I often have to export a 3D graphics to a PDF file, to be opened and edited with my favorite vectorial application ('m using Intaglio, on OS X). I frequently get two problems (see the picture below, as seen in Intaglio) :
3D Surfaces are usually unusable. I'm getting tons of small triangles on top of many hidden triangles, and their borders are visible like shown on the picture below. This is a mess and there's nothing I can do with that sphere.
After ungrouping, 3D curves turn out to be a huge collection of tiny bits, like shown below. Again, this is unproper for editing in my vector app (I usually want to change the thickness and color of the curve).
These problems don't occur with 2D graphics. Currently, the only -partial- solution I have is to export the picture as a PNG file at high resolution. But then I can't edit the curves thickness and colors in my vector app, so PNG (or JPG) isn't a real solution to me.
What are you doing to export 3D graphics in vectorial form, especially the 3D curves? (Actually, I rarelly use the 3D surfaces in vectorial form.)