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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (SIS-448) Extension to CF-conventions for localization grid smaller than data in netCDF
Date Sun, 17 Mar 2019 14:37:00 GMT

     [ https://issues.apache.org/jira/browse/SIS-448?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Martin Desruisseaux resolved SIS-448.
-------------------------------------
    Resolution: Fixed

> Extension to CF-conventions for localization grid smaller than data in netCDF
> -----------------------------------------------------------------------------
>
>                 Key: SIS-448
>                 URL: https://issues.apache.org/jira/browse/SIS-448
>             Project: Spatial Information Systems
>          Issue Type: Improvement
>          Components: Storage
>            Reporter: Martin Desruisseaux
>            Assignee: Martin Desruisseaux
>            Priority: Major
>             Fix For: 1.0
>
>
> The _Global Change Observation Mission - Climate (GCOM-C)_ data have content like below
(simplified):
> {noformat}
> group: Geometry_data {
>     variables:
>         float Latitude(161, 126)
>         string Unit = "degree"
>         string Dim0 = "Line grids"
>         string Dim1 = "Pixel grids"
>         int Resampling_interval = 10
>     float Longitude(161, 126)
>         string Unit = "degree"
>         string Dim0 = "Line grids"
>         string Dim1 = "Pixel grids"
>         int Resampling_interval = 10
> }
> group: Image_data {
>     variables:
>         ushort SST(1599, 1250)        // Note: different size than (latitude, longitude)
variables.
>         string dim0 = "Line grids"
>         string dim1 = "Pixel grids"
>         string Unit = "degree"
> }
> {noformat}
> The size of latitude and longitude variables is not the same than the size of image data.
In this case, even if reader correctly identifies {{Latitude}} and {{Longitude}} as the variables
to use for building a localization grid, we are still unable to associate the {{SST}} variable
to those axes because they have no dimension in common. However if we interpret {{dim0}} and
{{dim1}} attributes as _"Name of dimension 0"_ and _"Name of dimension 1"_ respectively, then
we can associate the same dimension *names* to all those variables: namely {{"Line grids"}}
and {"Pixel grids"}} in above example. Using those names, we deduce that the ({{data_y}},
{{data_x}}) dimensions in the {{SST}} variable are mapped to the ({{grid_y}}, {{grid_x}})
dimensions in the localization grid.
> The feature is an extension to CF-conventions, as I'm not aware of equivalent mechanism
in CF at this time. The {{coordinates}} attributes is not exactly the same since it tells
us which variable to use, but not which dimensions (an ambiguity still exists if the variable
has 2 or more dimensions).



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