John,
As a follow up to my posting of the NetCDF-Java/CF projection to
GeoTools/GeoAPI converter utility posting. As background we are doing
geoprocessing of vector geometries obtained from Shapefiles or GML (often via
WFS). Given the large number of CRS that maybe used with these vector
geometries (relative to what's available with CF) and the desire to perform the
calculations in the CRS used with the vector geometries we generate a
GeoTools/GeoAPI CRS instance so that we can transform the CF grids into the
vector geometry CRS.
An issue we have with NetCDF-Java is that not the NetCDF-Java Projection
instance isn't passing through the ellipsoid parameters for Projection
implementations that don't have transformation to ellipsoids implemented (even
though the CF spec. Ideally we could extract these from
Projection.getProjectionParameters() so that we can generate a fully
parameterized GeoAPI CoordinateReferenceSystem instance which will then use
these parameters. Given the abstraction of GridDatatype/GridCoordSystem is
very difficult to extract these parameters from the original CF grid_mapping.
Could we get these parameters (semi_major_axis, semi_minor_axis and
inverse_flattening) in the Projection instance for all Projections if they are
in the grid_mapping for the grid?
One thing i've been hoping to do is implement a ProjectionProviderFactory type
architecture for NetCDF-Java that would allow the implementation of NetCDF-Java
Projection instances using GeoTools or Geotk. One could register a factory
using a service registration mechanism then get back Projection implementations
back by their API of choice. This would remove the need for NetCDF-Java to
re-implement projection transformations that are already implemented in
GeoTools or Geotk. The CRSUtility class I provided earlier could be the
foundation/crosswalk for a GeoToolsProjectionProviderFactory. One can easily
generate transforms and their inverses once the CoordinateReferenceSystem
instance is generated. These transforms can the be wrapped in a NetCDF-Java
Projection instance This would also allow CF to incorporate new projections
and minimize implementation time in NetCDF-Java.
Tom Kunicki
Center for Integrated Data Analytics
U.S. Geological Survey
8505 Research Way
Middleton, WI 53562
