; VBMRG ;--------------------------------------------------------------- ;! Merge VLBI data, eliminate duplicate correlations ;# TASK VLBI ;----------------------------------------------------------------------- ;; Copyright (C) 1995, 2006 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- VBMRG LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC VBMRG Task to merge 'BT' sorted VLBI data. INNAME Input UV file name (name) INCLASS Input UV file name (class) INSEQ 0.0 9999.0 Input UV file name (seq. #) INDISK 0.0 9.0 Input UV file disk unit # OUTNAME Output UV file name (name) OUTCLASS Output UV file name (class) OUTSEQ -1.0 9999.0 Output UV file name (seq. #) OUTDISK 0.0 9.0 Output UV file disk unit #. YINC 0.0 99999. Integ. time of data (sec) ---------------------------------------------------------------- VBMRG Task: This task will consolidate a 'BT' sorted VLBI uv dataset. The last visibility with the heighest weight for each correlator will be passed. The purpose of this task is to remove redundant processings of data. This task will read (and then write) compressed data. However, the results will be different from those obtained with uncompressed data. Compressed data assigns a single weight to all IFs and spectral channels equal to the highest weight found in any of them. If different IFs have different weights, then the uncompressed data sets will allow different processings to be selected for different IFs. Compressed data will select the same processing for all IFs. 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 file. 0 => any. Input UV sort must be 'BT'. 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 file. 0 => highest w room YINC.......The integration time of the data. Times within a window of this width will be considered identical. Value is in sec. Default = minimum = 0.2 sec. ---------------------------------------------------------------- VBMRG: Task to eliminate duplicate correlations of VLBI data. DOCUMENTOR: Jim Ulvestad NRAO/CV RELATED PROGRAMS: UVSRT, MSORT PURPOSE VBMRG consolidates a VLBI data base which has been sorted in baseline-time ('BT') order. The task is necessary because the multiple processings on a 10+ station processor that are required in a many-antenna experiment will cause some baselines to be correlated more than once. VBMRG searches the old data base picking out only one record for each baseline at each time; it writes a new data base specified by OUTNAME. This new data base will contain only a single record for each baseline within the time window specified by YINC. VBMRG cannot be run on processed data sorted in time-baseline ('TB') order. That data must first be run through UVSRT with the sorted order 'BT' specified. See comments below. COMMENTS INNAME: The input file must be sorted in 'BT' order. OUTDISK: Although VBMRG will create a new data set that is somewhat smaller than the old set, the user must be sure there will be enough space on the OUTDISK to accommodate the new data base. Running several UVSRTs and VBMRG on a large data set will quickly eat up the available disk space, so old versions of the data base should be deleted as soon as they're no longer needed. OUTDISK = 0 will cause the task to try all disks. YINC: The default value of this parameter should be used in most cases. If YINC is specified, it must not be set to be longer than the integration time for a single record, which will result in the discarding of good, unduplicated visibility records. INTERACTION WITH OTHER PROGRAMS: As mentioned above, VBMRG can be run only on data sorted in 'BT' order. Before VBMRG can be run, UVSRT must be run to sort the data into this order. Then VBMRG will run through a single baseline at a time, selecting only a single visibility record from each time. The selected record will be the one given the highest weight (or last-written, for equal weights). The output file specified by OUTNAME will contain only unduplicated data from a single correlation of each baseline. Before the global fringe-fitting task (FRING) can be performed, the data base must be re-sorted by use of UVSRT with sort order 'TB' (time-baseline). Thus UVSRT must be run twice, once before and once after VBMRG. DISK SPACE: The disk space used by the output file will be initially the same space as used by the input file. Depending on the fraction of redundant correlations performed in the processor, the final file will be somewhat smaller. For example, optimum processing of a 5-station experiment will require 4 passes on a 3-station processor, giving 10 unique correlations and 2 redundant ones. In this case, the output of VBMRG should occupy about 16% less disk space than the input file. RECIPE FOR USE: -- Use FITLD to load data from multiple station-subset correlation passes, with concatenation ON. Output datasets can be either compressed or uncompressed. NOTE: This data MUST be the raw correlator jobs, not the semi-processed files from the archive. -- Use UVSRT to sort into BT order. -- Use VBMRG to select unique records. -- Use UVSRT to re-sort into TB order (for most purposes). -- Run INDXR to re-index the final dataset.