of files to skip on tape before reading data. For
example, 1 => start of next file, -1 => start of previous
file. 0 => no tape movement at all. (AIPS verbs AVFILE
plus TPHEAD allow you to position and check the tape in
advance; be sure to reset NFILES to 0 for FITLD after
DATAIN......48-character name of the disk file from which to read a
FITS file. It must be in the form
where is the remote computer name, is the
environment variable (logical name) for the disk area in
which the file named is stored. is
usually omitted when the file is local to the current
computer. If DATAIN is not found, the task will try
DATAIN with the character 1 appended.
Beginning 2003-Oct-16 FITLD can read more than one disk
file at a time. In that case, they must all have the
same name except that the last letter(s) are the
sequence number 1 through NCOUNT with no leading zeros.
DATAIN must give the base name only, omitting the
sequence number. Then either
DATAIN = 'MYDATA:file_
DATAIN = 'MYDATA:file_1
can access files in $MYDATA named file_1, file_2,
file_3, etc. Note that this is similar to the pieces of
a FITS pieced UV-table data set, but only one UV-table
data set may be read at a time.
OUTNAME.....The output filename (name). Standard behavior with
default = the original file name (FITS), the source name,
OUTCLASS....The output filename (class). Standard behavior with
default = the original map class (FITS) or a class of the
form 'STYP ', where S = (I, Q, U, V) Stokes parameter of
the image and TYP = (BEM, CLN, MAP) for a beam, clean map,
or anything else. Special combination images (OPTD et
al.) are also recognized.
OUTSEQ......The output filename (seq #). 0 => Find the lowest number
which produces a unique mapname. -1 => use the sequence
number on the tape (if any - works only on tapes written
by FITTP). SEE ALSO the remarks below under DOCONCAT.
OUTDISK.....The disk drive #. 0 => highest with space
OPTYPE......The type of data files to load, ' ' (default) => load uv
and images; 'UV' => load uv files only; 'IM' => load
NCOUNT......The number of consecutive files to load from tape or
disk. 0 -> 10000 for tape data, 0 -> 1 for disk FITS
files, but it is better to give a correct number to
allow the program to manage messages, file status, etc.
If you want to load only up to NPIECE pieces of a uv
table set, then NCOUNT must be 1 (or 0 if disk since
that defaults to 1). Note that the multiple pieces of a
uv-table set are counted as 1 for the purposes of NCOUNT
(but not NFILES).
DOTABLE.....True (1.0) means load all tables. (FITS images only, all
tables are loaded for UV data and IDI files).
DOUVCOMP...If true (DOUVCOMP > 0) the output data is written in
compressed format which can result in a substantial
reduction in disk space needed. This causes some loss of
spectral dynamic range and allows one bad channel value
to destroy all the good data; the numbers are stored as
integers of value -32767 to 32767. Real differences in
weights between IFs, polarizations, and spectral channels
within a record are also lost. Only used for FITS files
of the random-groups type (e.g. written by FITTP or CASA
exportuvfits) and those written in the IDI convention for
binary tables. Binary tables such as those written by
FITAB have the compression selected by the compression
state of the table. Not used for images.
DOCONCAT...If true (>0) and the input data are VLBA binary tables
(IDI directly from the correlator) then data are to be
appended to an existing file if possible. Possible
output files can be selected by OUTNAME, OUTDISK and
OUTSEQ. Use this option with CAUTION; it is REQUIRED (to
be true) if you wish to concatenate the data from
multiple files being read in the same execution of FITLD
for VLBA correlator data. (UV table pieces from FITAB
are concatenated to each other even if DOCONCAT is false.)
If DOCONCAT is false and OUTSEQ is specified, FITLD will
fail at the start of file 2. If DOCONCAT is false and
OUTSEQ is not specified, then FITLD will make separate disk
files for each tape file. These disk files may be
concatenated later with DBCON, but perhaps only after
they have been MATCHed. FITLD will write one or, if it
finds data that do not match in e.g. number of channels,
more output files. If DOCONCAT is TRUE then FITLD will
look over all files matching the OUTNAME, OUTCLAS,
OUTSEQ, OUTDISK parameters to try to find one that it can
append data to. If it does not it will create one based
on these name parameters. That will generally fail if
OUTSEQ is specified. Thus, for DOCONCAT true, set
OUTSEQ=0. Be very careful if specifying ANTNAME with
DOKEEP.....> 0 -> keep any fully flagged vis records. Otherwise
they are not copied from the input file. They are
counted and reported in any case.
NPIECE.....Maximum piece number to read in a multi-piece uv-table FITS
data set. 0 => maximum in the data. Note, if NCOUNT > 1,
NPIECE is set to 999 by FITLD.
