Why return 2 * fx when cheirality exception is met in GenericProjectionFactor?

[amaysaxena]

Hello,

In GenericProjectionFactor, we have the following handling for when camera.project throws a CheiralityException:

} catch(CheiralityException) {
         if (H1) *H1 = Matrix::Zero(2,6);
         if (H2) *H2 = Matrix::Zero(2,3);
         if (verboseCheirality_)
           // Stuff
         if (throwCheirality_)
            // Other stuff
}
return Vector2::Constant(2.0 * K_->fx());

What is the rationale behind returning (2 fx, 2 fx) as the error vector? Why is this a better choice than anything else? Would appreciate if someone could help me understand this a bit better.

[ProfFan]

I actually have the same question. This fragment of code is really old (11 years ago!) by @richardroberts . Origin is at 3d68672 . Unfortunately no explanation is given in the commit comments.

Pinging @dellaert @varunagrawal for help.