velplotc is a neat program to create position-velocity slices from a miriad cube. It will output a miriad image. It is a graphical frontend to the velplot program, which does the same, which is instead driven by Mel Wright's famous interactive command input. Chin-Fei Lee wrote this program when he was a graduate student at Maryland. The GUI interface in velplotc is arguably a little easier to use,however the installation is not for the faint of heart.
velplotc may not have been installed on your system. The most likely cause is the absence of a freely available library called XForms (see  or ). If you are lucky, your linux distribution or method of enhancing your mac will come with a pacakge/port for this. For example, on my Fedora9 distribution i typed: yum install xforms xforms-devel. If not, you will have to install it. One telltale sign if it is installed is to find the header file forms.h (e.g. locate forms.h), or the library libforms.a.
Apart from resolving where the library is, you may wind up having to increase MAXBUF in the private version of mem.h in the source code for velplotc. Here's a snippet of shell code how you can (re)build velplotc:
cd $MIR/src/spec/velplotc edit mem.h (may also need to check $MIRINC/maxdim.h and maxdimc.h) make clean velplotc LIBFORMS=$MIRLIB/libforms.a FC=g77 mv velplotc $MIRBIN
in this example I choose to hardcode the location of the library inside of MIRLIB itself. It might very well live in /usr/lib or /usr/local/lib, in which case you will probably not need to override the LIBFORMS macro. For more details, see the Makefile in that directory.
Just typing the command velplotc will remind you to the command line arguments. There is no out=, the name(s) of the image(s) are hardcoded.
velplotc in=n6503.sub task=doposvel device=/xs cut=0,0,120
would create a pos-vel diagram centers on the reference pixel, at a PA of 120 degrees. The output file is 'pos001.map'.