Aug 22, 2006
Differences in Measurements Between OGL and PPFA
Question:
Is there a significant difference in the the way measurment values are handled in the Overlay Generation Language (OGL) qnd the Page Printer Formatting Aid? I seem to recall some difference, and I want to see if this is why there are slight differences in the positioning of some elements of my output.
Answer:
According to IBM’s document, IBM Page Printer Formatting Aid:User’s Guide, there are some differences, defined as follows:
“A difference occurs when the line spacing (set by SETUNITS in OGL and PPFA) results in the distance from one line to the next not being a whole number of pels.
Each product handles the fractional pel differently.
Because the printer cannot print parts of a pel, fractional pels cannot be represented at the printer.
When line spacing calculations result in a fractional pel per line space, the following occurs:
- OGL Carries the fractions until they add up to a whole pel, then adds it in. This results in the final spot of a repeat being within a pel of where it is expected. Therefore, not all of the spaces between rules are even; they can vary by one pel.
- PPFA Truncates the fractional pel prior to the repeat. Therefore, the spaces between the lines are even, but the total might be shorter than expected. “
The recommend method to avoid mis-matched measurements is to use PELS as the setunits value in both OGL and PPFA.
Check out the Page Printer Formatting Aid (PPFA) reference materials available from IBM at:
http://www.ibm.com/Search/?q=S544-5285&v=11&lang=en&cc=zz&Search.x=37&Search.y=11.
If you would like some additional information on PPFA Commands, or
If you would like additional information on AFP Tips and Techniques, please feel free to contact COPI at: 1-888-999-COPI.
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