c2--567--1---------2---------3---------4---------5---------6---------712
c     Program terrpres
c
c     -- Function:  Given latitude (degrees North) and
c        longitude (degrees East) this program
c        determines and outputs the terrain pressure in Bar.
c
c     -- Input & Output Variables

            real     lat   !latitude (degrees) (input)
            real     lon   !longitude (degrees) (input)
            real     tpdat(360,720)
                     !     1/2 degree terrain pressure data
                     !     (input)
            real     tpout !terrain pressure for input
                           !location (bar) (output)
c
c     -- Local Variables
c
            integer  ilat, ilon
            logical  normal
c
c           Read surface pressure data
c
      open (unit=1, file='terrain.txt', status='old', form='formatted')
      read (1, '(18f5.2)') tpdat
      close (1)
c
c           Input latitude and longitude
c
      write (*, *)
      write (*, *)
     1 'When prompted, input latitude (degrees) & longitude (degrees)',
     2 'and press enter:  The output is terrain pressure (atmospheres)'
      write (*, *)
      write (*, *)
     1 'For another location, repeat the process; ',
     2 'to end the program, press cntl-c.'
      write (*, *)

  100 write (*,*) 'lat, lon ?'
      read (*,*) lat, lon
      if ((lat .lt. -90.0) .or. (lat .gt. 90.0)) then
         write (*, *) 'lat must lie between -90.0 and 90.0'
         go to 100
      end if
      if ((lon.lt. -180) .or. (lon .gt. 360)) then
         write (*, *) 'lon must lie between -180.0 and 180.0'
         go to 100
      end if
      if (lon .gt. 180.0) lon=lon-360.0
      ilat = int((lat+90.5)/0.5)
      if (ilat .eq. 361) ilat=360
      ilon = int((lon+180.5)/0.5)
      if (ilon .eq. 721) ilon=720
      tpout = tpdat(ilat,ilon)
c
c           Output Terrain Pressure
c
      write (*, *) 'Terrain pressure for latitude'
      write (*, '(x, f7.3)') lat
      write (*, *) 'and longitude'
      write (*, '(x, f7.3)') lon
      write (*, *) 'is'
      write (*, *) tpout
      go to 100
c
      end