This class is used to compute a 3D bounding box enclosing objects defined by a scene graph. The box is a rectangular prism. The action also computes the center point, which is defined differently for different objects. (For example, the center of an OIV.Inventor.Nodes.SoFaceSet is the average of its vertices' coordinates.) For a group, the center point is defined as the average of the centers of all shapes in it.

Each bounding box is calculated as an OIV.Inventor.SbXfBox3f, where the transformation matrix is defined so that the bounding box can be stored in the object space of the OIV.Inventor.Nodes.SoShape. When two bounding boxes are combined by a group node, the combination is performed so as to produce the smaller object-space box. Note that this does not necessarily yield the smallest world-space-aligned box, especially in the case of few OIV.Inventor.Nodes.SoShape nodes. The application can accomodate this by using OIV.Inventor.Nodes.SoBBox nodes. The result of the calculation by the action can be returned as an OIV.Inventor.SbXfBox3f or as a world-space-aligned OIV.Inventor.SbBox3f.

To calculate the bounding box of a subgraph bounded by two paths, specify the left edge of the subgraph with OIV.Inventor.Actions.SoGetBoundingBoxAction.SetResetPath(OIV.Inventor.SoPath, System.Boolean, OIV.Inventor.Actions.SoGetBoundingBoxAction.ResetTypes), and apply the action to the path that defines the right edge of the subgraph. The accumulated bounding box and transformation will be reset when the tail of the reset path is traversed.

If the subgraph being traversed does not contain any shapes, the returned bounding box will be empty (that is, SbBox3f.isEmpty() will return true).

The OIV.Inventor.Nodes.SoBBox node can be used to specify the bounding box for a shape or portion of the scene graph. This is useful, for example, to avoid the cost of computing the bounding box of a large (or frequently changing) geometry. The OIV.Inventor.Nodes.SoBBox node can also be used to specify that a shape or portion of the scene graph should not be included in the bounding box calculation. This is useful, for example, to avoid considering screen aligned "annotation" graphics like legends.

Bounding boxes are used internally by Open Inventor to optimize rendering, picking, culling and other operations. For example, the standard viewer classes apply an OIV.Inventor.Actions.SoGetBoundingBoxAction to the scene graph when automatic adjustment of the near and far clipping planes is enabled (which is the default).

Bounding boxes are cached by some grouping nodes, primarily OIV.Inventor.Nodes.SoSeparator. When this action is applied to a scene graph, it will use the cached bounding box whenever possible. So querying the bounding box of a (relatively) static scene graph is normally very fast. Open Inventor automatically detects when bounding caches become invalid and they are re-computed the next time an OIV.Inventor.Actions.SoGetBoundingBoxAction is applied.

NOTES:

• The bounding box will only include shapes that are actually traversed. For example the bounding box will not include shapes under an OIV.Inventor.Nodes.SoSwitch with whichChild set to SO_SWITCH_NONE.

• The action does not consider the visibility of shapes that are traversed. In other words the bounding box will include shapes that are invisible because of an OIV.Inventor.Nodes.SoDrawStyle, shapes that are clipped out because of an OIV.Inventor.Nodes.SoClipPlane, etc. Use OIV.Inventor.Nodes.SoBBox if necessary to exclude shapes from the bounding box computation.

• Using the correct viewport region is critical when computing the bounding box of OIV.Inventor.Nodes.SoText2 (and a few other screen space related) nodes. However the bounding box of most shape nodes does not depend on the size of the viewport region and an approximate value may be passed to the constructor.

Sets: OIV.Inventor.Elements.SoViewportRegionElement

EXAMPLE

SoGetBoundingBoxAction gba = new SoGetBoundingBoxAction( viewer.GetViewportRegion() );
gba.Apply( root );
SbBox3f bbox = gba.GetBoundingBox();

Reference