I have a model instance of a character, and a model instance of a sword weapon. THe character has a node on his right hand so he can "carry" the sword. Right now I use this code so the sword's transform follows that of the node.

weaponModelInstance.transform.rotate(Vector3.Z, -90); // adjustment for blender coordinates
world.modelBatch.render(weaponModelInstance, world.environment);

this works, except that the model instance gets scaled to the scale of the node, which i do not want, i want the weapon to keep its scale. I've tried doing the following code to fix this but I end up getting weird (and wrong) rotations for the sword

        weaponModelInstance.transform.getTranslation(new Vector3()),
        weaponModelInstance.transform.getRotation(new Quaternion()),
        new Vector3(1, 1, 1)
weaponModelInstance.transform.rotate(Vector3.Z, -90);
world.modelBatch.render(weaponModelInstance, world.environment);

do anyone know how to properly copy the world translation and rotation from the node, but not its scale?


1 Answer 1


You will need to normalize the rotation matrix to remove its scale.

This can be done by normalizing all 3 rows of the transform basis matrix.

new btMatrix3x3(
, transform.getBasis().getRow(1).normalize()
, transform.getBasis().getRow(2).normalize()


new btMatrix3x3(
, transform.getBasis()[1].normalize()
, transform.getBasis()[2].normalize()

This new matrix contains only the rotation without scaling.

If you want to extract the scaling instead:

new btVector3(
, transform.getBasis()[1].length()
, transform.getBasis()[2].length()
  • 2
    \$\begingroup\$ Alternatively, you could use libgdx's Matrix4#getRotation(Quaternion, boolean), the boolean argument being a "normalizeRotation" flag that, when set to true, tells libgdx to perform this operation for you. \$\endgroup\$
    – Chris Bode
    May 2, 2015 at 21:11

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