AIPS HELP file for VLAC in 31DEC20
As of Sat Feb 22 16:11:01 2020
VLAC: Calibration verification/timing test.
TCODE INIT, TEST, READ, or WRIT
TMODE 'T' or 'M' inputs
TMASK 1.0 127.0 test selection bit mask
DDISK 1.0 9.0 Disk drive #: master UVDATA
MDISK 1.0 9.0 Disk drive #: other masters
TDISK 1.0 9.0 Disk drive #: test images
IOTAPE 0.0 9.0 Input/Output tape drive #.
DDTDISK Disk area for READ and WRIT
EDGSKP 0.0 64.0 Pixels to skip at edges
TERSE -1.0 10.0 > 0 => reduced output
DOCRT -1.0 132.0 > 0 => output on terminal
> 72 => width of terminal
Printer disk file to save
BADDISK Disks to avoid
Type: RUN file
Use: VLAC performs the AIPS verification test for continuum calibration
software. See RUN files VLACLOAD.001 and VLACEXEC.001. The
purpose of the inputs file is to perform bounds checks on the
parameters and to enable the use of TPUT and TGET.
TCODE String*4 'INIT', 'TEST', 'READ', or 'WRIT'
TMODE String*1 'T' or 'M' inputs for SPLIT, IMAGR
TMASK Scalar test selection bit mask (1-127)
DDISK Scalar Disk drive # (1-9) master UVDATA
MDISK Scalar Disk drive # (1-9) other master files
TDISK Scalar Disk drive # (1-9) test files
IOTAPE Scalar Input AND output tape drive #. (1-9)
DDTDISK String*8 Logical name of disk area to be used for
FITS-disk files in READ or WRIT instead of
actual magnetic tape.
' ' => use magnetic tape.
EDGSKP Scalar Number of pixels to skip at edges in comparing
test and master images
TERSE Scalar > 0 => reduced output:
> 0 = drops INPUTS for all tasks and TPHEAD
when reading tape
> 2 = also drops CATALOG listings
> 3 = also drops IMHEADER listings
Use 0 on all new or uncertain systems.
DOCRT Scalar <= 0 -> print the messages and output from tasks
on the line printer.
> 0 -> show the messages and output from tasks
in slightly abbreviated form on the terminal.
If you have a wide terminal, set DOCRT to its
width in characters for a more complete
OUTPRINT String*48 Disk file name in which to save the line printer
output. ' ' => use scratch and print
immediately for interactive jobs - batch jobs
use OUTPRINT = 'PRTFIL:BATCHjjj.nnn' (jjj = job
#, nnn = user #). When OUTPRINT is not blank,
multiple outputs are concatenated and the file
is not actually printed.
BADDISK Array Disks to avoid for scratch files.
VERSION String*48 OLD,NEW,OLDPSAP,NEWPSAP,LOCAL
(also private dirs; use | to separate)
VLAC runs in four different modes: (TCODE)
INIT = starts from the original master UV dataset, and (re)computes
master files (does ALLDEST). The "mask" TMASK controls which
TEST = re-does the INIT computation but stores the new files under
different names and compares against masters. The "mask"
TMASK controls which steps execute. For the early, table
manipulation steps, the TEST mode can only operate on the
output of the previous step and step 1 must be run first.
For the SPLIT and IMAGR (32 and 64) tests either the TEST run
output of the previous step (TMODE=T) or the INIT run output
(TMODE=M) can be used as input.
WRIT = write out all master files to tape or pseudo-tape FITS disk.
READ = read in all master files from tape or pseudo-tape FITS disk.
A binary mask controls which steps of the test execute:
TMASK +1=>UVCOP, +2=>UVFLG,SETJY, +4=>CALIB, +8=>GETJY,CLCAL,
+16=>PCAL,CLCOR, +32=>SPLIT, +64=>IMAGR
For example, TMASK=54 would execute UVFLG&SETJY, CALIB, PCAL&CLCOR and
SPLIT. Note: the UVCOP step is required once to the create the input
file for the following steps for TCODE='TEST'.
