You need a vectorizing application, a stand-alone like Adobe Streamline, or a built-in vectorizing app, as you would find in most vector drawing applications like CorelDraw, Illustrator or Xara Xtreme. I'm guessing Inkscape has a vectorizing function, but I don't really know.
I use Xara Xtreme, my primary raster/vector app and there is an excellent vectorizing function built within. Even allows to remove unwanted points to better smooth an object to your needs. It can even handle a photograph converted to vector format, fairly well.
Check your vector drawing app and see if one is built inside.