Yi-Chia Chang

#1840 is adding [South Africa Crop Type Competition](https://mlhub.earth/data/ref_south_africa_crops_competition_v1)

That's all I want to add to this PR. Thanks for reviewing the code, @adamjstewart!

If we change the split portion from [0.8, 0.1, 0.1] to something like [0.6, 0.2, 0.2], we can reduce 50% of test images. `random_bbox_assignment(self.dataset, [0.8, 0.1, 0.1], generator=generator)` For the...

I think it is still better to include this change. If we can reduce the number of test files, it would be great to have `RandomGeoSampler` for pre-chipped datasets.

I lean to option 1. This PR could be closed.

I cannot reproduce the issue either. The dataset can be downloaded immediately. I did find that the other years can't be downloaded after downloading some years. For example: ``` from...