Issue in readme: relation with nadir & incidence angles

[louis-olivier-geosys]

Hi,

I was struggling with the following paragraph:
"The off-nadir angle and the incidence angle are related. When the off-nadir angle is low (high incidence angle) then the two angles sum to about 90, so one can be calculated from the other. However, at high off-nadir angles with high altitude sensors the curvature of the earth has an impact and their sum will be less than 90. If only providing one of the two angles, the off-nadir angle is preferred.".
From my understanding and researches, the off-nadir represents the angle from the satellite point of view and the normal, and the incidence_angle represents the one form the observed pixel and the normal.
Meaning, both are quite similar, especially when the altitude is low as the surface of the Earth could be considered flat, and slightly different when the curvature of the Earth is more impacting.
Meaning, not the sum of both is nearby 90, but the difference of both is nearby 0.
I am get wrong, but everything I can find on Internet get me to this conclusion.
I think there is just a misunderstanding between this relation, and the zenith & elevation relation (which is : "sum of zenith and elevation gives 90).

Doc: https://ww2.mathworks.cn/help/radar/ug/spaceborne-synthetic-aperture-radar-performance-prediction.html

Cheers,