• Below are illustrated some simple, common tasks. Note that NCAR graphics is implemented as a batch system. This means you look at the graphs after the program is run and you cannot interactively modify the plots.

• I have created some executable files that you are welcome to use as templates for the two common types of plotting described below.
  
  IMPORTANT NOTE!
  • Each .f file referenced below is a file of FORTRAN statements. To run the file you do the usual ncargf90 command followed by the ./a.out command.
  • Each .for file referenced below is a complete program surrounded by unix scripts; the unix scripts make the file self-executable. To run, you just type ./filename However, the file permissions must be set to allow execution (with a chmod statement). You could edit your copy to remove the unix scripts, thus making a regular file of FORTRAN statements; to do so, you would remove every line that starts with #. Also, these .for files are likely in Fortran 77 and may no longer work properly in F95.

• setting up your environment
  • NCAR graphics uses the gks system and that must be started before any plot commands. There are several ways to do this, the simplest is the fortran line:

    call opngks !place before any plotting routine calls

    Next you have to map x,y ranges to the screen coordinates. By default the screen coordinates go from 0 to 1 in both the x and y dimensions, as measured from lower left corner. Example:
    call set(0.1,0.9,0.2,0.8,-10.,10.,-5.,5.,1)
    ! this call uses 1/10 to 9/10 of the way across screen in x (Left to Right)
    ! this call uses 2/10 to 8/10 of the way across screen in y (going bottom to top)
    ! this call maps x range from -10 to +10 to the range of 1st 2 arguments.
    ! this call maps y range from -5 to +5 to the range of 3rd & 4th arguments.

    ! fortran code, including your plot calls go in here....

    call frame ! advance to next 'frame' as if your plots are going onto a strip of film
    Note that you may call frame multiple times to create multiple plots. Each call dumps the plot buffer created since the last prior call to frame, or start of your program.

    call clsgks !place after all plotting routine calls

  • A FORTRAN 90 example is in file: demo_ptline.f

• plotting symbols and text
  • NCAR graphics has many ways to plot symbols and text. Here is a basic example:

    ! must assign a character variable to put your encoded text
    character*10 chrs ! variable chrs can hold 10 characters

    to write a variable and a label:
    t=3.5 ! anything that fits the format in the write below:
    write(chrs,'(6htime = ,f4.2)')t
    ! the write statement should encode "time = " then value of t in format f4.2
    Now plot the character string at the location xl, yl which should appear on your plot where you mapped the x,y ranges with your set call.
    call plchhq(xl,yl,chrs,16.,0.,0.)
    

  • A FORTRAN 90 example is in file: demo_ptline.f
  • plchhq can do a large range of greek letters, weather symbols, sub/superscripts, etc. See the Atmospheric Science Program's computing resources webpage
    ncarintro2.htm *** link may be broken ***
    PLCHHQ character codes.
  • NCAR's PLCHHQ web page where you can access examples that show the character codes.

• plotting a line
  • NCAR graphics has several ways to plot a line(s). Here is a basic example:

    ! assume a set call has been made such as:
    call set(0.,1.,0.,1.,0.,1.,2.,4.,1)
    ! Notice that the entire screen scales with these ranges: 0. <= x <= 1. and 2. <= y <= 4.

    ! draw a horizontal line from the middle to the top
    call line(0.5,3.0,0.5,4.)

    ! draw a diagonal line from the middle to the lower left corner
    call line(0.5,3.0,0.,2.)
    

  • A FORTRAN 90 example is in file: demo_ptline.f

• creating a line drawing.
  • NCAR graphics has many ways to create line drawings (f(x) versus x). A simple way to place several lines onto one graph is illustrated by the following call:
    CALL EZMY(PL,M,4,M,13HFINAL VALUES$ )
    This call plots 4 lines from array PL(M,4), and places a label at the top that says: "FINAL VALUES".
  • There are other similar "easy" ("EZ") routines in NCAR graphics that do basic plots easily. This is just one example. (The "EZ" routines automatically call graphics "primitives" such as SET and FRAME)
  • A FORTRAN 77 template for this procedure is file: line.for

• creating contour plots
  • NCAR graphics has many ways to make contour plots depending upon the smoothness of the lines desired, whether the data is at evenly-spaced grid points, etc.
  • A FORTRAN 77 template showing how to make a basic contour plot is in file: contour.for
  • A FORTRAN 77 template for contour plotting of randomly-located data point is in file: random.for

• viewing a plot
  The easiest way is to use the facility "idt".
  • For example, if your metacode file is titled MYMETA.PLT, then the command is just
              idt MYMETA.PLT
  • A pair of windows will appear with simple "buttons" to click for displaying and printing of graphics frames.
  • The facility idt is a simple interface to "ictrans" commands. There is some value in learning ictrans if you are working remotely and displaying your terminal link using an x-windows emulator is slow or not available.
  • Note: by default NCAR graphics makes the metacode file named gmeta.

• Some general comments
  • The "plot primitives" that you might be likely to use are: SET, GETSET, FRAME, LINE, GRIDAL, and LABMOD.
  • The graphics "utilities" are a bit higher level routines that call set up calls to the primitives. Utilities you are likely to use are: CPCNRC, PLCHHQ, EZMAP, and various AUTOGRAPH routines.
  • Program "line.for" mentioned above uses AUTOGRAPH calls as well as plot primitives (SET, FRAME, & LINE).
  • For example, program "contour.for" mentioned above uses CPCNRC and PLCHHQ commands and plot primitives SET & FRAME.
  • Other commonly used utilities are: ISOSRF, SRFACE, STRMLN, THREED, VELVCT, and WINDOW.
    If you plan to use NCAR graphics in the future, you are encouraged to be aware of what these routines can do.

Back to ATM 150 homepage