World versus Local Axes

When manipulating objects in Unity, it appears that the axes gizmos are only available in local coordinates. Is there a way that I translate and rotate objects in Unity using a world axes gizmo?

If not, this would definitely be a nice future feature to consider.

 

Could you folks please provide a simple code example showing how to rotate and translate an object along it's own X, Y or Z?

One line of code for each would be fine - I just need to see the line of code that does the local transform change.

Thanks!

 

This should work... of course if you rotate like this, the order of the rotations matters, and can get you into funny positions... but any one of the following will work nicely.

First take a direction, and use TransformDirection() figure out what it is in world-space, than rotate around or translate along that direction.

3D maths aren't really complicated, but take a little getting used to. At the end of the GooBall production you can image we got quick doing it ("now, with the ball stuck on the side of this wall, what direction should it move when I press 'left'?")

Note: The multiplication with Time.deltaTime is to get an even movement regardless of the framerate which effects how often Update() is called...

Code (csharp):

1.  
2. var angleX = 45.0;
3. var angleY = 45.0;
4. var angleZ = 45.0;
5. var translateX = 1.0;
6. var translateY = 1.0;
7. var translateZ = 1.0;
8.  
9. function Update() {
10.   transform.RotateAround(transform.TransformDirection(Vector3.right), angleX * Mathf.Deg2Rad * Time.deltaTime);
11.   transform.RotateAround(transform.TransformDirection(Vector3.up), angleY * Mathf.Deg2Rad * Time.deltaTime);
12.   transform.RotateAround(transform.TransformDirection(Vector3.fwd), angleZ * Mathf.Deg2Rad * Time.deltaTime);
13.  
14.   transform.position += transform.TransformDirection(Vector3.right) * translateX * Time.deltaTime;
15.   transform.position += transform.TransformDirection(Vector3.up) * translateY * Time.deltaTime;
16.   transform.position += transform.TransformDirection(Vector3.right) * translateZ * Time.deltaTime;
17. }
18.  

 

Yippee! Works like a charm, David! Thanks for the feedback and code!

I'm curious though, why isn't there a simpler way to move or rotate an object on it's local axes in Unity? In other 3D authoring applications and API's I've used, I don't need to do any math to do simple local-axis transforms.

 

That's what the transform property is for. Every GameObject has a transform property, which represents the object's position in the game world.

That's why you call methods on and generally manipulate the transform when you want to do something to the object's position, orientation or scale.

 

Right, but Unity's transform property seems to require a little math to do rotation on a local axis. It's no biggie (now that I've been shown the light - thanks again, David), but I'm just wondering why there couldn't be a command that explicitly does local-axis rotation, without the need to do any math.

For anyone following this thread, David's post above works like a charm.

 

That's true. Either world-space coordinates through transform.position (and ditto for transform.rotation) or parent-relative coordinates through transform.localPosition (plus localRotation and localScale)
Note the local versions are relative to the parent object's local axes and not the object itself. (Hint: it can often be useful to position a game object inside an otherwise invisible parent game object in the scene)

You can use the transform component's TransformDirection to transform an object-local direction to global space:

Code (csharp):

1.  
2. localUpAxis = transform.TransformDirection(Vector3.up);
3.  

... and then use it with RotateAround to rotate the object:

Code (csharp):

1.  
2. transform.RotateAround(localUpAxis, angle_in_radians);
3.  

 

Still not working.

 

Actually, the following seems to work fine for local rotation:

transform.RotateAround(transform.TransformDirection(Vector3.up), y);

... where y is the units to turn.

Is this just a longhand version of the RotateAroundLocal function?

 

I'm having trouble with the following not translating on a local all of the time as well:

transform.position += transform.TransformDirection(Vector3.right) * x;

Any idea what might cause that?

I'm curious, why is there no TranslateLocal method?

 

Hmm... It seems the ...Local functions need some rethinking. We'll revamp these, so if you use them, there might be some small code changes on your side required in 1.0.1

 

I'm used to using raw OpenGL, where you have to multiply the transformation matrices together in a particular order (the multiplication not being commutative and all that...) So that's how I'm accustomed to thinking about 3d transforms.

So, in the "Translation" component, what order are the parts being applied in? Is it Tranlate, Rotate, Scale? Maybe it would be possible to have several transforms, or to be able to change the order?

For example, (this might be flawed for this discussion or not make sense, since it's based on "re-drawing" a sphere every frame, instead of having "GameObject") if you rotate a cube 45 degrees, then translate it 10 unites out, and translate another cube 10 units, THEN rotate it 45 degrees, the two cubes will have all faces parallel to each other, but will have a 45 degree arc between them.

That's the main issue I have with the way Unity's translation component works currently. Am I rambling? Does that make any sense? Would something slightly different be more useful? Am I the only one who cares?

 

The Transform scripting interface has been revamped since this forum thread was active.

Please take a look at the documentation at
http://otee.dk/Documentation/ScriptReference/Transform.html

 

Got it, sad thing is I was actually looking at the new documentation last night when I started wondering about this stuff. Though, how should this kind of thing be dealt with in terms of scene setup? Looking at the component inspector for the transform still just has the 9 fields, without any indication of order, etc. Is that set to change?

 

Not for the time being. What you can do is use hierachies to achieve what you want.

We try to keep Unity simple without taking away power: this seems a good method to get that.

Don't hesitate to ask for help if you have specific problems with it: I'm sure you will get help to make your projects work.

 

Working with an object hierarchy is actually what sent me looking for these other joint types to begin with.

What I was trying to do is make a replicate-able 'car' type object, with objects like so:

Car
óChassis
óLeftWheel
óRightWheel
óetc.

Where chassises, wheels, et al. are all rigid bodies, connected as expected with Hinge joints. When I hit run, the Chassis and attached wheels, etc, fall to the ground, and continue on together. However, the "Car" object sits still. If I make "Car" also a rigid body, it ends up falling through the ground, and taking the rest of the car with it. It seems like it did this even with the "Kinematic" flag set. (Sorry, I don't have Unity in front of me ATM.) But everything seems to not work.

What is the correct setup of relationships between these objects?

 

Is this still the "official" workaround for Unity iPhone 1.7 and 3.0? Thanks, Ben