sahrk / DGGRID

A command-line application that generates and manipulates icosahedral discrete global grids.
GNU Affero General Public License v3.0
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Clarification about address types: How are cells ordered in the index? #69

Open danlooo opened 1 year ago

danlooo commented 1 year ago

Thanks a lot for updating DGGRID with new address types for indexing cells! The order of the cells matter a lot when it comes to chunking the data so that geographically nearby cells are stored and compressed in the same chunk. However, I still try to understand how the cells are ordered according to the various indexing methods:

  1. How are SEQNUM values in ISEA actually being calculated? Is there a specific way to iterate over the cells in each icosahedral face? Is SEQNUM like a linear version of PROJTRI?

  2. ZORDER refers to Morton space-filling curves aka, Lebesgue curve, right?

  3. What exactly is Z3? Does it relate to this Z3 index?

  4. SUPERFUND uses hierarchical Central Place Indexing (CPI) as described in (Sahr, 2011; Sahr, 2019). I think this index is well documented in the manual.

allixender commented 1 year ago

Hi @danlooo , DGGRID has been updated again and the manual has been updated as well. @sahrk will know better, but I think seqnums are globally stable when the DGGS is instantiated with same parameters, but I am not sure how they are calculated/generated. I think it depends on the internal data structure how cells are created and then its just a linear enumeration.