The Birth Shape operator allows you to convert scene objects into particles.
Object list: the list of input objects which will be converted into particles.
Group members: if an input object is a group head, enabling this setting will convert its constituent members into particles.
Object elements: if an input object mesh has multiple sub-elements, enabling this setting will split them into multiple particles.
Center all pivots: centers the pivots of extracted meshes.
Update Cache: click this to manually update the internal cache which holds mesh data for all input objects.
Auto update: controls whether changes to input objects will automatically update the operator’s internal mesh cache.