AIPS HELP file for UVSRT in 31DEC24
As of Sat Apr 27 21:23:47 2024
UVSRT: Task which sorts UV data
INPUTS
INNAME Input UV file name (name)
INCLASS Input UV file name (class)
INSEQ 0.0 9999.0 Input UV file name (seq. #)
INDISK Disk unit # of input UV data
OUTNAME Sorted UV file name (name)
OUTCLASS Sorted UV file name (class)
OUTSEQ -1.0 9999.0 Sorted UV file name (seq. #)
OUTDISK Disk unit # of sorted UV data
0 => highest with space
If outfile spec. equals the
infile spec., output will
overwrite the input
BADDISK Disk drive #'s to avoid
SORT Two char. sort order, eg.'XY'
blank => 'XY'
ROTATE -360.0 360.0 Angle thru which to rotate.
positive rotates CCW
DEFER -1.0 1.0 Defer output file creation?
HELP SECTION
UVSRT
Type: Task
Use: To sort UV data into a specified order. The data are
sorted into ascending values of the two keys (two are
always used in the sort).
NOTE: this task does NOT apply flagging or calibration tables
to the input UV data. Run SPLIT first if that operation is
desired.
Adverbs:
INNAME.....Input UV file name (name). Standard defaults.
INCLASS....Input UV file name (class). Standard defaults.
INSEQ......Input UV file name (seq. #). 0 => highest.
INDISK.....Disk drive # of input UV. 0 => any.
OUTNAME....Output UV file name (name). Standard defaults.
OUTCLASS...Output UV file name (class). Standard defaults.
OUTSEQ.....Output UV file name (seq. #).0 = > highest unique.
OUTDISK....Disk drive # of output UV. 0 => highest with space
If the outfile specification equals the infile
specification, the output data file will overwrite the
input data file. See DEFER below.
BADDISK....Disk drive #'s of bad disks (for scratch files).
SORT.......Sort order of output. blank => 'XY' and is the sort
order needed for input to UVMAP.
see HELP SORT for more information
ROTATE.....Angle thru which to rotate map, positive is CCW.
(degrees) rotation of the image.
DEFER......True (> 0) means to defer the creation of the output file
until the sort is complete and one of the 2 scratch files
has been deleted. This allows a smaller the task to
require disk space "only" two times that of the input
file rather than three times required if the output does
not overwrite the input.
EXPLAIN SECTION
UVSRT: Task which sorts UV data
DOCUMENTOR: E.B.Fomalont (NRAO/VLA)
RELATED PROGRAMS: UVLOD, UVMAP, CALIB, IMAGR, MSORT, OOSRT
PURPOSE
UVSRT will sort a UV data base into a specified order. The
program is generally used after UVLOD and before UVMAP in order
to sort the data from time-baseline order 'TB' into order of
descending abs(u) spacing, which is designated as 'XY', needed
for UVMAP. Before using CALIB to self-calibrate a data base
the UV sort order must be 'TB'. IMAGR can also image data in 'TB'
order. The order of the data base can be found by using the verb
IMHEADER. After concatenation of data bases, UVSRT must be run to put
the data into 'TB' or 'XY' order.
This task does not use the array-processor but it is a very
heavy user of the cpu power and disk space. If a data base of
length N is sorted, it requires three areas of length N. Two
areas are needed as scratch files and one is needed for the
output data base. The latter can be avoided by overwriting the
output onto the input.
COMMENTS
OUTNAME, OUTCLASS, OUTSEQ, OUTDISK:
If the outfile specification is identical to the infile
specification (including defaults used in both file
specifications), then the sorted data will overwrite the input
data. Make sure the input data set is properly backed up before
you overwrite since a computer crash may destroy the input data
set.
SORT:
The sort order is specified by two keys which are
characters in the adverb SORT. The legal keys are:
blank => X = descending ABS(u)
B => baseline number
T => time order
U => u spatial freq. coordinate
V => v spatial freq. coordinate
W => w spatial freq. coordinate
R => baseline length.
P => baseline position angle.
X => descending ABS(u)
Y => descending ABS(v)
Z => ascending ABS(u)
M => ascending ABS(v)
ROTATE:
A positive number will rotate an image counter-clock-wise.
That is, an image made from the sorted data with ROTATE=30 will
produce an image which is rotated 30 degrees counter-clock-wise
when compared with the image made from the sorted data with
ROTATE=0.
Map rotation is useful for orienting long, thin sources
vertically or horizontally in order to permit smaller,
rectangular maps to be made. This rotation cannot be done in
UVMAP since it reorders the UV data. It is usually more
convenient to orient the source with its long axis vertically
rather than horizontally when using subsequent display software.
DISKSPACE, BADDISK:
UVSRT is clever enough to know if the amount of disk space
is sufficient at the start of execution and this space is
allocated immediately. If disk space is insufficient, writing
the output data over the input data may help (as long as the
input data set is backed-up properly). The working scratch file
and the output data file need not be on the same disk. When
other people are using a private disk pack, it is best to not
use this pack for the scratch file since the private disk pack
may be dismounted during your execution. Use BADDISK=N where N
is the disk drive number to avoid this problem.
TIMING:
The program run time on an otherwise empty VAX 11-780 is
50 * (D/500,000) **1.1 minutes
where D is the number of visibility points. All of the four
Stokes parameters are sorted together.