Martin Desruisseaux created SIS-448:
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Summary: 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
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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