File Format Guide
Files are available in a variety of formats. Some data collections are available in more than one format. The GLCF aims to provide spatial
data in standard formats, though legacy and special collections may retain others. This guide is provided to explain how users can identify
and utilize these formats. Anyone with questions may contact the GLCF directly. Translate the file nameFile names are standardized within collections whenever possible. Where imagery or products are generated externally, the GLCF has attempted to retain the naming standard of origin. Internally generated products are provided a standard name appropriate to the collection. Most file name reference the file's format. Please refer to the GLCF's Naming Conventions Format Guide to locate the file format reference contained within names.Identify the file format types used at GLCFPrimary file formats
Secondary files
Metadata files
Examples of how to load file formats in selected software
Details about the GeoTIFF formatGeoTIFF data is one of the most widely supported spatial data formats. GLCF uses this as a standard format, especially suited for imagery and other raster spatial files. GeoTIFF is a public domain format originated by Dr. Niles Ritter where basic TIFFs (Tag(ged) Image File Format) utilize geospatial tags imbedded within the TIFF file. Most remote sensing or GIS software will read these internal tags and automatically import a file's spatial coordinates, as well as any additional information (map projection, datum, byte order, etc.) which may be found in the tag. Software packages such as Photoshop or Microsoft Word which do not utilize spatial information will still be able to read in GeoTIFFs as normal TIFFs (in some cases support for TIFF 6.0 is required). In general the GeoTIFF format is also platform independent. Essentially, GeoTIFF is a TIFF file with location.Imagery in this format use the industry-wide TIFF image specification from Adobe and include a special header for storing georeferencing information. Scenes in GeoTIFF format can easily be read into any image software package that recognizes TIFFs and those that can understand the GeoTIFF-specific header can also automatically georeference the image. More information about GeoTIFF can be found at the GeoTIFF site at remotesensing.org. Details about the L1G/HDF/BSQ formatHDF is a format created by NASA for imagery and other raster spatial data. L1G is a level of processing for Landsat imagery that indicates the imagery is ready to use. L1G translates as "Level 1G", meaning the data has been processed to level 1 and is radiometrically and geometrically corrected. Since most Landsat 7 data files from the USGS include the "L1G" extension, the GLCF maintains this naming convention. Please note, however, that "L1G" indicates the processing level and not the actual file format.There are several versions of HDF. At the GLCF, L1G data is often in the "Unwrapped HDF" format. The GLCF provides each band of an image as a separate file, so the bands of each scene can be considered "Unwrapped" files, versus one file containing all bands. A special file, ending with "_HDF.L1G" accompanies each Landsat scene available in this format. Some spatial software will read the _HDF.L1G file accompanying a scene and use the information therein to handle the image as a single file, even though the reality is that the files are each distinct. Software reading HDF format will allow users to load the scene as a whole, or bands as separate entities. It is essential that the user copy both the band specific file plus the _HDF.L1G file. If spatial software will not read the _HDF.L1G file, the user may use the .L1G files as separate entities by treating them as BSQ files. This is the Band SeQuential binary format, which most spatial software can easily read. The requirement for this format, however, is that the user enter all the header information needed by the software to correctly display and locate the image. The software will prompt the user for details about the scene's corner coordinates, projection, datum, pixel size, number of rows and number of columns. To locate this information, open the metadata file appropriate to this scene (usually the "_MTL.L1G" for L1G files) in a text editor and copy the information. Details about the BSQ formatThis format stores imagery as a flat binary file with header information located in a separate metadata file. Although a wide variety of header files exist; software packages may or may not be able to read the header files to get the image dimensions or georeferencing information. If the software package cannot understand the header file, this information must be entered in manually.BSQ, or "Band Sequential" format, is a popular standard in image formats. Each image band is written as one independent file and, as such, BSQ can be a preferable format insofar as one does not have to read past ancillary data in an image stack. As opposed to formats such as a multi-band GeoTIFF (where all the bands are in one file), BSQ data sets give the user the option of only downloading the relevant bands. Details about the Fast formatThe Fast Format is an example of the BSQ format with a header file, independent bands followed by "End of File" markers, followed, in turn, by an "End of Volume" marker.Details about the Mr.Sid formatThis format is proprietary to LizardTech, where imagery is compressed but easily displayed. Some spatial software does not support this image format, though a free viewer can be downloaded from LizardTech.
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The Global Land Cover Facility University of Maryland, Copyright 2006 |
