opbbox.rst

Compute bounding box

Primal's bounding boxes are rectangular right prisms. That is, they are boxes where neighboring walls are at right angles.

The BoundingBox class represents an axis-aligned bounding box, which has two walls perpendicular to the X-axis, two perpendicular to the Y-axis, and two perpendicular to the Z-axis. This is sufficient for many computations; range and intersection operations tend to be fast.

The OrientedBoundingBox class can be oriented in any way with respect to the coordinate axes. This can provide a tighter fit to the bounded data, but construction, intersection, and range calculation are more costly.

Here a group of points is used to create both an (axis-aligned) BoundingBox and an OrientedBoundingBox. The points are drawn in blue, the BoundingBox in black, and the OrientedBoundingBox in orange.

.. literalinclude:: ../../examples/primal_introduction.cpp
   :start-after: _bbox_header_start
   :end-before: _bbox_header_end
   :language: C++

.. literalinclude:: ../../examples/primal_introduction.cpp
   :start-after: _bbox_start
   :end-before: _bbox_end
   :language: C++

Primal also provides a merge_boxes() function to produce a bounding box that contains two input bounding boxes. This is available for client codes to use and also supports the operation of the BVHTree class.