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$^{st}$ 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