SRCOR

       Correlate the source positions found on two lists.

       srcor,x1in,ylin,x2in,y2in,dcr,ind1,ind2

       x1in,y1in - First set of x and y coordinates.  The program
                   marches through this list element by element,
                   looking in list 2 for the closest match.  So, the program
                   will run faster if this is the shorter of the two lists.
                   Unless you use the option or magnitude keyword, there is
                   nothing to guarantee unique matches.
       x2in,y2in - Second set of x and y coordinates.  This list is
                   searched in its entirety every time one element of list 1
                   is processed.
       dcr - Critical radius outside which correlations are rejected;
             but see 'option' below.

       option - Changes behavior of program and description of output
                lists slightly, as follows:
       OPTION=0 or left out
             Same as older versions of SRCOR.  The closest match from list2
             is found for each element of list 1, but if the distance is
             greater than DCR, the match is thrown out.  Thus the index
             of that element within list 1 will not appear in the IND1 output
             array.
       OPTION=1
             Forces the output mapping to be one-to-one.  OPTION=0 results,
             in general, in a many-to-one mapping from list 1 to list 2.
             Under OPTION=1, a further processing step is performed to
             keep only the minimum-distance match, whenever an entry from
             list 1 appears more than once in the initial mapping.
       OPTION=2
             Same as OPTION=1, except the critical distance parameter DCR
             is ignored.  I.e., the closest object is retrieved from list 2
             for each object in list 1 WITHOUT a critical-radius criterion,
             then the clean-up of duplicates is done as under OPTION=1.
       magnitude
             An array of stellar magnitudes corresponding to x1in and y1in.
             If this is supplied, then the brightest star from list 1
             within the selected distance of the star in list 2 is taken.
             The option keyword is ignored in this case.
       spherical
             If SPHERICAL=1, it is assumed that the input arrays are in
             celestial coordinates (RA and Dec), with x1in and x2in in
             decimal hours and y1in and y2in in decimal degrees.  If
             SPHERICAL=2 then it is assumed that the input arrays are in
             longitude and latitude with x1in,x2in,y1in,y2in in decimal
             degrees.  In both cases, the critial radius dcr is in
             *arcseconds*.  Calculations of spherical distances are made
             with the gcirc program.

       ind1 - index of matched stars in first list
       ind2 - index of matched stars in second list

       none

       none

       See under keyword LEVEL above.

       Adapted from UIT procedure  J.Wm.Parker, SwRI 29 July 1997
       Converted to IDL V5.0   W. Landsman   September 1997

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