I just dug up an old unfinished image I was working on in Bryce, that featured a huge city I had created using image maps as height fields.
I took those image maps (originally created in Photoshop), converted them to 3ds objects in Bryce, then used PoseRay to make .obj files. Then imported them into TGTP.
Though there are no texture maps (yet), the results came out nicely. And it was really easy to make (though the original .obj file was over 500 MB!).