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<html><head><title>DODS -- OPeNDAP Grid Client</title></head><body bgcolor="#ffffff"><h1>DODS -- OPeNDAP Grid Client</h1>GDAL optionally includes read support for 2D grids and arrays via the OPeNDAP(DODS) protocol. <p><h2>Dataset Naming</h2>The full dataset name specification consists of the OPeNDAP dataseturl, the full path to the desired array or grid variable, and an indicatorof the array indices to be accessed.<p>For instance, if the url http://maps.gdal.org/daac-bin/nph-hdf/3B42.HDF.dds returns a DDS definition like this:<p><pre>Dataset { Structure { Structure { Float64 percipitate[scan = 5][longitude = 360][latitude = 80]; Float64 relError[scan = 5][longitude = 360][latitude = 80]; } PlanetaryGrid; } DATA_GRANULE;} 3B42.HDF;</pre><p>then the percipitate grid can be accessed using the following GDAL dataset name:<p>http://maps.gdal.org/daac-bin/nph-hdf/3B42.HDF?DATA_GRANULE.PlanetaryGrid.percipitate[0][x][y]<p>The full path to the grid or array to be accessed needs to be specified (notcounting 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.<p>In cases of data servers with only 2D arrays and grids as immediatechildren of the Dataset it may not be necessary to name the grid or arrayvariable. <p>In cases where there are a number of 2D arrays or grids at the datasetlevel, they may be each automatically treated as seperate bands.<p><h2>Specialized AIS/DAS Metadata</h2>A variety of information will be transported via the DAS describingthe dataset. Some DODS drivers (such as the GDAL based one!) alreadyreturn the following DAS information, but in other cases it can besupplied locally using the AIX mechanism. See the DODS documentationfor details of how the AIS mechanism works. <p><pre>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 "..."; String }}</pre><h3>Dataset</h3>There will be an object in the DAS named GLOBAL containingattributes of the dataset as a whole. <p>It will have the following subitems:<p><ul><li> <b>Northernmost_Northing</b>: The latitude or northing of the north edge of the image. <p><li> <b>Southernmost_Northing</b>: The latitude or northing of the south edge of the image. <p><li> <b>Easternmost_Easting</b>: The longitude or easting of the east edge of the image. <p><li> <b>Westernmost_Easting</b>: The longitude or easting of the west edge of the image.<p><li> <b>GeoTransform</b>: The six parameters defining the affine transformationbetween pixel/line space and georeferenced space if applicable. Storedas a single string with values seperated by sapces. Note this allows for rotated or sheared images. (optional) <p><li> <b>SpatialRef</b>: The OpenGIS WKT description of the coordinate system.If not provided it will be assumed that the coordinate system is WGS84.(optional) <p><li> <b>Metadata</b>: a container with a list of string attributes foreach available metadata item. The metadata item keyword name will be usedas the attribute name. Metadata values will always be strings. (optional)<li> <i>address GCPs</i><p></ul>Note that the edge northing and easting values can be computed basedon the grid size and the geotransform. They are included primarily asextra documentation that is easier to interprete by a user than theGeoTransform. They will also be used to compute a GeoTransform internallyif one is note provided, but if both are provided the GeoTransform willtake precidence.<p><h3>Band</h3>There will be an object in the DAS named after each band containingattribute of the specific band. <p>It will have the following subitems:<p><ul><li> <b>Metadata</b>: a container with a list of string attributes foreach available metadata item. The metadata item keyword name will be usedas the attribute name. Metadata values will always be strings. (optional)<p><li> <b>PhotometricInterpretation</b>: Will have a string value that isone of "Undefined", "GrayIndex", "PaletteIndex", "Red", "Green","Blue", "Alpha", "Hue", "Saturation", "Lightness", "Cyan", "Magenta","Yellow" or "Black". (optional)<p><li> <b>units</b>: name of units (one of "ft" or "m" for elevation data).(optional)<p><li> <b>add_offset</b>: Offset to be applied to pixel values (after scale_factor) to compute a "real" pixel value. Defaults to 0.0. (optional)<p><li> <b>scale_factor</b>: Scale to be applied to pixel values (beforeadd_offset) to compute "real" pixel value. Defaults to 1.0. (optional)<p><li> <b>Description</b>: Descriptive text about the band. (optional)<p><li> <b>missing_value</b>: The nodata value for the raster. (optional)<p><li> <b>Colormap</b>: A container with a subcontainer for each color inthe color table, looking like the following. The alpha component isoptional and assumed to be 255 (opaque) if not provided.<p><pre> Colormap { Color_0 { Byte red 0; Byte green 0; Byte blue 0; Byte alpha 255; } Color_1 { Byte red 255; Byte green 255; Byte blue 255; Byte alpha 255; } ... }</pre></ul><hr>See Also:<p><ul><li> <a href="http://www.opendap.org/">OPeNDAP Website</a></ul></body></html>⌨️ 快捷键说明
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