; TD_STEP3 ;--------------------------------------------------------------- ;! Time-dependent imaging procedure "step 3" ;# procedure AP IMAGING OOP INTERACTIVE ;----------------------------------------------------------------------- ;; Copyright (C) 2014 ;; 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 ;----------------------------------------------------------------------- TD_STEP3 LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC TD_STEP3 Third step in time-dependent imaging INNAME Input UV data (name) INCLASS Input UV data (class) INSEQ Input UV data (seq. #) INDISK Input UV data disk drive # TD_TIMES List of time limits for the "short" time intervals (days) PRTLEV Debug level displays: 1 INPUTS for each task 2 IMHEAD for each task OUTNAME Output image name (name) OUTDISK Output image disk drive # ******** IMAGR parameters ************** NCHAV Number of chan. to average. CHINC Channel incr. between maps. CELLSIZE 1.E-12 (X,Y) size of grid in asec IMSIZE 0.0 8192. Minimum image size NFIELD 0. 4096. Number of fields (max 4096) DO3DIMAG -1.0 1. > 0 => use different tangent points for each field FLDSIZE -1. 8192. Clean size of each field. RASHIFT RA shift per field (asec) DECSHIFT DEC shift per field (asec) UVTAPER 0. (U,V) Gaussian taper units are kilo-lambda UVRANGE 0. Min & max baseline (klambda) GUARD -1.0 0.9 x,y guard band fractional radius ROTATE Rotate image CCW from N by ROTATE degrees ZEROSP 0-spacing fluxes and weights SEE HELP!! UVWTFN UV dist. weight function UVSIZE 0. Array size for doing uniform weights. 0 -> actual field size. ROBUST Robustness power: -5 -> pure uniform weights, 5 => natural UVBOX 0. 128. Additional rows and columns used in weighting. UVBXFN Box function type when UVBOX > 0. 0 -> 1 round pill box. XTYPE 0. 10. Conv. function type in x default spheroidal YTYPE 0. 10. Conv. function type in y default spheroidal XPARM Conv. function parms for x YPARM Conv. function parms for y NITER * 0.0 Maximum # of Clean components BOXFILE Input file of field params and Clean boxes; ' ' => use FLDSIZE, RASHIFT, DECSHIFT, NBOXES, CLBOX only. OBOXFILE * Output file for final Clean boxes GAIN * 0.0 2.0 Clean loop gain FLUX * Minimum Clean component (Jy) MINPATCH * 0.0 Min. BEAM half-width in AP. BMAJ * -999.9 FWHM(asec) major axis Clean * restoring beam. BMIN * -999.9 FWHM(asec) minor axis Clean * restoring beam. BPA * -360.0 360.0 Clean beam position angle OVERLAP -1.0 1 => restore components to overlapped fields, >=2=> expect overlaps in Cleaning ONEBEAM -1.0 1.0 > 0 use only 1 dirty beam per scale in multi-facet Cleans OVRSWTCH -0.9 0.9 Not 0 => switch from OVERLAP >= 2 to OVERLAP 1 - see HELP FACTOR * -5.0 5.0 Speedup factor see HELP CMETHOD * Modeling method: * 'DFT','GRID',' ' IMAGRPRM Task enrichment parameters (1) Antenna diameter (m) (2) Source Spectral index (3) Frequency scaling factor (4) > 0 -> SDI Clean factor (5) >0 => scale residuals (6) Half-width in x of box (7) Half-width in y of box (8) Filter components whose neighborhood is weaker than IMAGRPRM(8) Jy. 0 -> don't (9) Radius in pixels for the IMAGRPRM(8) test. (10) multiplier of image size to get beam size: 0 => 2; 2, 1, 0.5 0.25 supported (11-16) Multi-scale controls (17) spectral index radius 0 -> no correction (18) Limit grids (see help) (19) Dynamic range limit (20) Retry factor (see help) IMAGRPRM ? Task enrichment parameters ? (1) Antenna diameter (m) ? (4) > 0 -> SDI Clean factor ? (5) >0 => scale residuals ? (6) Half-width in x of box ? (7) Half-width in y of box ? (8) Filter components whose ? neighborhood is weaker than ? IMAGRPRM(8) Jy. Can TELL ? only if non-zero on GO. ? 0 -> no filtering. ? (9) Radius in pixels for the ? IMAGRPRM(8) test. ? (11-15) Multi-scale controls ? (18) Limit grids (see help) ? (19) Dynamic range limit ? (20) Retry factor (see help) IM2PARM Yet more parameters: (1) Auto boxes: allowed # (2) : island level (3) : peak required (4) : limit wrt max (5) : extend boxes (6) : edge skip (7) reset boxes for next chan (8) TV timeout interval: init (9) timeout after 1st: in sec (11) baseline-dependent avg max time in sec (12) field size 0 -> infinite (13) Number channels averaged IM2PARM ? Yet more parameters: ? (1) Auto boxes: allowed # ? (2) : island level ? (3) : peak required ? (4) : limit wrt max ? (5) : extend boxes ? (6) : edge skip ? (9) timeout after 1st: in sec NGAUSS 0.0 10.0 Number of scales to use WGAUSS 0.0 Scales in arc sec >= 0 FGAUSS 0.0 Minimum flux for each resol. MAXPIXEL * 0.0 500000.0 Maximum pixels searched in * each major cycle. IN3NAME Spectral index image name IN3CLASS Spectral index image class IN3SEQ Spectral