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""" NASA EOS mission specific data
References:
1. MODIS Command, Telemetry, Science and Engineering Description,
Document Number 151840, May 1997, Appendix C
https://directreadout.sci.gsfc.nasa.gov/documents/satellite_gen/MODIS_UG.pdf
"""
import struct
packet_types = {
0: "day",
1: "night",
2: "eng1",
4: "eng2",
}
packet_sources = {
0: "solar-diff",
1: "srca-cal",
2: "bb-cal",
3: "space-cal",
}
packets_per_scan = {
"day": 3032,
"night": 326,
}
def sourceid(p):
if p.data[0] >> 7 == 0:
return "earthdata"
return packet_sources[p.data[0] >> 5 & 0x3]
def mirrorside(p):
return ["side1", "side2"][bytes(p.secondary_header)[8] & 0x1]
def scancount(p):
return bytes(p.secondary_header)[8] >> 1 & 0x7
def pkttype(p):
return packet_types[bytes(p.secondary_header)[8] >> 4 & 0x7]
def frame_count(p):
x = int.from_bytes(b'\x00\x00' + p.data[:2], 'big')
if sourceid(p) == "earthdata":
return x >> 4 & 0x7ff
return x >> 4 & 0x3f
# Combination of source ids and packet types to their position within a scan.
_sort_indexes = {
"solar-diff": 1,
"srca-cal": 2,
"bb-cal": 3,
"space-cal": 4,
"earthdata": 5,
"eng1": 6,
"eng2": 7,
}
def _modis_sort_key(p):
""" Return a tuple that will maintain order for this packet in a stream of
MODIS data. Intended to be used as a key func for sorting.
Packets are sorted in the order defined in _sort_indexes.
"""
type_idx = _sort_indexes.get(pkttype(p), _sort_indexes[sourceid(p)])
return (p.stamp, 64, type_idx, frame_count(p), int(p.is_last()))
def sort_modis(packets):
return sorted(packets, key=_sort_key)