this correctly detects 10bpp and 1023 sentinel
still would like confirmation that this data even has a sentinel

tried it->data->bits_per_pixel (always 16)
and deriving from max count value
still need to figure out how to decide between 1023 and 16383 reliably.

note that PUG positive-northward y angles appear correct in McIDAS-V

PUG expectation is that positive y angles are north of equator
If this is not correct for Japan sector, look at reversing y array instead of negating sf/ao

Conventions, cdm_data_type, remove deprecated _Coordinate*