Explanation of VLAC: (WDC Sep90)
VLAC is designed to verify the correct functioning of the continuum
calibration using a test set of VLA observations. All of the typical
steps in editing and calibrating a set of continuum (non-VLBI) are
exercized except for interactive editing. Since most of these operations
modify only tables, a comparison of selected portions of various of the
calibration tables is made. After the calibration tasks are completed,
the data is calibrated using SPLIT and the uv data is compared with the
master version. The final test is a comparison of images made from the
Steps to execute the VLAC Test on a new computer:
1. Log in to AIPS under the user number which will own the data files
and the SAVE/GET files associated with the test. It is probably
convenient to clear your AIPS message file before proceeding:
PRNUM=-1; (PRTMSG possibly) ; CLRMSG
2. Now do the POPS command "RUN VLACLOAD". This initiates the
compilation process, which can take as long as 15 minutes on a
heavily loaded VAX-11/780. You may want to execute the POPS command
"PRTMSG" afterwards to document the compilation of the test
3. The next step is to read the data files from the tape. There are 6
files for this test. The read process consists of the following
CLRMSG (prepare for tape read steps)
Specify DDISK, MDISK, TDISK, and IOTAPE
DDTDISK = ' ' for real tapes
Also specify BADDISK as needed
TCODE='READ'; TPUT VLAC (TPUT saves adverb values)
MOUNT the tape
DISMOUNT the tape
The READ mode of VLAC will execute FITLD to read the UV and map files
to disk. At the end of the process, it rewinds the tape and prints a
directory of the disk files.
Alternately, if you have the files on disk, merely set the DDTDISK
adverb to point at where the files reside (you need to define or use
a "logical" or environment variable with an uppercase name before
starting AIPS to use this feature; e.g. FITS).
NOTE: VLACEXEC will insist on having non-default values for
IOTAPE, DDISK, MDISK, and TDISK.
4. Now it is time to actually perform the test. The 'TEST' mode
recomputes the various files. All map, uv data and selected
calibration table results are compared to the master versions which
were read from tape in the previous step. The steps are:
CLRMSG (prepare for test results)
TPUT VLAC (saves the adverb values)
The message file from VLACEXEC will be more than 2000 lines long. It
is intended to be the major item documenting the test procedures and
results. Several tasks will print results rather than put them in
the message file. Especially, the LISTR output should be checked.
5. The 'WRIT' mode tests task FITTP, while 'READ' tests FITLD. The
basic idea is to produce a tape, and then to read that tape on an
AIPS system to verify that it yields correct results. It follows
that generating a new tape with the 'WRIT' mode and then executing
'READ' and 'TEST' on it will also effectively test the tape tasks.
Better yet, take the tape to another AIPS and run VLAC on it! This
verifies the intercommunication of the systems.
The steps are:
DDTDISK = ' ' for real tapes or DDTDISK = 'yourarea' for disk
Note that when we say "tape", we mean either magnetic tape in the
usual sense, or pseudo-tape disk files. The latter are selected by
setting DDTDISK to a non-blank value which is the logical name
(environmental variable) for the disk area to be used. The disk
files are given a fixed and obvious pattern of names (VLACnnnnnn,
where nnnnnn is the image name related to the task name).
6. Finally, one wants to know the accounting statistics from the test
runs. The accounting listing can be correlated with the message file
listings in order to analyze the performance of the tested system.
VLAC now runs task PRTAC to produce the desired information. Note
that PRTAC has exclusive access to the accounting file until it
finishes, and so various tasks may complain while they are waiting to
get access to the file.
The listing produced by PRTAC will have one line for each execution
of any task or program AIPS. The columns of the listing give the
taskname, POPS#, user#, start-time, real-time, CPU-time, and "IOCNT".
Asterisks mark any run that aborted. After this basic sequential
listing comes a listing by task name giving the totals accumulated by
each task. The listing is given in two sort orders.
The tasks tested in some modes are: FITLD, FITTP, UVCOP, TABED,
UVFLG, SETJY, CALIB, TASRT, TASAV, GETJY, CLCAL, PCAL, TACOP, CLCOR,
LISTR, SPLIT, UVDIF, IMAGR, and COMB
Description of Data Calibration Test
The test data set consists of observations of a phase calibrator over
a period of 4 hours to get a spread of parallactic angle for
polarization calibration, a scan of 3C286 to calibrate the flux density
and the polarization orientation and slightly over an hour of program
source data. The data were obtained with the VLA in "A" configuration
at 3.6 cm wavelength and 12.5 MHz bandwidth. The data contains two IFs
and RR, LL, RL and LR polarization correlations. Tha master copies of
the files were computed on s prerelease version of 15JAN91 AIPS on a Sun
The following sections describe in some detail the tasks run in each
of the test steps. Only the test mode is described; READ, WRIT and INIT
modes are fairly obvious given the TEST mode operation.
Step 1. The master uv data file is copied to a test version using
Step 2. Bad data are flagged with several runs of UVFLG. The fluxes in
the SU table are reset and the flux of 3C286 set using SETJY. TABED is
used to correct the flux of 3C286 for the appropriate UVRANGE.
Step 4. CALIB is run on 3C286 and the phase calibrator. The SN table
is sorted using TASRT and the tables are copied using TASAV. The
comparison of the SN tables is done using the TASAV version.
