### 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.