A data compression program, which can achieve compression ratios of several hundred by making (valid) assumptions about the nature of the catalogues with which it is dealing.
If the global index has so many records per S2 source that S2GIENCODE runs out of space, the user is informed of the fact. The best solution here is to tighten the criterion by which the global index was created.
The global index can be recovered later using S2GIDECODE.
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