Step 8. GETJY is used to estimate the flux density of the phase
calibrator and corrects the SN table. CLCAL then filters the SN table
with a 1.1 hour median window filter on the amplitudes and writes CL
table 2. Comparisons are made of the SU and CL #2 tables.
Step 16. PCAL is used to determine the instrumental calibration and the
polarized flux of the phase calibrator. If TERSE is less than 3 then
LISTR is used to give a matrix listing of the polarized flux of 3C286.
TACOP and CLCOR are used to correct the AN and CL table #3 for the
right-left phase difference. Comparisons are made of the AN
(polarization parameters), SU (polarized flux) and CL #3 tables.
Step 32. SPLIT is used to apply the calibration and editing tables to
the source data and write a single source output file. This file is
compared with the master.
Step 64. IMAGR is run on the output of SPLIT to make I and Q images.
Comparisons are made of the I image, I beam and the Q image.
Interpretation of Test Results
The results of the mapping and table tests are recorded as the number of
BITS of accuracy. The BITS of accuracy are defined in two ways, by the
MAX difference in the Master image and the Test image and by the RMS
differences in the images. The BITS measured by the the base 2
logarithm of the ratio of PEAK and DIFFERENCE of the images.
The BITS are calculated as -3.3219 * LOG(DIFF/PEAK). (LOG is the Base
10 Logarithm; 1/LOG(2) = 3.3219)
The expected BITS of accuracy for the tasks are in the range of 10 to 20
BITS. The RMS BITS of accuracy is always greater than the PEAK BITS of
accuracy. Perfect agreement will be reported as 99 bits agreement.
Note that some of the operations in this test modify the input file(s).
This especially true for the table operations and in particular GETJY
may recursively modify the SU and SN tables. This may cause roundoff
errors to accumulate. For the most accurate test, all of the steps must
be run in order exactly once each (i.e. use TMASK=127).
Note also that the uv data is stored in compressed form meaning that it
has at most 15 bits of precision rather than the 24-25 (usually) for
There are three kinds of test made of agreement with the master data:
1) UV data sets are compared using UVDIF which reports on individual
visibility records with differences larger than the threshold. The
statistics of the data being checked are also reported.
2) Images are differenced and the statistics of the difference image is
reported both as the test is done and in the summary at the end.
3) Selected portions of calibration tables will be compared with the
master version and differences are reported in a manner similar to that
The following describes the comparison tests between tables, uv data
and images. The column labeled "Test" gives the label used in the
summary given at the end of the execution of VLACEXEC.
Test Type Comments
__________ ____ _______________________________________________________
CALIB SN 1 tab The real part of IF 1, RCP of the SN table produced by
CALIB is compared.
CALIB SN 2 tab The imag part of IF 2, LCP of the SN table produced by
CALIB is compared.
GETJY tab I flux from SU table determined by GETJY.
CLCAL CL 1 tab The real part of IF 1, RCP of the CL table produced by
CLCAL is compared. Every 25th element of the table is
CLCAL CL 2 tab The imag part of IF 2, LCP of the CL table produced by
CLCAL is compared. Every 25th element of the table is
PCAL AN tab The third polarization constant for LCP in the AN
tables produced by PCAL are compared.
PCAL SU tab The U flux for IF=2 determined by PCAL in the SU table
CLCOR CL 1 tab The real part of IF 1, RCP of the CL table produced by
CLCOR is compared. Every 25th element of the table is
CLCOR CL 2 tab The imag part of IF 2, LCP of the CL table produced by
CLCOR is compared. Every 25th element of the table is
SPLIT uv The output of SPLIT is compared.
IMAGR ICL001 map The I images from IMAGR are compared.
IMAGR IBM001 map The I beams from IMAGR are compared.
IMAGR QCL001 map The Q images from IMAGR are compared.
Task LISTR is used to apply polarization calibration to the polarization
angle calibrator to verify the correctness of the calibration. The
LISTR output should look something like the following:
MVLAC .UVDATA. 1 Vol= 5 User= 1 Channel=1 IF=2
Freq= 8.711000000 GHz Ncor= 4 No. vis= 2705
Stokes = FULL Subarray = 1
Applying calibration table 3
Applying polarization corrections
Applying flag table 1
Time = 1/18:13:20 to 1/18:17:20 Source = 3C286 :0000
Flux = 5.1045 Jy, Calcode = B , Freq = 8.711000000 GHz
Phases in degrees, averaging type = Vector
RL in upper right, conjg(LR) in lower left
Ant -- 3----13---- 5---- 9----21---- 4----23----20----24--
3| 73 70 68 70 69 68
13| 65 72 68 67
5| 61 69 67
9| 62 68 65
21| 62 66 64 63
4| 63 64 64 67 65 66
20| 60 66 66 66
24| 63 69 66 68 64 66
Matrix average = 6.60303E+01 sigma = 4.81587E-01