index image sequence number IN3DISK Spectral index image disk IN4NAME Spectral curvature name IN4CLASS Spectral curvature class IN4SEQ Spectral curvature sequence number IN4DISK Spectral curvature disk FQTOL Frequency tolerance in kHz (primary beam & spec index) DOTV * -1.0 4096.0 Display residuals on TV ? Start with field = DOTV BADDISK -1.0 1000.0 Disks to avoid for scratch. ---------------------------------------------------------------- TDSTEP3 Type: Procedure Use: See HELP TDEPEND for a full discussion. TDSTEP3 taks as input a fully calibrated and edited single source file. It then loops over time intervals doing: a. SPLIT to make 'ISPLIT' containing all data for time range(i) b. IMAGR of NFIELDS+1 where NFIELDS is the number of facets required to image the full area and facet NFIELDS+1 is centered on the time-variable target source. BOXFILE must include all NFIELDS+1 facets and should do an UNClean box on the target source wherever it occurs in facets numbered <= NFIELDS and should do UNClean boxes surrounding the source in facet NFIELDS+1. The latter is really only required if you do auto-boxing. Note that you will be doing deeper imaging at a later stage. c. UVSUB subtracts facet NFIELDS+1 from ISPLIT and appends the data in a file with class 'APPEND' d. It then deletes ISPLIT and all images and beams. The output of this step is a UV data set from which the time-variable target source has been removed (as best one can at this early point). It has name OUTNAME, class 'APPEND', sequence 1, and disk OUTDISK. Adverbs: INNAME.....Input UV data file (name). Standard defaults. INCLASS....Input UV data file (class). Standard defaults. INSEQ......Input UV data file (seq. #). 0 => highest. INDISK.....Input UV data file disk drive #. 0 => any. SOURCES....Source name - specify at most 1. TD_TIMES...A list of break times for imaging intervals in which the target source is not likely to change. Time interval I is TD_TIMES(I) to TD_TIMES(I+1) in days. PRTLEV.....For debug purposes: 1 => INPUTS for each task are printed. 2 => IMHEADER for each input file is also printed. 3 => also INPUTS for each zap, 4 also IMHEADER for each zap. OUTNAME....Output image name (name). Standard defaults. Used for data set called class APPEND only. OUTDISK....The disk drive # of almost everything. 0 => highest with space but you shoukd not depend on this. ************ Adverbs strictly for IMAGR ************************ NCHAV......NCHAV is the number of channels to be averaged together in in the gridding process. 0 => 1. If this value is less than the total number of channels, then a multi-channel image will result. Note that the last output channel may include data from fewer than NCHAV input channels unless ECHAN, BCHAN, CHINC, and NCHAV are very carefully chosen. The term "averaged" applies to the output image; each channel is kept separate in the uv data used in the imaging so that it may be gridded and model subtracted at the correct frequency. IM2PARM(13) overrides this and actually averages a number of channels together on the fly before gridding. Be aware that the values of NCHAV, CHINC, and IM2PARM(13) interact and should be consistent. CHINC......Number of input channels to skip between images. 0 => 1 The i'th output channel includes input channels BCHAN + (i-1)*CHINC through MIN (ECHAN, BCHAN + (i-1)*CHINC + NCHAV - 1). See also IM2PARM(13) for considerations. CELLSIZE...(X,Y) pixel separation in asec. IMSIZE.....(X,Y) The minimum desired size of the fields regardless of the FLDSIZE for component search. NFIELD.....The number of fields to map in the antenna beam. Up to 4096 are allowed. Note that only 64 fields may be described in adverbs, but 4096 are allowed. If you want to set Clean boxes in advance for more than the first field, or wish to specify RASHIFT, DECSHIFT, FLDSIZE, or BCOMP for fields > 64, you must use the BOXFILE option. If the multi-scale option is used, the actual number of fields imaged will be NFIELD*(Number of scales) and that product is limited to 4096. TDSTEP3 SPECIAL USAGE: facet NFIELD+1 containing the target source must also be specified and will be imaged. Mark the target with an UNClean box in the facet(s) which would normally contain it. In facet NFIELD+1, Clean only the target source - if auto-boxing you will have to put UNClean boxes around the target to keep those areas from being Cleaned in the special facet and, of course, put a Clean box on the target in the special facet. See BOXFILE for info on UNClean boxes. DO3DIMAG...