jpx_metanode::get_num_regions

Use this function to determine whether or not the node is represented by an ROI description box. If it is, the function returns the number of rectangular or elliptical regions in the ROI description box; otherwise, it returns 0. The remainder of the discussion here assumes that the function returns a value greater than 0.

If this is an intermediate node, the ROI description box is the first sub-box of an association box, and all of the node's descendants (both immediate and indirect descendants) are deemed to be associated with the set of regions described by the ROI description box. Although this is the most useful case, it can happen that the node is a leaf node, involving no association box and no descendants.