- Although the two projection matrices define the converse is not true.
- Suppose
and
are two matrices consistent with
, then
and
- But, if
is any arbitrary homography of 3-space, then
and
- Thus, we can only recover projective structure modulo an unknown homography.

**How to recover
, the homography that upgrades the
projective structure to Euclidean?**

Subhashis Banerjee 2008-01-21