object_detection_tutorial.ipynb pretrained model "resnet50 imagenet"

[YonghangW]

thanks your work!
In the file called “object_detection_tutorial.ipynb”，exp_config = exp_factory.get_exp_config('retinanet_resnetfpn_coco') use the init_checkpoint called 'gs://cloud-tpu-checkpoints/vision-2.0/resnet50_imagenet/ckpt-28080', the weight file can be obtained through other channels if I don't download it through the goole cloud storage.