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opengeospatial / CRS-Gridded-Geodetic-data-eXchange-Format

Gridded Geodetic data eXchange Format
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Terminology - group. #31

Closed ccrook closed 2 years ago

ccrook commented 2 years ago

This issue is to capture some discussion around the best terminology in GGXF. The use of "group" for the second level header in the GGXF file (ie file/group/grid) is conflicting with established use in the definition and APIs of NetCDF4. In particular the current POC implementation uses a NetCDF group for both GGXF groups and GGXF grids.

A number of other options have been suggested -

From Roger: collection ggxfGroup dataGroup gridGroup gridSet dataset

From Chris: component(!) submodel dataset

In considering this I think it is worth remembering that while a group may contain many grids they are typically nested grids, and are logically a single large dense grid which is broken into a nested structure with different resolutions as a storage/computation efficiency.

kevinmkelly commented 2 years ago

My choices, in order of preference, are:

gridGroup gridSet ggxfGroup

The first two define what's in the group and the third distinguishes a NetCDF group from a GGXF group but provides no other clues as to what's in the group. Any of these work for me though.

ccrook commented 2 years ago

@kevinmkelly Of these options I prefer the last. I don't like gridGroup and gridSet!

The main reason is that I feel the attribute name shouldn't describe what is in the attribute, but rather what the role of the data in the attribute is. To me calling it gridSet is a bit like using "string" instead of "filename". I know it is a string, I can see that. What the attribute name tells me is what the string represents.

So in this case I can see the ggxf group contains grids, but why are they in this group, why is there more than one group.

Another reason is that the ggxf group can contain more information than just grids. In particular (actually possibly the only case!) in the deformation model it also contains a time function.

Of course this is difficult as a) most GGXF files only have one group and often only one grid, and b) the reason for dividing into groups may be different for different GGXF types. So all the names we have come up with are very generic - that's why it is hard I guess!

ccrook commented 2 years ago

Resolve in 28 Feb 2022 meeting - GGXF will use the term ggxfGroup in the specification.

RogerLott commented 2 years ago

Specification v0.91 (Issue #34) updated to ggxfGroup.