function ser_dset, rmap, which, unser=unser, range=range, absolute=absolute
;
;+ 
;   Name: ser_dset
;
;   Purpose: return data set array for given sxt sequence serial number
;
;   Input Parameters:
;      	rmap = sxt roadmap or sxt index record
;   	which = desired data set - the interpretation is:
;	   	relative data set if absolute not set
;		absoulute data set if absolute keyword is set
;	absolute = if set, then returned data set corresponds to the
;	    	 absolute serial number - otherwise, returned data set
;	 	 vector corresponds to relative serial number 
;   Output:
;	function return value is requested data set vector
;		a return value of -1 indicates requested data set is
;		out of range 
;	range (optional key word) 2 element vector containing first and
;		last serial numbers - absolute or relative depending upon the
;	   	state of the absolute keyword
;	 
;
;-
absolute = keyword_set(absolute)
;
if n_elements(rmap) eq 1 then uniq_sers=[1] else $
   unser = uniq(rmap.serial_num) 
range=[min(unser), max(unser), n_elements(unser)]
dset = where(rmap.serial_num eq $
	rmap(unser(which)).serial_num)
return,dset
end