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Complex or frequently used keyword constructions or logical expressions can be abbreviated to ARCQUERY symbols. Such symbols can be used as shorthand or alternative keyword names. For example, if you define the symbol NLSEL as:
NLSEL = "SEL/NOLIST/FILE" ,
then the subsequent instruction:
NSEL OBJE=N*4151* is equivalent to: SEL/NOLIST/FILE OBJE=N*4151*
Carefully constructed symbols can greatly simplify a complex search. As an example, consider the search for direct images in a particular waveband, taking into account that there are several imaging instruments available. Define two symbols, e.g. IMAGES, and VBAND, as follows :
IMAGES = "INST=(FWHL,PFCU,PRIME,CASS.AUX.PORT)"
VBAND = "(WAVEBAND=V | OBJECT=* V *)"
The VBAND construction takes into account that some images have no waveband information (yet; see section ), but then may have the filter name added to the object title. With these symbols defined, the search for V-band images of some object is done with:
SEL/INP=0 IMAGES & VBAND & OBJECT=..... & POS=(......
Another example of the usages of symbols:
SYM1 = "posi=(12:10:32.29,39:24:29.60, 4.2 arcmin)"
SYM2 = "posi=(00:42:44.50,41:16:28.94,60.0 arcmin)"
SYM3 = "posi=(01:33:53.79,30:39:01.72,36.6 arcmin)"
SELECT/LIST (SYM1 | SYM2 | SYM3)