ERROR......>= 2 => do not parse AIPS history cards found in the FITS
header. Do not use this option until you have tried IMLOD
without it. If you get mysterious errors (usually error 4
which implies premature end of file), then try IMLOD with
ERROR set to 2. For a period of time, UV data sets written
out with FITAB, read back in, processed, and then written
out with FITTP could have so many AIPS history records in
their header as to cause IMLOD to read the data wrongly.
This can also occur when AIPS data are written to another
package and then brought back to AIPS.
The following adverbs apply only to FITS-IDI data files
which generally are written by VLB correlators rather than
post-processing software. The VLITE project of the VLA also
uses VLB-like files.
CLINT......IDI only: To define the interval between CL entries for
antennas for data from the VLBA correlator only. This
defines the fundamental time-scale for calibration, 1
minute is a good value for most frequencies. Shorter
intervals may be relevant for high frequency programs.
SOURCES....IDI only: Source list. List of sources to accept from
the VLBA distribution tape (or files).
QUAL.......IDI only: Only sources with a source qualifier number in
the SU table matching QUAL will be used if QUAL is not -1.
TIMERANG...IDI only: Range of UTC times to be read wrt the first day
number in the first file read. 0=>all.
BCHAN......IDI only: First spectral channel number to select from
each IF. 0=>1.
ECHAN......IDI only: Highest spectral channel number to select from
each IF. 0=>all higher than BCHAN.
BIF........IDI only: First IF to copy. 0=>1
EIF........IDI only: Highest IF to copy. 0=>all higher than BIF.
WARNING: IF selection will work differently in FITLD
where it is based on the input IF numbers and in later
tasks where it is based on IF numbers reordered by FITLD
to frequency order. These two selections will be the
same only if the data from the correlator are in
increasing frequency order.
DIGICOR....IDI only: Data processed in digital correlators such as
the VLBA correlator and DiFX are affected by a variety of
phenomena that we collectively refer to as digital
effects. FITLD is able to apply the corrections needed to
scale the data to the values that would be returned by a
purely analogue correlator. DIGICOR = -1 will turn off
the application of these correction, DIGICOR = 0 or 1
will apply them to both cross and total power, DIGICOR =
2 will apply the corrections to cross-power and only to
total power if zero-padding was used in the correlator.
The latter case is designed to deal with a situation in
which the total-power spectrum is dominated by multiple,
strong spectral lines. In that case, if zero-padding was
not used, the reconstructed total-power spectrum, after
an FFT, is inaccurate at some level. In all continuum
cases DIGICOR = 1 should be the default. In nearly all
line cases DIGICOR = 1 is fine. only if the Tant in the
line is about equal to the Tsys should DIGICOR = 2 be
used. One word of caution, for data correlated prior to
Aug 1 1994 the correlator was incorrectly scaling the
data by a factor of 1.57 (i.e. PI/2) . So for that data,
DIGICOR can be used but a BFACTOR of 0.6369 (i.e. 1/1.57)
should be applied in APCAL or to the final images.
Unfortunately FITLD had no knowledge of the date of
correlation so cannot perform this correction. The code
detects data from the DiFX correlator and applies a
different (1.0) saturation correction in that case.
Actually, 1.0 is used for all but the VLBA (array=VLBA
and correlat ' ' or 'VLBA'),
**** FITLD will do corrections for arrays other than
**** VLBA only if DIGICOR is set to 3 or 4.
REFDATE....IDI only: Reference date 'yyyymmdd' ('dd/mm/yy' accepted
but deprecated), ' ' => first found
Better get it right - a date after the reference date in
the data will cause the data to fail to load.
SELBAND....IDI only: Bandwidth of data to be selected. If more than
one IF is present SELBAND is the width of the lowest
frequency IF required. Units = kHz, 0=> all
SELFREQ....IDI only: Frequency of data to be selected. If more than
one IF is present SELFREQ is the frequency of the lowest
frequency IF required. FITLD will sort the IF channels
into increasing frequency order as the data are read from
the tape so all selection will be performed on the
frequency and bandwidth values of the output IF 1.
Units = MHz, 0=> all
FQTOL......IDI only: The frequency tolerance used in selecting data
using SELFREQ. Data whose output IF 1 frequency lies in
the range SELFREQ +/- FQTOL will be read. Units = kHz,
=< 0 => 10kHz
WTTHRESH...IDI only: Weight based flagging threshold. If WTTHRESH
> 0 the weights for each visibility are examined. If
weights for all IFs are =< WTTHRESH the visibility record
is flagged. The flagging is permanent, i.e. the record is
not copied to the output file.
If a weight of some IFs (not all) =< WTTHRESH such
visibilities are recorded, but the weight of these IFs is
put to zero (flagged). Input weights lie between 0 and
1. If you wish to apply weight based flagging a suggested
value for WTTHRESH is 0.8. A value of 0 switches off the
DOWEIGHT...> 0 => (IDI only) scale the weights by the product of the
integration time (sec) and the channel bandwidth
(Hz). This will make the data weights be sensible
when the amplitude calibration is applied, i.e.
more or less 1/sigma^2 in 1/Jy^2.
