Question by pappapierre · Jan 30, 2013 at 01:40 PM · camera rotation quaternion axis sphere

"Free" rotation about a sphere

ok, so, I need to get a camera placed on a sphere with a rolling object on the surface. I am able to get gravity, as i am actively changing gravity based on the ball position versus the planet's center.

I have a camera nested inside a couple of gameobjects, but i need the camera to always look over the horizon from behind my ball. The problem is that i can't get the camera to behave as expected every time it reaches the south pole... i'm moving forward with the ball, and then all of a sudden the camera direction inverts and we're moving backwards.

now, the real question is, how can i take this gravity vector and manipulate the camera to ignore the world-space up vector? My current solution is below, but this is exactly my problem - stumped.

transform.up = -Physics.gravity;

^ edited as to what i actually meant.. I'll post a video to show the problem the moment i have the opportunity..

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Wolfram · Jan 31, 2013 at 10:02 PM 0

The LHS is a Vector3, while the RHS is a float, this shouldn't even compile. Why not just use

 transform.up = -Physics.gravity;

MD_Reptile · Feb 01, 2013 at 12:48 AM 0

I am not totally understanding the problem @pappapierre I guess what you need is to have your camera follow your "ball" gameobject around as this ball rotates around the place (like the roll-a-ball tutorial) but this is happening while "orbiting" around a larger sphere which is like a planet?

I would offer some advice but I am not totally sure that is what you mean?

pappapierre · Feb 01, 2013 at 08:42 AM 0

the problem is that whenever my camera reaches the south pole of the "planet", the -physics.gravity vector messes with my forward direction, and the camera swivels uncontrollably.. i think it's a problem with the camera's local up, but i've found a work around in the meantime:

Using the bounding box of the object i'm following, i'm checking the apparent velocity, and using that value as a forward direction and gravity as the up direction... This does mean i have a second GameObject to worry about, but it also gives me alot more control over how the camera follows the object.

thanks for the replys though! i'll post a link to product when we're done.