R help - Jul 2008 - Lattice wireframe: How to avoid drawing lines around polygons when using shade=TRUE

I am using wireframe from the lattice package, with the shade option set 
to TRUE. When I output to PDF or Postscript, a line gets drawn around 
each polygon of my surface which causes ugly Moir? effects and doesn't 
make sense in my application (think the plot of Maunga Whau--gridlines 
don't make sense). This does not happen when I display on the screen--
then I just get the surface as intended.

I have tried everything from playing with trellis.par.set() to changing 
the code of panel.3dwire, but nothing seems to remove these gridlines. 
Any idea would be greatly appreciated.

Best,

	Oliver

On Sun, 27 Jul 2008 05:00:48 +0000, Oliver M. Haynold
wrote:
> I am using wireframe from the lattice package, with the shade option set
> to TRUE. When I output to PDF or Postscript, a line gets drawn around
> each polygon of my surface which causes ugly Moir? effects and doesn't
> make sense in my application (think the plot of Maunga Whau--gridlines
> don't make sense). This does not happen when I display on the screen--
> then I just get the surface as intended.
I have done some research on the problem. On inspection of the PDF file 
generated by lattice, it turns out that it does not actually contain any 
instructions to draw lines between the triangles of the surface plot. 
Yet, Evince and Acrobat Reader both show these lines, with disagreeable 
consequences for printing and screen display. Ghostscript, however, does 
not and renders the surface as a solid block, as it should be. Thus, a 
workaround for the problem is to put the file generated by lattice 
through Ghostscript and to convert it into a high-resolution image file.

The most likely reason for the problem I can think of is that the 
triangles generated by lattice don't overlap but just border each other. 
This might cause some renderers to leave a little space between them. If 
this explanation is correct, a solution would be to have lattice, or 
specifically wireframePanelCalculations, plot the triangles with a tiny 
bit of overlap.

Best,

	Oliver