function gte_midtime,data,vardesc,local_time=local


    ; *** future options? JULTIME ?

    minval - -1.E30


    ; test if data is valid and contains at least 4 variables
    if (n_elements(data) lt 2) then return,minval

    s = size(data)
    if (s[0] ne 2 OR s[2] lt 4) then begin
        message,'Data not 2D array or too few variables!',/CONT
        return,minval
    endif


    ; local time requested ?
    local = keyword_set(local)


    ; Test if required variables are there
    selind = ['JDAY','STARTHOUR','STARSEC','STOPSEC']
    if (local) then selind = [ selind, 'LON' ]
    if ( (make_selection(vardesc.name,selind,/REQUIRED))[0] lt 0 ) then begin
       message,'Required variable not found!',/CONT
       return,minval
    endif


    ; Here, we assume that the first 4 variables are JDAY, STARTHOUR,
    ; STARTSEC, STOPSEC

    starthour = data[*,1]
    startsec = data[*,2]
    stopsec = data[*,3]

    ; compute midtime as UTC time
    result = 3600.*starthour + 0.5*(startsec+stopsec) 


    ; compute local time if requested
    if (local) then begin
       ; get longitudes
       lon = data[*,where(vardesc.name eq 'LON')]
       result = result + (lon/15.)  
       ; make sure it's within a day's range
       result = (result + 86400.) mod 86400.
    endif


    return,result

end