(a) Shadow and shading images used for 3D reconstruction of lunar crater
Theaetetus. Illumination angles are μ = 17.9° (May
20, 2002), 12.2° (December
12, 2002), and 15.0° (July 30, 2002).
The region inside the rectangular box is reconstructed. To the right the
shading and shadow images simulated based on the reconstructed 3D profile are shown, which
correspond well with their real counterparts. The shadow images were rendered
using the raytracing software POVRAY.
(b) Area between the two shadows, used for initialisation of the surface profile.
(c) Lunar Orbiter image IV-110-H2, shown for comparison. (d) Reconstructed 3D
profile of the eastern half of crater Theaetetus. Even the ridge crossing the
crater floor, which is visible in the upper left corner of the region of interest
and also in the Lunar Orbiter photograph IV-110-H2, is apparent (arrow).
Furthermore, it turns out that the crater floor is inclined from the north to
the south, and a very shallow central elevation rising to about 250 m above floor
level becomes apparent. This central elevation does not appear in the images used
for reconstruction, but is clearly visible in the ground-based image acquired on
June 09, 2003, at a higher solar elevation angle of
μ = 28.7° shown in (e) (left, lower arrow). The simulated image (right
half of (e)) obtained by applying the same illumination conditions to the
3D reconstruction result shown in (d) is very similar to the corresponding
part of the real image although that image has not been used for reconstruction.
This kind of comparison is an independent test of reconstruction quality.
For comparison, traditional shape from shading yields an essentially flat
crater floor and no ridge (f).
