TransformGroup

• A TransformGroup enables you to build a new coordinate system relative to a parent

  • Translate

  • Rotate

  • Scale

• Shapes built in the new coordinate system are relative to it

• If you translate the coordinate system, the shapes move too

• Transformations accumulate as the scene graph is traversed

  • This creates an overall Composite Modeling Transform (CMT)

• Transformations lower (closest to the geometry) in the scene graph appear to happen before those farther up in the scene graph

• TransformGroup extends the Group class

The TransformGroup node specifies a single spatial transformation-via a Transform3D object -that can position, orient, and scale all of its children.
The specified transformation must be affine. Further, if the TransformGroup node is used as an ancestor of a ViewPlatform node in the scene graph, then the transformation must be congruent-only rotations, translations, and uniform scales are allowed in a direct path from a Locale to a ViewPlatform node. A BadTransformException is thrown if an attempt is made to specify an illegal transform.
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Note: Even though arbitrary affine transformations are allowed, better performance will result if all matrices within a branch graph are congruent-containing only rotations, translation, and uniform scale.
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The effects of transformations in the scene graph are cumulative. The concatenation of the transformations of each TransformGroup in a direct path from the Locale to a Leaf node defines a composite model transformation (CMT) that takes points in that Leaf node's local coordinates and transforms them into Virtual World (Vworld) coordinates. This composite transformation is used to transform points, normals, and distances into Vworld coordinates. Points are transformed by the CMT. Normals are transformed by the inverse-transpose of the CMT. Distances are transformed by the scale of the CMT. In the case of a transformation containing a nonuniform scale or shear, the maximum scale value in any direction is used. This ensures, for example, that a transformed bounding sphere, which is specified as a point and a radius, continues to enclose all objects that are also transformed using a nonuniform scale.