Concerning the definition of a "footprint"
Say a spacecraft flying overhead of planet is pointing its camera rectangular shaped FOV down at the surface. If 1 or more of the 4 corner boundary rays stops intercepting with the surface, is the area under the FOV still considered a "footprint"? Perhaps it only matters if the borsight ray of the FOV intercepts with the planet to qualify as a "footprint" ?
I tend to think all of those 4 cornors rays would have to be intecepting the surface to qualify as a "footprint" but
I just wanted some clarification maybe from an expert.

Thank you.

Corners not necessarily define the footprint of a sensor. A camera lens distorts the field of view even when pointed perpendicular to a surface. A fish-eye lens is obviously an extreme of this, but even carefully designed lens have the same problem. Then consider that not every observation is done nadir to the surface, so the footprint can vary in shape quite considerably. The projection of the sensor onto the surface depends on the surface as well. Then you have sensors like CRISM that swing across track giving a butterfly wings footprint.

Paolo

Thank you Paolo

If an image contains the entire target planet, then none of the four corners intersect the planet, and if the planet were off-center, the boresight might not intersect the planet either, but the footprint would still be the entire visible part of the planet.

Edited topic title for clarity.