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The psrotate utility is a Python program that performs basic manipulations on PostScript files. It is particularly intended for treatment of files generated by the GEMPAK postscript driver. The program works by directly hacking the image file itself rather than converting image formats - this ensures that there is no loss of plot quality during the rotation or resizing processes. psrotate can be used to rotate images, shift an image on a page, rescale images and/or change the page size.

UPDATE - 2 April 2006: Matt Borkowski (NCSU) reported that the psrotate tool did not work on black and white PostScript files generated by GEMPAK. This problem has been fixed, and an updated version of the software is available for download (left shift and click for download).

psrotate runs from the command line of any machine with Python installed. Following installation (which is as simple as downloading the program into a directory found by the user's path - optionally the first line of the program can be edited to the correct Python path for the local machine), the user should become familiar with the psrotate options by running python psrotate.py -h. Note that if the correct Python path is present at the top of the program, then simply running psrotate.py -h. From here on it will be assumed that the path is correct - if it isn't then you will have to prepend the python command to each of the examples below.

The only required argument is the -f FILENAME argument (it can also be written as --file=FILENAME) that gives psrotate the name of the input PostScript file. Optionally, a -o OUTFILE (or its long form) can be given to set the output file name. By default, the output file is named the same as the input file with a -rot appended. All other arguments are optional - note that it you are running psrotate on GEMPAK files, then running with the -O 1 optimization flag is extremely beneficial.

The default operation of psrotate is to create a fitted landscape PostScript image from the default GEMPAK rotated plot. (This rotated image can then be converted to a PNG file using GhostScript for extremely high-quality web-ready images.) To perform this operation, simply run psrotate.py -f INPUT.ps. The output will be generated in INPUT.ps-rot where the value of INPUT depends on the image file name. This file can then be converted to a high-quality PNG image using gs -q -sDEVICE=png256 -sOutputFile=OUTPUT.ps -dNOPAUSE INPUT.ps-rot -c quit where both INPUT and OUTPUT depend on the image file name.

To make the PostScript image smaller without any conversions, the user might run something like psrotate.py -f INPUT.ps -o OUTPUT.ps -s .8 -p 610x500. Note that the page size is given in pixels and that the -O 1 option should be used if the source file is a GEMPAK PostScript. Other rotations are also possible, for example psrotate.py -f psc.plt -o ron.ps -O True -l 2.5 -r 20 -p 850x820 create (for whatever reason) an image rotated by 20 degrees from horizontal. The standard Letter page size is 612x792 so this paper size should be specified if the image is to be printed on letter-sized paper.

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