pro merc_conv,instr,gamma,az_offset,na_offset,topna,az,na,x,y

; modified 9/20/01 to do double precision
; modified 10/05/01 to not do wrap-around on SLI images whose
;   azimuth puts their edges right on the boundary (near 12 deg)

x=(az+az_offset)*!dtor
y=alog(tan((na+na_offset)*!dtor/2d0))

g=!radeg*gamma
if instr ne 'SLI' or abs(g) lt 10d0 or abs(g) gt 14d0 then begin 
  boundary_indx=where(x lt -0d0,bound_cnt)
  if bound_cnt ne 0 then x(boundary_indx)=x(boundary_indx)+2d0*!pi
endif

;stop
return
end