> 0 => make the images by shifting the tangent point to the field center. This is more accurate for significant shifts than simply moving the w term to the field center which is what happens with DO3DIM <= 0. It turns out that this option costs only about 1% of the cpu time when it is not needed and may make Cleans go very much faster when it is needed. Beginning April 2009, DO3D false will do a more accurate implementation called by some "faceting in the uv plane". That mode should be reasonably accurate and the resultings should FLATN more easily. FLDSIZE....(X,Y) field size in pixels for the component search during Cleaning; one per field. Should be in the range 32X32 to 8192X8192. Output image size will be increased to the next highest power of two (or IMSIZE if that is greater), but only the region specified will be searched for components. Default is IMSIZE-10. Set FLDSIZE(1,i) and FLDSIZE(2,i) = -1, if you want there to be NO clean box initially in field i. This isn't necessary if you are using auto-boxing (IM2PARM(1) > 0). TV options may be used to delete, change and create Clean boxes interactively. The BOXFILE option and the NVSS WWW server may help in entering these values;see below. RASHIFT....RA shift of the phase center of each field from the tangent point of the uv data in asec. Map center = tangent point + shift. If X>0 shifts map center to east. NOTE: RASHIFT is a shift in RA scaled by cos (Dec_0) as Ra_new(i) = RA_0 + RASHIFT(i) / cos (Dec_0) where _0 => the tangent point in the uv data. This is a change for 15OCT99 from shifts in -SIN projection (which do not work for -NCP data and large angles). If the UV data have been rotated then RASHIFT and DECSHIFT refer to X and Y in the new coordinate system. The BOXFILE option and the NVSS WWW server may help in entering these values;see below. DECSHIFT...Declination shift of map center from tangent point of each field in asec. Map center = tangent point + shift. If Y>0 shifts map center to north. The BOXFILE option and the NVSS WWW server may help in entering these values;see below. UVTAPER....(U,V) Gaussian taper (kilo-lambda) at 30% level UVRANGE....(Minimum,Maximum) baseline (kilo-lambda) in map. GUARD......Fraction of the x and y radius for which uv samples are not allowed. < 0 => just enough to avoid mathematical errors in the convolution. 0 => 0.3 * SQRT(taper weight at 0.3 from edge). ROTATE.....Rotation angle to be applied in degrees. ZEROSP.....(1)= zero spacing Stokes I flux density. Zero spacing flux is placed at the center of FIELD 1. (2)= zero spacing Stokes Q flux density (3)= zero spacing Stokes U flux density (4)= zero spacing Stokes V flux density (5)= weight for zero spacing flux. Both ZEROSP(1) and ZEROSP(5) must be > 0 to apply this option. The zero-spacing data sample is appended to the end of the input data set and participates in any uniform weighting, gridding, etc. in the same way any other sample does. ******* NOTE THAT THIS IS NOT THE SAME AS OTHER IMAGING TASKS USAGE OF ZEROSP. **************** UVWTFN.....Weighting function of (u-v) plane in 2 character code. If the 1st character is N use "natural" weighting (the weights attached to the data with no variation due to local density). Otherwise, use "uniform" weighting in which the weights are scaled by the local density of weights under control of adverbs UVSIZE, UVBOX, UVBXFN, and ROBUST. The second character (and also the first) controls any alteration of the weights to be done before they are used in the natural or uniform weighting: 2nd character = S => take square root of weight_in 2nd character = V => take fourth root of weight_in 2nd character = O => use 1.0 UVWTFN = 'CS' => take 1 / square root of weight_in UVWTFN = 'CV' => take 1 / fourth root of weight_in UVWTFN = 'C?' => take 1 / weight_in where ? is any character except S, V, O UVSIZE.....Size of the array used to count samples for uniform weighting. Does not have to be a power of two and can be smaller than or bigger than the image size. The default is the size of the first output image. ROBUST.....Briggs' "robustness" parameter. "Uniform" weights are tempered by a constant being added to the local density of weights. ROBUST = -4 is nearly pure uniform weighting, ROBUST = +4 is nearly pure natural weighting. Use of this option requires a second array in the "AP" memory and may therefore force the data to be sorted. The option is turned off if ROBUST < -7 and uniform weighting is turned off is ROBUST > 7. See HELP ROBUST - the AIPS ROBUST differs numerically from that of Briggs. UVBOX......