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NcML Aggregation vs Feature Collections. NcML functionality. Modify the objects found in CDM files Especially Attributes Don’t have to rewrite the files, esp on the server Make modest changes “by hand” Alternative to ncgen , ncdump CDL in XML Aggregations

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ncml functionality
NcML functionality
  • Modify the objects found in CDM files
    • Especially Attributes
    • Don’t have to rewrite the files, esp on the server
    • Make modest changes “by hand”
  • Alternative to ncgen, ncdump
    • CDL in XML
  • Aggregations
    • Creating logical datasets out of file collections
ncml aggregations
NcML Aggregations
  • union
    • Logical union of objects inside multiple files
  • joinNew
    • Each file contains one slice – add new dimension
  • joinExisting
    • Concat existing multidim arrays together
  • tiled (never released)
    • Stitch horizontal tiles together
  • FMRC (deprecated as of 4.2)
ncml aggregations1
NcML Aggregations
  • Syntactic aggregation
    • Manipulating multidimensional arrays
    • Doesn’t know what the data means
  • High homogeneity requirements
    • Files must be identical, except for certain things
    • Difficult for Users to understand or to track
  • Assemble at runtime
    • Inefficient for large collections
    • Caching strategies cause trouble for dynamic datasets
feature collections
Feature Collections
  • Feature Types
    • Coverage: grid, swath, FMRC, ugrid*, image*
    • Discrete: point, station, profile, etc
    • Radial
  • Understands more of the dataset semantics
    • Mostly about the coordinate systems
  • Can “do the right thing” without user
    • Handle more inhomogeneity in the files

* Coming soon

slide6

Application

Scientific Feature Types

Datatype Adapter

NetCDF-Java/

CDM architecture

NetcdfDataset

CoordSystem Builder

NetcdfFile

THREDDS

I/O service provider

Catalog.xml

OPeNDAP

NetCDF-3

NIDS

NetCDF-4

GRIB

NcML

HDF5

GINI

Nexrad

DMSP

what do you need to know
What do you need to know?
  • NcML aggregation works and is stable code
    • Must know how your collection of files varies
    • Use it for simple cases
  • Feature Collections are still work in progress
    • Much easier to work with
    • All future development is here
    • You have our attention
    • Details tommorrow
  • If you have GRIB files
    • You want to use GRIB feature collections (4.3)