Unisys Difax Postscript Charts

        John Nielsen-Gammon at Texas A&M asked how we make hard copy
difax maps from the Unisys difax images. Here's what we do at Scripps Institution of Oceanography, but keep in mind that Scripps does NOT have a teaching load, so we don't print many maps and print none routinely:

        (1) xv -rv <filename>             '-rv' reverses video and the
                                        Unisys difax comes up white
                                        on black if we don't do this.

        (2) bring up 'xv controls'      This is a 'right button' click
                                        on an Ultrix workstation.

        (3) select save                 In this example, I'm using the
                                        95032412Z US surface map which
                                        is 459,670 bytes in size.

        (4) select postscript

        (5) select Save at normal size  NOTE: This is VERY important!
                                        If you do not do this step, xv
will create a a postscript file with reduced resolution!

        (6) select B/W Dithered         This should be the default, if
                                        not, select it.  Doing this,
                                        the output postscript file was
                                        1,308,374 bytes.  Using any of
the other options increases output size by a facter of 24!
                                        Full Color = 31,334,490 bytes!

        (7) select an output filename

        (8) select OK

        (9) select paper size

        (10) select orientation

        (11) select Maxpect             This will give you the maximum
                                        size undistorted map xv thinks
                                        your printer can produce.

        (12) select OK

        Using this procedure, the output postscript file had 180 dpi
        resolution on 11" x 17" paper printed on our DEC LPS20 laser
        printer.  The printed map is very readable.  It is considerably
better than anything I ever saw come off an Okidata 293. If you don't select 'Save at normal size' however, you get an unreadable and useless 63 dpi.

        When I selected 8.5" x 11" for the paper size, xv produced
        a 288 dpi map.  The printed product is crisp, clean, and (if
        you have a magnifying glass) perfectly readable.  However,
        remember that xv will allow you to crop the image before you
        create the postscript file.  You can then print only the area
        you're really interested in and be able to read it without a
        magnifying glass.

        I think the printing time for each of these products will
        depend more on the speed of your printer than anything else.
        Typically, a 180 dpi US surface map printing on 11" x 17"
        paper takes approximately 3 minutes on our LPS20.  It may
        take significantly less time than that, but the printer is
        down the hall in the printer room and it's usually finished
        by the time I go to get it.

        We don't print maps routinely anymore because everyone here
        has a workstation sitting on their desk, even the students
        (all of whom are graduate students, and not many of those).

        Larry