Very slow-moving robotics, according to a documentary which aired
here earlier this year.... what's equally amazing is the fact that they
actually built a roof & walls around some sections of terrain that
they were photographing (for example, the bluebell wood), so that
fluctuations in weather & light didn't detract from the
sequences.. you'd never guess from looking at the finished edits, but
many sequences were actually shot "indoors" under banks of artificial
light!!
-Shep