hmmm. I have actually generated ps files for the whole scrolled region, did a ps2png conversion and plotted them out just fine. It's when I actually specify the pagewidth or pageheight to be something that I could printout on a printer I get a portion of the diagram clipped.

Actually the problem seems to be related to moving the objects on the canvas. The ps generated seems to be of the original area where the objects were created. If I move the objects from their start point a portion of the diagram gets clipped. I was starting suspect the bbox but I use it to set my scroll region and it seams to be capturing the bounding area correctly and updates correctly as I move objects around. The width and height values calculated from bbox are correct as well. postscript just does not seem to notice that the top&left edge have changed. The more I move stuff the worse the clipping gets. I tried to compensate by specifying top&left with the -x&-y using the first two values from bbox. This helped to lock the diagram in place but there is still some small amount of clipping occassionally. This I have found out is just a problem with my ps viewer. For some reason it does not recognise the ps as letter size. If I force it to respect letter then all is good.

So it looks like a combination of issues:
1. postscript can't seem to track the top&left edge but this can be compensated for with -x&-y settings.
2. my ps viewer does not recognise the ps file as letter size.

I've added a program to my scratch pad that lets you experiment with this problem. You can move the middle box all over and print out the canvas. if you comment out the -x,-y parameters in the print sub you will see the clipping issue.

Thanks to all for your help!