(U,V) box size for weighting. This is the support radius over which a sample is counted. I.e., the sample or its weight is counted over an area 2*UVBOX+1 cells on each side in the UV plane, where the UV cell size is (after correcting units) given by 1 / (UVSIZE(i) * CELLSIZE(i)). UVBXFN.....If UVBOX > 0, UVBXFN controls how the samples are counted as a function of u and v (UVBXFN < 0) or of radius (UVBXFN > 0). In the latter case, the function is 0 for radius > UVBOX. Functions are pill box, linear, exponential, and Gaussian for ABS(UVBXFN) = 1-4, resp. 0 -> 1. See HELP UVBXFN. XTYPE......Convolution function type in X-direction 1=Pill-box, 2=exponential, 3=Sinc, 4=Exp*Sinc, 5=Spheroidal, 6=exp*BESSJ1(x)/x. <= 0 or > 5 -> 5. YTYPE......Convolution function type in Y-direction XPARM......Array containing parameters for XTYPE. See HELP UVnTYPE when n=convolution type. YPARM......Array containing parameters for YTYPE. NITER......Clean iteration limit. 0 => no Cleaning. BOXFILE....Input text file used to simplify the specification of large numbers of fields and/or large numbers of Clean boxes. Leading and trailing blanks from all lines in the text file are discarded, so "column 1" below means the first non-blank column in the card. This option is used to specify field parameters for fields 1 through NFIELD which are then copied to the fields used for additional scales (if any). To specify a field's parameters, put the letter F or f in column 1 followed by the field number, the X and Y FLDSIZE values, the RASHIFT amd the DECSHIFT for the field (separated by blanks). Any field specified in this way overrides the corresponding parameters given in the adverbs. Thus, F 2 450 450 -25.5 6.7 specifies that field 2 is to have a FLDSIZE of 450x450 with an RASHIFT of -25.6 and a DECSHIFT of 6.7 arcsec. If this is the only F card in the file, then fields 1 and 3 through NFIELD are set by the adverb values. As an alternative, a field may also be specified with a "coordinates" card having a C or c in column one. After the C, give the field number, the X and Y FLDSIZE values and the center Right Ascension (HH MM SS.S) and Declination (signDD MM SS.S) separated by blanks. Thus C 2 450 450 11 34 45.67 -00 14 23.1 specifies that field 2 is to have a FLDSIZE of 450x450 with a center RA of 173.6902917 degrees and a center Declination of -0.23975 degrees. All 9 numbers must be given; the sign is optional for positive declinations and is given only on the degrees term. To set a BCOMP include put the letter B or b in column 1 followed by the field number and the value of BCOMP to be used. Thus, to include no components from field 98 and some from 99 include the lines: B 98 0 B 99 243 Fields 1 through NFIELD*(Number of scales) may be specified. To set Clean boxes, specify one box per line, as field blc-x blc-y trc-x trc-y (5 integers) e.g. 1 200 205 220 222 1 230 232 240 241 2 100 100 130 121 ... or circular "boxes" as field -1 radius center-x center-y (5 ints) e.g. 001 -1 10 210 214 001 -1 5 235 237 .... Column 1 must contain a numeric character (part of the field number); otherwise the line is treated as some other sort of line. Fields with no boxes specified -- and auto-boxing turned off (IM2PARM(1) = 0) --- default to the size specified by IMSIZE and FLDSIZE (see above and including FLDSIZEs read from this file). This option overrides NBOXES and CLBOX if any boxes for field one appear in the file. Otherwise, those adverbs are used for field 1. E.g. BOXFILE 'FITS:BOXES' Fields 1 through NFIELD*(Number of scales) may be specified. If you do not give boxes for a field > NFIELD, then the boxes for the corresponding field at full resolution (0 scale) are copied to those at the lower resolutions (larger scales). If BOXFILE = ' ', NBOXES and CLBOX apply unchanged as do the FLDSIZE, RASHIFT, and DECSHIFT adverbs. The NVSS WWW server may help in preparing these values;see below. The number of Clean boxes per field is limited to min [ 4096, (64*4096)/(NFIELD*NGAUSS) ] To specify that a field has no Clean boxes, specify the BLC and TRC as four zeros. To mark regions which should never be Cleaned, include lines beginning with U or u. Following that character with at least one blank, enter the facet number and four values as for Clean boxes (i.e either rectangular or circular). The UNClean boxes may be changed with the TV when DOTV is true. Thus, for example U 2 100 100 130 121 u 001 -1 5 235 237 will protect one area in each of facets 1 and 2 from Cleaning. This option is primarily used to isolate a source to one special facet and to keep it from being Cleaned in another facet. Modeling routines may then use the special facet - or all facets except the special one - to isolate the source. Task CCEDT is also used for this purpose when UNClean boxes have not been used. When combining