In bounding box annotation, is used to annotate with rectangular drawing of lines from one corner to another of the object in the image as per its shape to make it fully recognizable. 2D Bounding Box and 3D Bounding Box annotation are used to annotate the objects for machine learning and deep learning.
The main purpose to reduce the range of search for the objects features and reducing the computing resources. And apart from object detection it also helps in object classification.
