Is there a straight forward 3D sketch tool capable of producing wireframe vector images? [duplicate]

Possible Duplicate:
How to render 3D models as SVG vector graphics? (planar projection)

Inkscape features a nice mode to create isometric projections of three dimensional images. The results can be exported nicely as SVG or PDF. For many applications this is preferable over a rendered bitmap image (as produced by Blender, POVray, etc.).

Also, vector graphics appear more technical and less playful, which looks more professional depending on the context. And finally, vector graphics are more suitable for post-processing.

However, Inkscape's axonometric grid method has a number of disadvantages:

• The viewpoint is fixed. Once, you have setup the grid, it is not possible to rotate the scene.
• I cannot figure out how to draw a sphere.
• Inkscape has no concept of front and back, so you have to manually hide or dash lines that would be invisible. (Or use opaque objects and manually get the order right.)
• Inkscape doesn't have any concept of three dimensional space at all. The whole thing remains a 2D vector graphic, which if well-done creates a three-dimensional impression.

Is there something like Inkscape in 3D, where I can work with 3D objects, and create the isometric view from the 3D model. To clarify: Technically, I want a simple 2D vector graphic (preferably as SVG), that looks 3D to the human eye. Apparently Google SketchUp can produce such graphics (as PDF, which can be converted to SVG). Here is an example. I want to draw arbitrary solid shapes that automatically get a shading as if they had some simple lighting projected on them.