GiD_Info bounding_box

GiD_Info bounding_box ?-pmin_pmax? ?-geometry|-mesh|-post? ?-layers_off_also? ?point|line|surface|volume <entity_id>?

This command returns "x_min x_max y_min y_max z_min z_max" of the bounding box that contains the visualized model with the current settings (on layers) of preprocess: depends on the current visualization mode: geometry or mesh.
If the extra flag-geometry, -mesh or -post is set then is used instead of the current visualization.
by default off layers are ignored, to change it can set -layers_off_also
It also could return the bounding box of a geometric entity, specified by its category and <entity_id>.

-pmin_pmax optional flag is valid since the version 17.1.3d and then return the more usual order "x_min y_min z_min x_max y_max z_max"