more than one spectral channel or IF, you may wish to alter their relative weights in a temporary fashion. The BOXFILE option allows this with W cards: W in column 1, then a weight, then a channel number (0 -> all), and last an optional IF number (absent -> 0, 0 -> all). For example: W 0.1 1 W 0.5 2 W 0.8 2 3 W 0.1 63 Assigns weight 1 to all channels 3-62, weight 0.1 to all channels 1 and 63, weight 0.5 to channel 2 except for 0.8 in channel 2, IF 3. These "weights" multiply the weights already assigned to the data. When imaging with multiple facets, especially with multiple scales, you may wish to have some of the facets ignored in the Cleaning. To do this, give "I" cards with a facet number or a range of facet numbers as I 18 I 23 36 to image facets 18 and 23 through 26 but never consider them for Cleaning. Note, when giving a range, the first number must be lower than the second number. The BOXFILE option is essential when NFIELD > 64. OBOXFILE...Output text file to record the Clean boxes used. If BOXFILE is also used and OBOXFILE points at a new file, then IMAGR starts by copying all of BOXFILE to OBOXFILE. Then, each time a TV REBOX or TVBOX is selected the file is rewritten (as the TV interaction ends) with all of the Clean boxes currently in force for all fields. The lines in the file containing other kinds of information are retained throughout. Thus, one can set OBOXFILE=BOXFILE or for safety make a new OBOXFILE but then use that as input the next time. GAIN.......The Clean loop gain. 0 => 0.10. FLUX.......Stop Clean when abs(resid. image max) < FLUX in Jy. If FLUX < 0 then Clean stops after the first negative Clean component (the actual value of FLUX is then irrelevant). Note that on restarts and in OVERLAP < 2 mode, when the residual levels are known for all fields, the Clean is stopped if all fields are below 1.05 * FLUX. When each facet is Cleaned, the Clean proceeds until the next component is less than 1.0 * FLUX however. This "slop" is to prevent expensive major cycles being initiated to deal with weak bumps that appear after the model has been subtracted and the fields re-imaged. MINPATCH...Minimum half width of the portion of the beam which is used in the AP minor Clean. (init 51) Use 51 for deep Cleans of extended sources. Use a large value if the beam has big side-lobes. BMAJ.......The FWHM (asec) major axis of the restoring beam. If 0; value obtained from fitting to the beam. If <0; output will contain the residual image. This is for the point-source resolution. It will be corrected to the other scales (if any). BMIN.......The FWHM (asec) minor axis of the restoring beam. BPA........The position angle in the unrotated image of BMAJ. OVERLAP....If <= 0, components found in one field are restored only to that field even if they occur at a coordinate found in one or more other fields. If >0, components from each field are restored to all fields that they overlap. For OVERLAP<2, all fields are Cleaned in each major cycle. For OVERLAP >= 2, one field is Cleaned and its components subtracted from the uv data before the next field is imaged and Cleaned. This prevents the slow convergence which happens when Clean boxes in two fields actually cover the same emission. It also reduces the affects of sidelobe bumps of strong sources appearing to be sources in the weaker fields. If OVERLAP>0, the output CC files will have been merged. If OVERLAP>=2, you can control which field is Cleaned next, but only if the task runs interactively (set DOWAIT=TRUE before GO IMAGR). OVERLAP >= 2 must be used if you use the multi-scale option below. OVERLAP>=2 is believed to be a superior Clean method, but it may be slower than OVERLAP=1. See a suggestion below. Set OVERLAP = N (where N > 2) to force all images to be recomputed with filtering every N Cleans. You may also force recomputing from the TV menu. ONEBEAM....> 0 => do only one beam pattern per scale for either value of DO3DIMAG. Note that the facet beams are different, but it has been argued that they are not enough different to matter with uv-plane based Cleans. OVRSWTCH...Parameter to allow switching between OVERLAP >= 2 mode and OVERLAP = 1 mode when the peak residual is less than abs(OVRSWTCH) * Initial_Peak where Initial_Peak is the peak found at the beginning of the Clean. If OVRSWTCH > 0, ONEBEAM is not changed in the switch. If OVRSWTCH < 0, ONEBEAM is made true in the switch. This implements the suggestion below but avoids the tricky parts of a restart. Note that switching is not allowed for multi-scale imaging (NGAUSS > 1). In OVERLAP 1 mode the Clean boxes are examined for overlap between facets