DODS -- OPeNDAP Grid Client

GDAL optionally includes read support for 2D grids and arrays via the OPeNDAP (DODS) protocol.

Dataset Naming

The full dataset name specification consists of the OPeNDAP dataset url, the full path to the desired array or grid variable, and an indicator of the array indices to be accessed.

For instance, if the url returns a DDS definition like this:

Dataset {
  Structure {
    Structure {
      Float64 percipitate[scan = 5][longitude = 360][latitude = 80];
      Float64 relError[scan = 5][longitude = 360][latitude = 80];
    } PlanetaryGrid;
} 3B42.HDF;

then the percipitate grid can be accessed using the following GDAL dataset name:[0][x][y]

The full path to the grid or array to be accessed needs to be specified (not counting the outer Dataset name). GDAL needs to know which indices of the array to treat as x (longitude or easting) and y (latitude or northing). Any other dimensions need to be restricted to a single value.

In cases of data servers with only 2D arrays and grids as immediate children of the Dataset it may not be necessary to name the grid or array variable.

In cases where there are a number of 2D arrays or grids at the dataset level, they may be each automatically treated as seperate bands.

Specialized AIS/DAS Metadata

A variety of information will be transported via the DAS describing the dataset. Some DODS drivers (such as the GDAL based one!) already return the following DAS information, but in other cases it can be supplied locally using the AIX mechanism. See the DODS documentation for details of how the AIS mechanism works.

Attributes {

    GLOBAL { 
        Float64 Northernmost_Northing 71.1722;
	Float64 Southernmost_Northing  4.8278;
	Float64	Easternmost_Easting  -27.8897;
	Float64	Westernmost_Easting -112.11;
        Float64 GeoTransform "71.1722 0.001 0.0 -112.11 0.0 -0.001";
	String spatial_ref "GEOGCS[\"WGS 84\",DATUM[\"WGS_1984\",SPHEROID[\"WGS 84\",6378137,298.257223563]],PRIMEM[\"Greenwich\",0],UNIT[\"degree\",0.0174532925199433]]";
        Metadata { 
          String TIFFTAG_XRESOLUTION "400";
          String TIFFTAG_YRESOLUTION "400";
          String TIFFTAG_RESOLUTIONUNIT "2 (pixels/inch)";

    band_1 {
        String Description "...";


There will be an object in the DAS named GLOBAL containing attributes of the dataset as a whole.

It will have the following subitems:

Note that the edge northing and easting values can be computed based on the grid size and the geotransform. They are included primarily as extra documentation that is easier to interprete by a user than the GeoTransform. They will also be used to compute a GeoTransform internally if one is note provided, but if both are provided the GeoTransform will take precidence.


There will be an object in the DAS named after each band containing attribute of the specific band.

It will have the following subitems:

See Also: