Projections detect information about the size, geometric arrangement, and dimension
of sets. To approach this, one can study the energies of measures supported on a set
and the energies for the corresponding pushforward measures on the projection side.
For orthogonal projections, quantitative estimates rely on a separation condition:
most points are well-differentiated by most projections. It turns out that this idea
also applies to a broad class of nonlinear projection-type operators satisfying a
transversality condition. We establish that several important classes of nonlinear
projections are transversal. This leads to quantitative lower bounds for decay rates
for nonlinear variants of Favard length, including Favard curve length (as well as a
new generalization to higher dimensions, called Favard surface length) and
visibility measurements associated to radial projections. As one application, we
provide a simplified proof for the decay rate of the Favard curve length of
generations of the four-corner Cantor set, first established by Cladek, Davey, and
Taylor.