I've come across mappers and carto's but is there a program out there that will export a selectable portion of your map, say a really cool building you've made in minecraft to a popular 3d file format (3ds, obj dae etc) so i can render it in a physically based unbiased renderer? i use Luxrender as it's free and I once played a large part in it's bug testing about a year back.

I want to make an uber cool wallpaper of something i built a long time ago