frequently and the smaller of the overlapped boxes is removed from the list. ------------------------ SUGGESTION: Use OVERLAP=2 and ONEBEAM=FALSE at the start of major multi-facet Cleans and run them until the high dynamic range signals have been Cleaned. Then restart with those Clean components using OVERLAP=1 and ONEBEAM=TRUE for the weaker components in a more efficient Clean. NOTE that you must be careful to Clean each source region in only one facet if you use OVERLAP=1 mode. Multi-scale Clean is not available in OVERLAP < 2. ------------------------ FACTOR.....FACTOR>0 causes deeper Clean in each major cycle, speeding Clean, maybe "eating" extended structure. OVERLAP=2 mode may need speeding with FACTOR and/or larger MAXPIXEL. FACTOR=0 => the normal Clark Clean. FACTOR=-0.3 is good for deep Cleans of extended structure. CMETHOD....This determines the method used to compute the model visibility values. 'DFT' uses the direct Fourier transform, this method is the most accurate. 'GRID' does a gridded-FFT interpolation model computation. ' ' allows the program to use the fastest method, except that DFT will be used on images <= 128 for accuracy reasons. IMAGRPRM...Correction control parameters (SEE EXPLAIN IMAGR): (1) If > 0 then make frequency dependent primary beam corrections assuming an antenna diameter of IMAGRPRM(1) meters. Can change with TELL which only makes sense if you are going to repeat the subtraction with a filtered set of components (see IMAGRPRM(8)). Note that VLA and ATCA arrays (TELESCOPE header parameter) use the default primary beam parameters defined elsewhere in AIPS, while other antennas actually use IMAGRPRM(1) as the diameter of a "standard" telescope. See FQTOL below also. (2) Visibility amplitudes will be corrected to the average frequency assuming a spectral index of IMAGRPRM(2). Note: the typical optically thin synchrotron spectral index is about -0.7. (3) If > 0, then the u,v and w terms are scaled by IMAGRPRM(3) before imaging. (4) If > 0, then SDI Clean will be used when the fraction of residual pixels in the Clean boxes stronger than half the maximum residual exceeds IMAGRPRM(4). <= 0 -> never use or allow SDI Clean. Can change with TELL. If SDI Clean is enabled, the output CC files will have been merged. (5) If > 0 then scaling of residuals is requested and (6) Half-width in x of box to determine the dirty beam area (default = 5) (7) Half-width in y of box to determine the dirty beam area (default = 5) Can change (5)-(7) with TELL. (8) If non-zero, select only those Clean components having > ABS(IMAGRPRM(8)) Jy within a radius of IMAGRPRM(9) cells of the component. If IMAGRPRM(8) < 0, the abs value of the flux near the component is used. This is an optional filter to remove weak isolated components which can cause a significant bias. Can change with TELL but only if it was non-zero to begin with. A copy of the input data has to be made for this option and it is only made if IMAGRPRM(8) is non-zero. If this option is selected, the output CC files will have been merged. Note that IMAGRPRM(8) should always be <= 0 for images of Q, U, and V Stokes parameters since negative brightnesses are valid. Filtering is done on restarts, when requested from the TV, on certain Cleaning failures, on normal completion (after which the task may resume Cleaning depending on IMAGRPRM(9) until the completion points such as NITER and FLUX are reached a second time) and on final exit. If ALLOKAY >= 2, the filter is not applied on the restart. If the filtering option was selected at the start (IMAGRPRM(8) non zero), it may be turned off by setting IMAGRPRM(8) exactly 0 and running TELL. To delete all negative regions, set IMAGRPRM(8) to a tiny positive number. (9) The abs(IMAGRPRM(9)) is the radius in cells for the area in which fluxes are computed. If IMAGRPRM(9) < 0, the Clean will restart following the "final" filtering on the assumption that enough changes are made by the filter that more Cleaning will be needed. abs (IMAGRPRM(9)) < 1.1 => 3.1. Can change with TELL. (10) = multiplier of max image size to set beam size. Values of 2, 1, 0.5, and 0.25 are allowed. 