Java3D: rotating object in world coordinates?

Question

I've been searching all evening but can't find the information I'm looking for, or even if it's possible, which is quite distressing ;)

I'm using Java3D and can't figure out how to rotate the camera in world space.

My left/right, and up/down rotation both happen on local space. Meaning that if I move left and right, everything looks fine. However if I look 90 degrees down, then look 90 degrees right, everything appears to be on its side.

Currently, I'm doing the following. This will result in the above effects:

TransformGroup cam = universe.getViewingPlatform().getViewPlatformTransform();
Transform3D trfcam = new Transform3D();
cam.getTransform(trfcam);

trfcam.mul(Camera.GetT3D()); //Gets a Transform3D containing how far to rotate left/right and how far to move left/right/forward/back

trfcam.mul(Camera.GetRot()); //Gets a t3d containing how far to rotate up/down

cam.setTransform(trfcam);

Alternatively, one thing I tried was rotating the root, but that rotates around 0, so if I ever move the camera away from 0, it goes bad. Is there something available on the web that would talk me through how to achieve this kind of thing? I've tried a lot of different things but just can't seem to get my head around it at all. I'm familiar with the concept, as I've achieved it in Ogre3D, just not familiar with the law of the land in J3D.

Thanks in advance for replies :)

Regic Regic · Accepted Answer · 2011-04-14T11:16:15

Store the ammound you have rotated around each axis (x and y), and when you try to rotate around the x axis for example, reverse the the rotation around y, do the rotate around x, then redo the rotation around y.

I'm not sure I understand your second question correctly. Since viewer and model transformations are dual, you can simulate camera moves by transforming the world itself. If you dont want to translate the x and y axis you are rotating around, just add another TransformGroup to the main TransformGroup you are using, and do the transforms in the new one.

Edit: The first solution is quite slow, so you can make a Transform3D out of the 3 transform you have to do:

Say you have rotated around the x axis (Translate3D xrot), and now you need to rotate around y:

Translate3D yrot = new Translate3D();  
yrot.rotY(angle); 

Translate3D temp = xot; 
xrot.mul(yrot);  // Dont forget the reverse order. xrot is the previous translate 
xrot.mul(yrot);  // xrot = xrot * yrot * xrot^-1
temp.transpose();  // Get the reverse transform of the old transform
xrot.mul(temp);

yrot = xrot;  // Store it for future rotation around x axis
cam.setTransform(yrot);

It works similar for many transformations you make: reverse the previous done, do the transform, redo the old one. I hope it helps.

Java3D: rotating object in world coordinates?

1 Answers