Coverage Dataset

Overview

Coverage Datasets are collections of Coverage Features such as Grid, Fmrc, and Swath. FeatureDatasetCoverage are containers for CoverageCollections:

public class ucar.nc2.ft.FeatureDatasetCoverage extends ucar.nc2.ft.FeatureDataset, Closeable {
  public List<CoverageCollection> getCoverageCollections();
  public CoverageCollection findCoverageDataset( FeatureType type);
  public ucar.nc2.constants.FeatureType getFeatureType();
}

FeatureDatasetCoverage extends FeatureDataset, and contains discovery metadata for search and discovery. A CoverageCollection can only have a single HorizCoordSys, Calendar, and FeatureType. A single endpoint (eg GRIB collection) often has more than one HorizCoordSys or Type (eg Best and TwoD), and so has multiple collections. When there are multiple types, getFeatureType() returns the generic FeatureType.COVERAGE. Otherwise it will return the specific type.

  • Grid: all coordinates are one dimensional, aka seperable.
  • Fmrc: Both a runtime and time coordinate exist. The time coordinate may be 2D, or it may be a 1D time offset coordinate.
  • Swath: has 2D lat/lon & time exists but not independent
  • Curvilinear: has 2D lat/lon & time independent if it exists

A Coverage Collection contains coverages, coordinate systems, coordinate axes, and coordinate transforms. All of the coverages in a collections are on the same horizontal grid, and have the same datetime Calendar.

public class CoverageCollection implements Closeable {
  public String getName();
  public FeatureType getCoverageType();

  public List<Attribute> getGlobalAttributes();
  public String findAttValueIgnoreCase(String attName, String defaultValue);
  public Attribute findAttribute(String attName);
  public Attribute findAttributeIgnoreCase(String attName);

  public LatLonRect getBoundingBox() ;
  public ProjectionRect getProjBoundingBox();
  public CalendarDateRange getCalendarDateRange();
  public ucar.nc2.time.Calendar getCalendar();

  public List<CoordSysSet> getCoverageSets();
  public List<CoverageCoordSys> getCoordSys();
  public List<CoverageTransform> getCoordTransforms();
  public List<CoverageCoordAxis> getCoordAxes();
  public CoverageCoordSys findCoordSys(String name);
  public CoverageCoordAxis findCoordAxis(String name);
  public CoverageTransform findCoordTransform(String name);
  public HorizCoordSys getHorizCoordSys();

  public Iterable<Coverage> getCoverages();
  public int getCoverageCount();
  public Coverage findCoverageByAttribute(String attName, String attValue);

  public void close()
}

CoordSysSet

A CoordSysSet simply groups all of the Coverages that belong to the same CoverageCoordSys:

public class CoordSysSet {
  public CoverageCoordSys getCoordSys();
  public List<Coverage> getCoverages();
}

CoverageCoordSys

Coverage Coordinate Systems

A CoverageCoordSys represents the Coordinate System for Coverages.

public class CoverageCoordSys {
  public String getName();
  public FeatureType getCoverageType();

  public List<String> getAxisNames();
  public List<CoverageCoordAxis> getAxes();
  public CoverageCoordAxis getAxis(String axisName);
  public CoverageCoordAxis getAxis(AxisType type);
  public CoverageCoordAxis getXAxis();
  public CoverageCoordAxis getYAxis() ;
  public CoverageCoordAxis getZAxis();
  public CoverageCoordAxis getTimeAxis();

  public List<String> getTransformNames();
  public List<CoverageTransform> getTransforms();
  public CoverageTransform getHorizTransform();
  public HorizCoordSys getHorizCoordSys();

  public boolean isRegularSpatial();
  public ProjectionImpl getProjection();
}

CoverageCoordAxis

public class CoverageCoordAxis {
  public String getName();
  public DataType getDataType();
  public AxisType getAxisType();
  public List<Attribute> getAttributes();
  public String getUnits();
  public String getDescription();

  public int getNcoords();
  public DependenceType getDependenceType();
  public Spacing getSpacing();
  public double getResolution();
  public double getStartValue();
  public double getEndValue();

  public boolean isRegular();
  public boolean isScalar();
}

public enum DependenceType {
  independent,             // has its own dimension, is a coordinate variable, eg x(x)
  dependent,               // aux coordinate, eg reftime(time) or time_bounds(time);
  scalar,                  // eg reftime
  twoD                     // eg time(reftime, time), lat(x,y)
}

public enum Spacing {
  regular,           // regularly spaced points or intervals (start, end, npts),
                     // edges halfway between coords
  irregularPoint,    // irregular spaced points (values, npts), edges halfway between coords
  contiguousInterval,// irregular contiguous spaced intervals (values, npts),
                     // values are the edges, and there are npts+1, coord halfway between edges
  discontiguousInterval // irregular discontiguous spaced intervals (values, npts),
                     // values are the edges, and there are 2_npts: low0, high0, low1, high1..
}

CoverageTransform

A CoverageTransform contains parameters for horizontal or vertical transforms.

public class CoverageTransform  {
  public String getName();
  public boolean isHoriz();
  public ProjectionImpl getProjection();

  public java.util.List<Attribute> getAttributes();
  public Attribute findAttribute(String name);
  public Attribute findAttributeIgnoreCase(String name);
  public String findAttValueIgnoreCase(String attName, String defaultValue);
}

Classification

  • must have lat/lon or have x,y and projection
  • x and y both have rank <= 2
  • x and y both have size > 1; eliminates some miscoded point data
  • x and y have at least 2 dimensions between them (eliminates point data)
  • A runtime axis must be scalar or one-dimensional
  • Time may be 0, 1 or 2 dimensional
  • If time is 2D and runtime exists, first time dimension must agree with runtime
  • other coordinates, dependent or independent (ie has another dimension) are ok.