Plot Devices

Only a few tasks make use of the TV server, but there are many more that use PGPLOT for their graphical display. PGPLOT devices cannot be zoomed or panned, but they can be used to return quantitative information from the display (coordinates, values). In addition, it is possible to interactively modify the lookup table and transfer function of some PGPLOT devices (notably the X-window devices) in software. See Chapter 16 for a discussion of which tasks of this capability.

PGPLOT devices are specified by the standard PGPLOT specification and are assigned to the MIRIAD keypwrd device. The specification has two parts separated by a /: these are the name and type parts.

The name part either gives a device name (usually for graphics devices) or a file name (usually for hardcopy devices, such as postscript printers). In the case of a file name, any normal file name can be given. However if it contains a / character, then the entire file name should be enclosed in double quotes ("). Once a file has been created, you will generally have to issue operating system commands to spool this to the appropriate output plotter, etc. The name part can often be left blank -- it defaults to something sensible. The most common case where you do not let it default is when you are specifying a disk plot file.

The type part tells PGPLOT what sort of graphics or hardcopy device is being used. Minimum match is used. Some possible types are:

xs

This is a resizable and persistent X window.

xw

This is a transient X window.

xd

This is the pgdisp X windows server.

re

A VT100 with RETROgraphics card.

v603

A V603 terminal.

krm3

A Kermit 3 IBM-PC terminal emulator.

tek

A TEK 4010 compatible terminal (or window).

ps

PostScript. PGPLOT will write the plot as a disk file in PostScript form. At ATNF sites, you can print this postscript file with the command:

% lwp filename

vps

Vertical PostScript. The only difference between this and ps, is that vps generates a plot in portrait mode, whereas ps is in landscape mode.

cps

Colour PostScript in landscape mode.

vcps

Colour PostScript in portrait mode.

null

The null device. Useful for debugging when you do not have a display.

Examples of PGPLOT devices are:

• device=4/xs directs output to the persistent X window number 4 (you can have many of these windows)
• device=/xw directs output to the transient X window.
• device=plot.ps/ps create a PostScript plot file called plot.ps
• device=/tek assumes you are working at a Tektronix 4014 terminal. Graphics output is directed to your terminal.

Another useful pseudo-PGPLOT device is ?. This causes a complete list of PGPLOT types to be printed, and then the task will prompt you to give a PGPLOT device.

When plotting in an X window, you must meet the conditions which allow PGPLOT to communicate with your X server. In particular:

• You should be working at a workstation running X windows.

• You do not need to run the MIRIAD plotting task on the same computer as the X-windows server. However if you are running on a different machine, then you will need to tell PGPLOT which machine is running your X server. To do this, issue the command

  % setenv DISPLAY localhost:0

  to the machine you are running MIRIAD tasks on. Here localhost is the name of the host machine running X windows. Normally this will be you local workstation.

• X windows has a simple security feature to prevent arbitrary people drawing plots on your screen. To authorise a particular machine to send commands to your X server, you will need to issue the command

  % xhost + remotehost

  to your local host. Here remotehost is the name of the host machine that you want to grant permission to. For MIRIAD applications, this will be the host you are running the plotting task on.

PGPLOT has two X windows servers, and as of PGPLOT V5.0, one of which ( pgdisp) is deprecated. The PGPLOT device types /xs and /xd are now mediated by a server (called pgxwin_server). This server is automatically started whenever either of these devices is invoked. The /xs windows are permanent and resizable whereas the fixed size /xw windows disappear as the application terminates. This server allows multiple windows and you can choose to write to whichever one you like (see above example). The resources for these windows are managed through the standard X windows resource file; see the PGPLOT manual for details of these issues.

The deprecated server, pgdisp, which creates a resizable persistent X window is started by hand with a command such as

% pgdisp &

from a workstation window (usually the console window). This window is written to with the keyword device, see below). This window can be used for line graphics as well as grey scales. By default, the pgdisp window only has 16 colour levels, which is insufficient for most image display applications, but fine for line graphics.

If you start it up with the command

   % pgdisp -lineColors 128  &

then the window will be allocated 128 colours which is sufficient for imaging applications. This window is much slower than the windows mediated by the pgxwin_server. In addition you can only have one.