## Plotting source or planet position

In addition to computing the coordinates, the commands SOURCE /DRAW and PLANET /DRAW will also indicate the position of the requested source in the current plot (as defined by FRAME). Arguments to the /DRAW option may be:

- LINE, to plot a line from the previously computed position
- MARKER, to plot the current GREG marker at the computed position (with a size corresponding to the source flux in the catalog, for the SOURCE command).
- SYMBOL to plot the source name (SOURCE command) or the usual planet symbol (PLANET command)
- FULL, to combine MARKER and SYMBOL (the sourcee name or planet symbol will be offset one marker size above the computed position).

The default argument of /DRAW is SYMBOL. Another very useful option of the SOURCE command is SOURCE /FLUX min_flux, that selects only the sources whose flux is larger that the min_flux value.

Examples — Below are a few examples of plots produced by the commands described in this section. A large variety of plots can be produced, depending on the user's purposes.

The following commands plot the position of the sources in the sky at 03:00 UT on April 1 2008, together with the position of planets (Fig. , only Jupiter is up):

      CATALOG GAG_DEMO:SAMPLE.SOU           ! define the catalog
      OBSERVATORY BURE                      ! define the observatory
      FRAME HORIZON                         ! plots the whole visible sky
      TIME 03:00 01-APR-2008                ! define the time & plot sun avoidance
      SOURCE /DRAW                          ! draw all sources from catalog
      PEN 1                                 ! select pen 1 (red)
      PLANET /DRAW                          ! draw all planets
      PEN 0                                 ! select pen 0 (black)
      HEADER                                ! label the plot.

The same plot, but seen in a different projection (from zenith position, see Fig. ), is produced by:

      CATALOG GAG_DEMO:SAMPLE.SOU           ! define the catalog
      OBSERVATORY BURE                      ! define the observatory
      TIME 03:00 01-APR-2008                ! define the time
      FRAME HORIZON ZENITH                  ! plots the whole visible sky
      SOURCE /DRAW                          ! draw all sources from catalog
      PLANET /DRAW                          ! and planets (only Jupiter is up)
      HEADER                                ! label the plot.

The following commands sequence plots the phase calibrators close to NGC 7027 (Fig. ):

      CATALOG GAG_DEMO:SAMPLE.SOU           ! selects the source catalog
      CATALOG GAG_DEMO:PHASE /ALTERNATE     ! selecs the calibrators catalog
      OBSERVATORY BURE                      ! define he observatory
      TIME 03:00 01-JAN-1990                ! define the time
      SOURCE NGC7027                        ! get source position
      FRAME EQ RA|PI*12 DEC|PI*180 45       ! frame EQ, centered on source,
                                            ! 45 degrees in total size
      PEN 1                                 ! red pen
      SOURCE NGC7027 /DRAW                  ! plot source position
      PEN 0                                 ! black pen
      SOURCE /DRAW /ALTERNATE               ! draw phase calibrators
      HEADER                                ! label the plot