A lot of things! Too many to mention, honestly.
- all the light calculation revolves around it, the angle at which light bounces of every surface you see
- physics calculation, think spheres bouncing of a wall at correct angles
- is the ramp in the pic below too steep for my character to walk on?
if I make rotation from “normal” I get the rotation of the surface
Yes, here’s the normal - a vector that is perpendicular to the surface:
But there is ambiguity in it, too - you may want to include more data in the calculations.
- I want to land this helicopter down on the surface below it using just
Make Rot from Z:
Here’s what I got:
Fine, but that changed the orientation of my craft, it was pointing more to the right before.
- if I also include the orientation of the heli:
I can now land like this, taking into consideration where the heli’s nose was first, and only then looking at the surface below to derive the final rotator:
If the helicopter was upside down to start with, I would need to work even harder.