Setting up-Vector locks y-axis rotation?

Unity Engine
1

Hi there,

As far as I understood the complex relations between a directional Vector3 like transform.up, a Vector3 storing euler-angles and those devilish quaternions, setting only one directional Vector only locks 2 rotation-axes.
E.g. if you set the up-vector of yourself to look skywards, you have to stand all the time on your feet, so your head points to the sky (x-axis and z-axis locked). However, you could rotate around your own y-axis as your head would still point to the sky.

That’s where my problem kicks in:
I’ve coded a script that does movement on an uneven terrain or planet, parallel to the ground.

For achieving the desired effect, I’ve did these things:

  • My character is moved forward (transform.position += transform.forward * speed * time.deltaTime)
  • A ray is casted from my character downwards (-transform.up).
  • The player is moved to the point where the ray hit the planet (transform.position = hit.point)
  • The player’s up vector is set to the normal of the point where the ray hit the planet (transform.up = hit.normal)

It works so far, however I simply can’t rotate the player on the y-axis.

Any help or ideas?

Thank you very much!

2

I’ve got a sample of the effect you may be looking for:
http://forum.unity3d.com/threads/72665-Planetary-Gravity
Look for Ntero near the bottom. It’s VERY basic and ugly(a few hours of testing and tinkering), but it shows how to handle directional gravity, it’s on a Sphere but the code works easily as well on a tetrahedron or a cube.

Using the Cross Product or Lookat allows you to get to axis, and therefore specify a full rotation, whereas setting up will just specify a plane and can potentially get all wonky as an arbitrary rotation is chosen.

3

Thank you Ntero, I’ll check your link :slight_smile:

4

Yay, I’ve finally found a solution on my own.
@Ntero: Your code is not exactly what I need unfortunately.

Here’s my solution:

Setting the up-vector to the normal of the poly my object stands on locks all axes, this seems inevitable.
Hence, I employ a parent object. The parent object gets moved in the direction of the child-objects forward vector and the parent objects up vector is set to the raycast hit normal.
The rotation, though, is applied to the child object.

It works like a charm!

Thx