Keywords: greg

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### Bitmap display of images

The `PLOT` creates a bitmap display of a 2-D images, very much like the command `RGMAP` draws contour maps. As all other commands in the GREG software, the `PLOT` command essentially works in user coordinates. The `PLOT` command is essentially used in the following way:

        Greg> SET BOX LOCATION Gx1 Gx2 Gy1 Gy2  ! Define box position
        Greg> RGDATA Varname /VARIABLE          ! Get characteristics from image.
        Greg> LIMITS /RGDATA                    ! Get limits
        Greg> PLOT Varname                      ! Plot the array in the box
    ! And then other commands
        Greg> BOX
        Greg> RGMAP                             ! Draw contour levels (...)

which shows the similarity between the `PLOT` and `RGMAP` commands.

The `PLOT` command has several options, among which the most important is the `/SCALING Type Low_cut High_cut` option. `Type` indicates which type of transfer function is desired between the image and the bitmap, and can be either `LINEAR` or `LOGARITHMIC`. `Low_cut` and `High_cut` are respectively the smallest and largest values plotted. Values below (above) are truncated to `Low_cut` (resp. `High_cut`.

Blanking values are recognized by the `PLOT` command. The values used for blanking are derived from the variable characteristics, or if not set, by the current GREG blanking, or from the `/BLANKING` option.

The `PLOT` command also has less frequently used options. See the internal help for details. The sample procedure below produces figure 3:

    SIC\DEFINE IMAGE A GAG_DEMO:SMALL READ
    GREG1\LIMITS /RGDATA A
    GREG1\SET BOX_LOCATION MATCH
    GREG2\PLOT
    GREG1\BOX /ABSOLUTE
    GREG1\LABEL "Right Ascension" /X
    GREG1\SET ORIENTATION 90
    GREG1\DRAW TEXT 1.000 .0000E+00 "Declination" 5 /CHARACTER 6
    GREG1\SET ORIENTATION 0
    GREG1\DRAW TEXT .0000E+00 1.000 "Example of PLOT command" 2 /BOX 8
    GTVL\HARDCOPY FIG3.PS /DEVICE PS GREY

Figure: An example of bitmap display in GreG.

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