0 => 2. Smaller beam images are a bit faster, but less accurate in the early Clean cycles. The largest beam image used is 2048 on a side except when IMAGRPRM(1) > 0.75. When IMAGRPRM(10) is 1, the limit is 4096 and when IMAGRPRM(10) > 1.5, the beam is twice the image size limited by 32768. Multi-scale experimental controls are based on BeamRatio = (field beam area) / (min beam area) (11) Multi-scale experimental control: select which field to Clean using peak fluxes (in Jy/beam) weighted by 1 / (BeamRatio)**IMAGRPRM(11). This is important. (12) Multi-scale experimental control: decrement the value of IMAGRPRM(11) used above by IMAGRPRM(12) each time an non-point resolution field is Cleaned until it is 0. (13) Multi-scale experimental control: use gain = GAIN * [ {1/BeamRatio} ** IMAGRPRM(13) ] (14,15) Multi-scale experimental control: use factor = FACTOR * (1 - IMAGRPRM(14) * [ 1 - 1.0/({BeamRatio} ** IMAGRPRM(15)) ] (16) Multi-scale experimental control: use maxpixel = MAXPIXEL + IMAGRPRM(16) * (BeamRatio) Multi-scale experimental control limits: 0 <= IMAGRPRM(11) <= 1.0 not changed by TELL 0 <= IMAGRPRM(12) <= 0.1 changed by TELL 0 <= IMAGRPRM(13) <= 1.0 changed by TELL 0 <= IMAGRPRM(14) <= 1.0 changed by TELL 0 <= IMAGRPRM(15) <= 1.0 changed by TELL 0 <= IMAGRPRM(16) changed by TELL (17) 1 => use a spectral-index image represented in IN3NAME, IN3CLASS, IN3SEQ, IN3DISK below to correct the Clean component model for each channel. IN4NAME et al will also be used as a curvature image iff IN3NAME are specified. IMAGRPRM(17)-0.5 is used as a radius in pixels over which the spectral index image is averaged. When it is small (0 < IMAGRPRM(17) <~ 1), the spectral index is interpolated rather than averaged. See FQTOL below as well. When doing spectral index, the primary beam correction (IMAGRPRM(1)) costs very little extra. (18) In OVERLAP>=2 mode, when imaging multiple fields, IMAGR grids and FFTs multiple fields in an attempt to determine the next one to Clean. Multiple fields are done to reduce I/O in this search which may otherwise have to re-read the work file several times to find the next field to Clean. The limit on the number of fields done depends on the maximum size of the AP, the size of the images, etc - trying to guess when I/O will be expensive in time. Sometimes, IMAGR will make more images than are needed at a subsequent excess cost. To limit the number of fields imaged at any one try, set IMAGRPRM(18) to the maximum number you want to allow. The task will now reduce the maximum number when the multiple fields all have similar maxima - i.e. after the wide dynamic range early cleans are done. (19) In OVERLAP>= 2 mode, when Cleaning a field with a small bright source, it is possible to Clean too deeply. Then weak lumps due to sidelobes of strong sources in other fields are treated as sources in the present field. By the time the present field is Cleaned again, these errors become very apparent. This parameter is used to limit the weakest source Cleaned in this major cycle to IMAGRPRM(19) times the strongest source in this cycle. The default is the sum of the maximum sidelobe outside a radius of 5 pixels and the maximum sidelobe outside a radius of MINPATCH pixels. IMAGRPRM(19) is also used to limit the depth of a SDI Clean major cycle. SDI never goes deeper than 0.33 of the peak, but even that may be too much. (20) In OVERLAP >= 2 mode, the objective function of the selected field after it is re-imaged is compared to the objective function of the second best field (without re-imaging). If the second best now appears better than the selected field by a factor greater than IMAGRPRM(20), then the task will try another field. 0 = 1.005. (Values < 1 are converted to 1/IMAGRPRM(20) and, finally, values > 5 => 1.005.) IM2PARM....Even more IMAGR parameters: Auto-Clean boxing (can be changed by TELL): (1) IMAGR can create Clean boxes automatically. In OVERLAP 2 mode it will do this only in the facet about to be Cleaned. In OVERLAP < 2, it looks at every facet at each major cycle. It will find no more than the strongest IM2PARM(1) boxes each time it looks. <= 0 => don't do. Limit 50. (2) The auto-boxing starts by finding islands of emission > IM2PARM(2) * rms in the residual image. This defines the size of the box if it is accepted. (0 -> 3.0) (3) A box can only be accepted if its peak brightness is > IM2PARM(3) * rms in the residual. A box is also accepted only if the peak in it is not already in a Clean box. < IM2PARM(2) -> IM2PARM(2) + 2.0 (4) A box is also only accepted if its peak brightness is > IM2PARM(4) * maximum residual in the whole image. < 0.01 OR > 0.9 -> 0.1 (5) The box determined by the island may be extended outward in all directions by IM2PARM(5) pixels. < -1 => 1. Note that -1 means compressed by 1 in radius or in all directions for rectangles. (6) The residual image is examined only in an ellipse (circle if IMSIZE(1) = IMSIZE(2)) of radius in X of IMSIZE(1)/2 - IM2PARM(6) and in Y of IMSIZE(2)/2 - IM2PARM(6). <= 0 -> 5 (7) When imaging an output cube, should channel N+1 begin with the boxes of channel N or only with those set up by BOXFILE, CLBOX, etc.? > 0 - begin with initial boxes in each channel < 0 - pass boxes along to next channel = 0 => +1 when auto-boxing, -1 when not doing auto-boxing TV timeout controls: (8) The first TV display resumes Cleaning after IM2PARM(8) seconds. 