<= 0 => Data weights stay as they are in the IDI file.
After calibration they will be on the order of
OPCODE.....IDI only: By default, the input tables that are
translated into AIPS tables are all removed and the large
VT (VLBA Tape Statistics) table is neither translated nor
saved. If you wish to keep the former and/or latter enter:
'VT' => Keep VT tables, not the rest
'ALL' => Drop VT tables, keep rest
'VALL' => Keep VT and other tables
ANTNAME....With FITS-IDI files, the antennas acquire antenna numbers
in the order in which they are encountered in reading
the input files. To select a specific order (to force
the same antenna numbers with different data sets), you
may specify the antenna/station names in the desired
order. The special string VLBA is converted to 10 names
'BR', 'FD', 'HN', 'KP', 'LA', 'MK', 'NL', 'OV', 'PT',
and 'SC'. Any antenna not in the list will be added to
the end of the list as it is encountered.
The special string VLITE will generate the list 'V0',
If you are concatenating, make sure this list applies to
the pre-existing file. The list will be used during
concatenation if it can be. Note that lists starting
with VLBA or VLITE will only look for those antennas
during concatenation. Any others in ANTNAME will be
FITLD: Task to load FITS format data
Documentor: Chris Flatters
Related Programs: FITTP, FITAB, IMLOD, UVLOD, TAMRG
Disk file reading: DATAIN
To read multiple disk files in one pass of FITLD, the file names must
all be predictable from the user supplied value of DATAIN. This
requirement has led to the requirement that they be named with a
consecutive postfix number beginning with 1. It may seem onerous to
have to do this, so we suggest using link files. Thus 4 disk files of
consecutive VLBA correlator data may be linked to a simple name in the
local directory ($MYWORK) by
primate<142>$ ln -s /home/euro/aipsdvlp/WB/AO-0/32400001.FITS Lorant_1
primate<143>$ ln -s /home/euro/aipsdvlp/WB/AO-0/32410001.FITS Lorant_2
primate<144>$ ln -s /home/euro/aipsdvlp/WB/AO-0/32420001.FITS Lorant_3
primate<145>$ ln -s /home/euro/aipsdvlp/WB/AO-0/32430001.FITS Lorant_4
Then, inside AIPS, one sets
NCOUNT = 4; DATAIN = 'MYWORK:Lorant_
where you should note (a) DATAIN= is the last command on the line and
is typed with no close quote so that the case is preserved, (b) the
number 1 may be left off the name (FITLD will append it), and (c) the
environment vaiable $MYWORK must be known before AIPS is started and
is typed with a colon following but no $.
VLBA CALIBRATION TRANSFER
FITLD will load flags, gain curves, system temperature data, and
pulse-cal data from VLBA format FITS files. These data will be
loaded into version 1 of the FG, GC, TY, and PC tables
If several input files are concatenated into one AIPS file then
the FG, GC, TY, and PC tables will contain the calibration data
from all of the inputs files that were concatenated. This may
lead these tables containing duplicated records.
I recommend that you remove all of the duplicate records in the
GC, TY, and PC tables after you have loaded all of the data for
a given experiment using the procedure MERGECAL (see HELP
KNOWN DEFICIENCIES WITH RESPECT TO INTERFEROMETRY DATA
FITLD assumes that the reference date for the data loaded from
FITS-IDI files is the first reference date encountered in any
of the tables in the file. If the file conforms the the table
ordering conventions in AIPS Memo 102 then this should be the
reference date for the ARRAY_GEOMETRY table for the first
array. This is normally the correct reference date.
If any table has a reference date (RDATE) earlier than that
chosen by FITLD or if data occur before 0h on the chosen
reference date then AIPS may not be able to handle the data
output by FITLD.
It is also possible for problems to occur if the first table
in the file that has an RDATE keyword is not an ARRAY_GEOMETRY
table and the value of that keyword differs from the RDATE of
of the first ARRAY_GEOMETRY table since the reference date
will not then be the same as the reference date for subarray
1 as is assumed in some parts of AIPS.
This adverb has been removed and made always true. It is turned off
for correlators other than the VLBA.
DELCORR....This parameter determines whether the second order
amplitude corrections caused by delay decorrelation
in the VLBA correlator can be applied after fringe
fitting or not. These corrections are necessary for
obtaining extremely high dynamic range images. If
they are not applied excellent images can still be
obtained. The corrections are applied when a CQ
table is attached to the data, the CQ table
contains information required to perform the
correction - see AIPS Memo 90 by Athol Kemball for
more details. Under some circumstances (e.g.
spectral averaging in the correlator on data that
contains narrow spectral lines) the assumptions
under which the 2nd-order corrections can be
applied are false. In that case the CQ table should
not be generated.
DELCORR = -1 => do not generate CQ table
DELCORR >= 0 => generate CQ table.