Documentation for cmap.gs -- GrADS Color Table Script 

(M. Fiorino) 

Note: In the text below strings between the ' ' are GrADS command and
strings between " " are UNIX commands or files names.

This script allows you to interactively create and modify a color table. 

I use the .gct file postfix to distinguish GrADS color tables from
other GrADS files (e.g., .gs = GrADS scripts) and at the first
invocation of cmap.gs, the a color table called "grads.gct" is
created. I typically rename grads.gct to another file name (e.g.,
nmc.gct) and then use that table in subsequent scripts.

Let's create a color table. First fire up GrADS in landscape mode

     grads -l

resize your graphics window and at the GrADS terminal window type,

     run cmap.gs

The first thing the script will say is,

     Enter the Number of Colors:

Type in a number between 1-100, for example,

     10

You should then see on the graphics screen (--> explains what's what): 

     GrADS color table for : grads.gct --> name of the color table file 
     (10 boxes) --> boxes with color to edit 
     1 2 3 4 5 6 7 8 9 10 --> number of the box 
     1 --> color number being edited

       ---      ---      ---

        |        |        |

        |        |        |

        |        |        |          -->  sliders to control R G B

        |        |        |

        |        |        |

        |        |        |

        |0       |0       |0         -->  the value of R G B

       ---      ---      ---

     |--------|

     | Save & |         -->  box to click to save and quit

     |  Quit  |

     |--------|

To edit color #2, use your mouse and click on the box above number
2. The color number will change to 2 and you're ready to edit. Click
just to the left of the slider to change the value. The bottom part of
the slider is 0 and the top is 255. Just play with each slider until
you are happy with the color and go on to another color.  Repeat the
"click to the left of the slider process" and when you are all done,
click on the save and quit button. This will save your color table to
the file "grads.gct". Here is what it will look something like:

     1 225 174  91 
     2 238 214 129 
     3 163 233   0 
     4   0   0  88 
     5   0 201   0 
     6   0 213 107 
     7 240 192  69 
     8 233 144 227 
     9 221 192 109 
    10 247   0   0

To access these colors in GrADS use the colortab function provided at
the end of doc. Here's how the "grads.gct" file color table is
accessed in a GrADS script:

     rc=colortab(grads)

rc is a return code and equals the number of colors in the color table
file "grads.gct", if the file was there and was readable. Note that
the ".gct" in the file name is implicit. Even though the numbers are
referenced 1-10 in cmap.gs, in GrADS the colors are numbered as
21-30. The starting number of the color table is arbitrary; I chose 21
to separate user-defined colors from the 0-15 GrADS default colors
which cannot be changed.

To use the colors try something like,

     set gxout shaded
     set clevs 1000 1004 1008 1016
     set ccols 0 21 22 23 24

Undoubtedly you will not be happy with your first color table. To edit
it, just rerun cmap.gs, but use the file name as a command line
parameter to cmap.gs, e.g.,

     grads
     run cmap.gs. grads

The color table will be read in and you can now edit the colors and
save it. However, cmap.gs will overwrite the file, so copy it to
another file if you want to keep the original.


Problems and questions: The colors do not come out right on a PC
running Xvision during editing, but not when running GrADS. The
problem is in the X server because when you have draw color 20 on the
screen and then, set rgb 20 to a different color, it changes on the
screen (the difference between pseudo and true color in X).