;
;------------------------------------------------------------------
;
pro log10f, x,n,rmin,spval
;
; Given a field x, n vals long, change field to log10 of itself
; unless a value is <= rmin. If a value is <= rmin, set that
; value to spval. (if a value is already spval, leave it)
;
for i=0,n-1 do begin
  if (x(i) ne spval) then $
    if (x(i) le rmin) then x(i) = spval else x(i) = alog10(x(i))
endfor
return
end