0 -> 600 (9) After the first, the TV display resumes Cleaning after IM2PARM(9) seconds. 0 -> 30. Baseline-depndent and frequency averaging: (11) The maximum elapsed time over which averaging of data may be done in seconds. 0 -> infinite (12) The desired field of view radius in arc minutes which is not to be distorted by time averaging in a baseline-dependent fashion. <= 0 -> infinite or no averaging. The field of view is the region in which averaging is not to reduce the amplitude by more than 1% on any baseline. No data separated by more than 268.5 wavelengths divided by IM2PARM(12) are averaged together. It might be wise to make this parameter larger than the field of view about which you care. (13) Average IM2PARM(13) channels together in the on-the-fly averaging when IM2PARM(12) > 0. Note that you can get channel averaging without time averaging by setting IM2PARM(11) to a small enough (but > 0) value while setting IM2pARM(12) to an appropriate value. If IM2PARM(13) is 1, IMAGR will compute the number of channels based on the maximum possible baseline and the value of IM2PARM(12). This parameter must be <= NCHAVG and both NCHAVG and CHINC should be integer multiples of IM2PARM(13). Future expansion: (10) (14) - (40) NGAUSS.....Number of scales to use. 0 -> WGAUSS=0 and NGAUSS = 1. The total number of scales is NGAUSS and the total number of fields imaged will be NFIELD*NGAUSS. Clean boxes specified for fields 1-NFIELD will be copied to the corresponding fields NFIELD+1 to NFIELD*NGAUSS unless (using BOXFILE) you have specified them already. RASHIFT, DECSHIFT, FLDSIZE are specified only for fields 1-NFIELD. See multi-scale Clean discussion in the Explain section. WGAUSS.....The FWHM of the circular Gaussian source models to be used. If a point source is to be used (which is recommended), then WGAUSS(1) should be 0 and WGAUSs(2) through WGAUSS(NGAUSS) > 0. IMAGR will go through the widths to insure that, if a WGAUSS of 0 is used, it is the first one. All resolutions now have components from all resolutions restored to them scaled appropriately with the widths of the fatter of the two resolutions. FGAUSS.....The minimum flux in Jy/beam for each scale in the same order as WGAUSS. Must be >= FLUX to have much effect. MAXPIXEL...The maximum number of pixels that are searched for components inside the ``AP'' in each major cycle. <= 0 => 20000. This number affects the cpu usage significantly. Too many causes the task to search over many points it will never use. Too few causes the task to do many more small major cycles, also at great expense. Use this with great caution, but big wins are possible using larger sizes on very large Cleans. OVERLAP=2 mode may need speeding with FACTOR > 0 and/or larger MAXPIXEL. IN3NAME....Image name of spectral index image; no default. IN3CLASS...Image class of spectral index image; no default. IN3SEQ.....Image sequence of spectral index image; 0 -> highest. IN3DISK....Disk of spectral image image; 0 -> any. IN4NAME....Image name of spectral index curvature image; no default. Curvature images should be base 10 rather than base e - they differ by a factor of 2.3. Also the reference frequency for them is 1 GHz. These are changes done 2010-07-13. IN4CLASS...Image class of spectral index curvature image; no default. IN4SEQ.....Image sequence of spectral index curvature image; 0 -> highest. IN4DISK....Disk of spectral curvature image image; 0 -> any. FQTOL......Frequency tolerance in kHz. Spectral channels with FQTOL are handled together (use the same average CC model) when applying the primary beam and spectral index corrections. Default is to do each channel separately which can take a long time. DOTV.......Display residuals on TV channel 1. > 0.5 => display field number DOTV initially. Can be changed interactively and by TELL. When using this option, you may interact with the residual images, selecting which field is examined in what window, resetting the Clean boxes, and stop the Cleaning of the current channel. IMAGR uses DOTV in the form of the nearest integer; set it only to integer values. BADDISK....This array contains the numbers of disks on which it is desired that scratch files not be located. BADDISK has no effect on input and output maps. ---------------------------------------------------------------- See EXPLAIN IMAGR for more information on the imaging parameters.