class list
class_names = ['bg','worker_helmet','worker_nohelmet','rebar_working','rebar_material',
'steel','concrete_pouring','formwork_working','formwork_material','scaffolding',
'excavator','bulldozer','dump_truck','concrete_bucket','concrete_mixer',
'concrete_pump','tower_crane','crane','machine_other',
'pile','container','concrete_mixing_station','construction_base','beam','pile_cap']
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