Projective sampling under orthographic projection

[ejtwe]

How can projective sampling be extended to compute differentiable gradients under orthographic projection, and to optimize geometry? This should also be an interesting question.

[njroussel]

Hi @ejtwe

This is definitely possible and is slightly simpler for a few things. We actually had an implementation for it some time ago, but removed for the release.

The interfaces required for this are different from the ones of a perspective-style camera. Consider a ray starting at your sensor, and that is tangential to your geometry (it's on its directly visible silhouette). In order to move to either side of the silhouette/discontinuity, you either need to move your ray origin with an orthographic sensor, or the ray direction with a perspective sensor. The required information by each senor type is different. There are also some jacobians that would also need to be changed because of this difference.

Getting this implemented nicely in a unified interface isn't straightforward. In addition, we didn't really have the time to revisit this, hence why it hasn't been done yet.