Geolocating HDF-EOS Data

A primary function of the HDF-EOS format is to specify geolocation information in a file. Each HDF-EOS object (point, swath, or grid) supports geolocation differently. Point and swath files provide explicit latitude and longitude values. For grid structures, the HDF-EOS library uses the U.S. Geological Survey (USGS) General Cartographic Transformation Package (GCTP) conventions for storing projection information. Tools that fully support HDF-EOS files should automatically read the latitude and longitude arrays associated with point and swath objects, or should use the HDF-EOS library routines that enable conversion of latitude and longitude coordinates to row and column indices for grid objects. In addition, several commercial packages can read the structural metadata to automatically geolocate the data arrays. Visit the NASA Goddard Earth Science, Data, and Information Services Center ( Data Tools Web page for more information about these tools.

To manually determine the geographic coverage of a data file, refer to the XML metadata (.xml) file delivered with the data. The HDF global text attribute StructMetadata.0 contains geolocation metadata for all data arrays. Level 2 swath data have latitude and longitude arrays called Geolocation Fields inside each swath VGroup. The structural metadata specifies the mapping of geolocation arrays to data arrays. For more information on Geolocation Fields, please consult Section 5.1.2 Geolocation Fields, page 27 of the HDF-EOS Library User's Guide, Volume 1. For Level 3 gridded data, the projection type and associated parameters are stored in the structural metadata according to GCTP conventions.

The free HDF-EOS to GeoTIFF Conversion Tool (HEG) allows you to gelocate, subset, stitch, and regrid certain HDF-EOS data sets. Please see the HEG Supported Products Web page for a list of all data sets supported by HEG.