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GALEON IE: data model reconciliation between netCDF
and WCS/GML
Stefano Nativi – CNR-IMAA and University of Florence (Italy)
Lorenzo Bigagli – CNR-IMAA and University of Florence (Italy)
Ben Domenico – Unidata/UCAR (USA)
John Caron – Unidata/UCAR (USA)
Outline
• Rationale
• Data models
• Reconciliation approach
• Available implementation: the ncML-GML
• Examples
Rationale• We must explicitly mediate from netCDF
hyperspatial data to WCS coverage models
netCDF dataset WCS coverage
N independent dimensions (i.e. axes) 2, 3, 4 coverage domain dimensions
Set of scalar variables Coverage range-set of values
(t, z, y, x) variable shape (x, y, z, t) domain shape
Implicit geo-location metadata Explicit geo-location metadata
Grid geometry irregularly spaced Grid geometry regularly spaced
etc. etc.
2 Dimension Coordinate System
Implicit/explicit Geometry
Range set
Spatial Reference System (SRS)
2 Dimension Coordinate System
Implicit/explicit Geometry
Range set
Spatial Reference System (SRS)
2 Dimension Coordinate System
Implicit/explicit Geometry
Range set
Spatial Reference System (SRS)
2 Dimension Coordinate System
Implicit/explicit Geometry
Range set
Spatial Reference System (SRS)
Mediation Process
netCDF hyperspacedataset(3/4/5D)
2D + elev + time Coverages
2D+elev+time dataset
2D SCS + elev + time
Implicit/explicit Geometry
Range set
Spatial Reference System (SRS)
a Coverage
0110110011111010101010010101…01101100111
11010101010010101…
N-Dimension Coordinate Systems
explicit/semi-implicit/implicit Geometry
Scalar measured quantities
Conceptual mapping
NetCDF concepts Mapping cardinality
Geo-Information concepts
Dataset 1…n Coverage
Dimension n…m Grid/Multipoint Domain, CS, CRS
Variable n…m Scalar/parametric Rangeset, Grid/Multipoint Domain, CS, CRS
Attribute n…m Any
Semantics level
Mediation process: the introduced GI concepts in brief
• A netCDF dataset origins several different coverages• Each coverage is characterized by a domain, a range-
set and is referenced by a CS/CRS• Each coverage is optionally described by a geographic
extent• Each domain is characterized by a geometry
– Supported domains: regular grid domain, irregular grid domain and multipoint domain
• Each range-set lists or points set of values associated to each domain location– Supported range-set types: scalar range-set and parametric
range-set
An Implementation already exists• The ncML-GML markup language implements the presented
reconciliation model• It is a Mediation Markup Language between ncML (netCDF Markup
Language) and GML– An extension of ncML core schema, based on GML grammar
• NcML-GML version 0.7.3– based on GML 3.1.1
• N2G version 0.8– Java API for ncML-GML ver. 0.7.3
• WCS-G– WCS 1.0 which supports ncML-GML/netCDF documents
• Subsetting (domain and range-set)– netCDF– ncML-GML 0.7.3
• WCS light client– Test client for WCS-G GGMLMLGGMLML
Example: sst.nc
• Example: sst.nc (~3Mb)– Sea Surface Temperature (float) depending on
• lon = 180 ;• lat = 170 ;• time = UNLIMITED ; // (24 currently)
– Already published on OPeNDAP server
netCDF-CF
• Unrestricted domain• Special semantics attached to dimension:
– Latitude– Longitude– Vertical– Time– Pressure (added by us)
• Scalar co-domain only• Recommended axes order
– *-T-Z-Y-X
sst.nc – netCDF-CFannotated CDL
netcdf C:/WebDocs/THREDDS/GALEON/SST.NC.test/sst-again.nc {
dimensions: lon = 180; // (has coord.var) lat = 170; // (has coord.var) time = UNLIMITED; // (24 currently) // (has coord.var) bnds = 2;
variables: double lon(lon); :standard_name = "longitude"; :long_name = "longitude"; :units = "degrees_east"; :axis = "X"; :bounds = "lon_bnds"; :original_units = "degrees_east"; double lon_bnds(lon, bnds); (continue)
CF assign special semantics to some dimensions
CF mandates the use of coordinate variables for such dimensions
Semantics is associated based on :units attribute
CF conventions support partitioning an axis in cells
Standard names are defined for common dimensions/variables
double lat(lat); :standard_name = "latitude"; :long_name = "latitude"; :units = "degrees_north"; :axis = "Y"; :bounds = "lat_bnds"; :original_units = "degrees_north"; double lat_bnds(lat, bnds); double time(time); :standard_name = "time"; :long_name = "time"; :units = "days since 2001-1-1"; :axis = "T"; :calendar = "360_day"; :bounds = "time_bnds"; :original_units = "seconds since 2001-1-1"; double time_bnds(time, bnds); (continue)
Semantics is associated based on :units attribute
Semantics is associated based on :units attribute
float tos(time, lat, lon); :standard_name = "sea_surface_temperature"; :long_name = "Sea Surface Temperature"; :units = "K"; :cell_methods = "time: mean (interval: 30 minutes)"; :_FillValue = 1.0E20; // float :missing_value = 1.0E20; // float :original_name = "sosstsst"; :original_units = "degC"; :history = " At 16:37:23 on 01/11/2005: CMOR altered the data
in the following ways: added 2.73150E+02 to yield output units;Cyclical dimension was output starting at a different lon;";
(continue)
CF conventions support the description of methods applied to obtain interval values
:title = "IPSL model output prepared for IPCC Fourth Assessment SRES A2 experiment"; :institution = "IPSL (Institut Pierre Simon Laplace, Paris, France)"; :source = "IPSL-CM4_v1 (2003) : atmosphere : LMDZ (IPSL-CM4_IPCC, 96x71x19) ;
ocean ORCA2 (ipsl_cm4_v1_8, 2x2L31); sea ice LIM (ipsl_cm4_v"; :contact = "Sebastien Denvil, [email protected]"; :project_id = "IPCC Fourth Assessment"; :table_id = "Table O1 (13 November 2004)"; :experiment_id = "SRES A2 experiment"; :realization = 1; // int :cmor_version = 0.96; // float :Conventions = "CF-1.0"; :history = "YYYY/MM/JJ: data generated; YYYY/MM/JJ+1 data transformed
At 16:37:23 on 01/11/2005, CMOR rewrote data to comply with CF standardsand IPCC Fourth Assessment requirements";
:references = "Dufresne et al, Journal of Climate, 2015, vol XX, p 136"; :comment = "Test drive";
Mandatory global attribute for CF conventions
Example: Lat-Lon-Time
Lon
Time
Lat
<GML 2D+Tscalar
coverage>
netCDF file transcoding
netCDFncML-GML
WCS
Example: 2 x Lat-Lon-Time
Lon
<GML 2D+Tcomposite coverage>
transcoding
netCDFncML-GML
WCS
Time
Lat
Lon
Time
Lat
netCDF file
Example: Pressure-Lat-Lon-Time
Lon
Time
Lat
<GML 2D+T parametriccoverage>
netCDF file
transcoding
netCDFncML-GML
WCS
P
netCDF
Example: Lat-Lon-Time + Pressure-Lat-Lon-Time
<GML 2D+T parametriccoverage>
transcoding
netCDF
WCS-G
X
Time
Y
P
X
Time
Y
netCDF file
<GML 2D+Tscalar
coverage>
ncML-GMLncML-GML
