Thin lines in pdf file displayed on mac

Question

Hi,
I don't know if this is the right place to bring this up.  So redirection elsewhere is appreciated!
I've noticed a problem with displaying certain pdf files on a mac.  The files are 2D filled plots produced by the free scientific software Yorick (http://yorick.sourceforge.net/).  It happens when I view it in Preview or Powerpoint on a mac.  But not if I use a pdf viewer on a unix system.  The yorick source code for a simple example is below.  I can't find a way to attach files to this messages or I'd include the pdf's.  Is there a way to do this?
Both png's are fine, and the pdf of the pli plot is fine.  pli assumes uniform grid spacing, is fast, and must use different graphics primitives than plf, which does not assume uniform grids (i.e. you can have non-square elements).  In this case both x and y grids really are uniform.  The problem is with the pdf of the plf plot.  Look at it in Preview, you should see some thin lines.  Put it in powerpoint and the same.  If you put some solid colored box in back of it, you'll see the color.  So the lines are transparent or something.
David Munro, the creator of Yorick, suggests it's an issue with anti-aliasing.
Anyway, the problem isn't that severe in this example, but in others (which don't have simple source code) it's more annoying. 
Either way, any advice on this, or the right people to report this to, is appreciated.
Cheers,
David
// 10dec10: bug of contour plots in pdf's having white lines on mac
x=span(0,3,21);
y=span(-2,2,30);
x2 = x(,-) + 0*y(-,);
y2 = 0*x(,-) + y(-,);
z2 = exp(-x2^2-y2^2);
fma;
palette,"rainbow.gp";
pli, z2, x(1),y(1), x(0),y(0);
cd,"~/yorick/pdf-mac-bug";
pdf,"pdfmacbug_pli.pdf";
png,"pdfmacbug_pli.png";
fma;
palette,"rainbow.gp";
plf, z2, y2,x2,;
cd,"~/yorick/pdf-mac-bug";
pdf,"pdfmacbug_plf.pdf";
png,"pdfmacbug_plf.png", dpi=150;

Answer 1

As I suspected, the problem is that the other viewers are not savvy enough to handle the "stitching problem".
What looks like a single image is really a WHOLE LOT of single squares.  I took a snapshot of the Edit Object tool in Acrobat with all the objects selected.  See <https://photos-3.dropbox.com/i/o/R6asqv64sEP1Tf7eIEBfNbFbMw0F7qKEaFwfnXQVKLo/1644474/12950 96400/0fa9181>.
As you can see from that, each square is a separate image that needs to be rendered and if the viewer doesn't understand how to proper stitch the pieces together then you will get empty pixels (which appears as white lines).
Either contact the author of the program that authored the document and see about getting that fixed (if it's not you) and/or contact the other viewers about improving their products.