# Negative tilt and retaining heading & roll at vertical tilt

Why camera heading and roll should both be retained

Lets say someone starts off at heading 45, pitch -89, roll 45. Now they want to only alter their world pitch to -90 and nothing else. That means that heading is still 45 and roll is still 45. Is that the same orientation (DRU-DirRightUp) as heading 90, pitch -90, roll 0? Ya, but so what?

Now they want to only alter their world pitch say to 0 and nothing else. Well if their heading and roll information wasn’t lost they’d be at heading 45, pitch 0, roll 45. If any of this info was lost they might instead end up at heading 90, pitch 0, roll 0. They might be upset about this.

So if a program only saves DRU vectors you lose heading and roll information at vertical pitch. So it’s best to save heading and roll, so when you perform a ‘world pitch movement’ you retain the proper heading and roll.

At vertical pitch ‘up vector heading’ = sum of heading and roll

Example: (45H, -89.99P, 45R) is the basically the same view as (90H, -89.99P, 0.0R)

So at -90P the ‘up vector heading’ is the sum of heading and roll angles. There is no ‘direction vector heading’ at vertical pitch.

Something I call hemiflip (for lack of a better term)

Google Earth used to let you do this, but they’ve seem to have disabled it recently. Let’s say someone starts with heading 0, pitch 0, roll 0. Then they change only their pitch to -90 and retain heading 0 roll 0.

Now lets say they want to ‘world pitch’ in a negative direction, basically to a ‘negative tilt’ value.

With a negative tilt: