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90 lines
4.2 KiB
HTML
90 lines
4.2 KiB
HTML
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<title>HFA -- Erdas Imagine .img</title>
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<body bgcolor="#ffffff">
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<h1>HFA -- Erdas Imagine .img</h1>
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GDAL supports Erdas Imagine .img format for read access and write. The
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driver supports reading overviews, palettes, and georeferencing. It
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supports the erdas band types
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u8, s8, u16, s16, u32, s32, f32, f64, c64 and c128.<p>
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Compressed and missing tiles in Erdas files should be handled properly on read.
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Files between 2GiB and 4GiB in size should work on Windows NT, and may work
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on some Unix platforms. Files with external spill files (needed for datasets
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larger than 2GiB) are also support for reading and writing.<p>
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Metadata reading and writing is supported at the dataset level, and for
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bands, but this is GDAL specific metadata - not metadata in an Imagine
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recognised form. The metadata is stored in a table called GDAL_MetaData with
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each column being a metadata item. The title is the key and the row 1 value
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is the value.<p>
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<h2>Creation Issues</h2>
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Erdas Imagine files can be created with any GDAL defined band type, including
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the complex types. Created files may have any number of bands. Pseudo-Color
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tables will be written if using the GDALDriver::CreateCopy() methodology.
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Most projections should be supported though translation of unusual datums
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(other than WGS84, WGS72, NAD83, and NAD27) may be problematic. <p>
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Creation Options:<p>
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<ul>
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<li> <b>BLOCKSIZE=blocksize</b>: Tile width/height (32-2048). Default=64<p>
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<li> <b>USE_SPILL=YES</b>: Force the generation of a spill file
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(by default spill file created for images larger 2GiB only). Default=NO<p>
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<li> <b>COMPRESSED=YES</b>: Create file as compressed. Use of spill file disables compression. Default=NO<p>
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<li> <b>NBITS=1/2/4</b>: Create file with special sub-byte data types.<p>
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<li> <b>PIXELTYPE=[DEFAULT/SIGNEDBYTE]</b>: By setting this to SIGNEDBYTE, a
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new Byte file can be forced to be written as signed byte.<p>
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<li> <b>AUX=YES</b>: To create a .aux file. Default=NO<p>
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<li> <b>IGNOREUTM=YES</b> : Ignore UTM when selecting coordinate system - will use Transverse Mercator. Only used for Create() method. Default=NO<p>
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<li> <b>STATISTICS=YES</b> : To generate statistics and a histogram. Default=NO<p>
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<li> <b>DEPENDENT_FILE=filename</b> : Name of dependent file (must not have absolute path). Optional<p>
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<li> <b>FORCETOPESTRING=YES</b>: Force use of ArcGIS PE String in file instead of Imagine coordinate system format. In some cases this improves ArcGIS coordinate system compatability.<p>
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</ul>
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Erdas Imagine supports external creation of overviews (with gdaladdo for
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instance). To force them to be created in an .rrd file (rather than inside
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the original .img) set the global config option HFA_USE_RRD=YES).<p>
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Layer names can be set and retrieved with the GDALSetDescription/GDALGetDescription calls on the Raster Band objects. <p>
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<h2>Configuration Options</h2>
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Currently two <a href="http://trac.osgeo.org/gdal/wiki/ConfigOptions">runtime configuration options</a> are supported by the HFA driver:
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<ul>
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<li> <b>HFA_USE_RRD=YES/NO</b> : Whether to force creation of external overviews in Erdas rrd format and with .rrd file name extension (gdaladdo with combination -ro --config USE_RRD YES creates overview file with .aux extension). <p>
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<li> <b>HFA_COMPRESS_OVR=YES/NO</b> : (GDAL >= 1.11) Whether to create compressed overviews.
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Default is to only create compressed overviews when the file is compressed. <p>
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This configuration option can be used when building external overviews for a base image that is not in Erdas Imagine format. Resulting overview file will use the rrd structure and have .aux extension.
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<pre>
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gdaladdo out.tif --config USE_RRD YES --config HFA_COMPRESS_OVR YES 2 4 8
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</pre>
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Erdas Imagine and older ArcGIS versions may recognize overviews for some image formats only if they have .rrd extension. In this case use:
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<pre>
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gdaladdo out.tif --config USE_RRD YES --config HFA_USE_RRD YES --config HFA_COMPRESS_OVR YES 2 4 8
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</pre>
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</li>
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</ul>
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See Also:<p>
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<ul>
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<li> Implemented as <tt>gdal/frmts/hfa/hfadataset.cpp</tt>.<p>
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<li> More information, and other tools are available on the
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<a href="http://home.gdal.org/projects/imagine/hfa_index.html">
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Imagine (.img) Reader</a> page.<p>
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<li> <a href="http://www.erdas.com/">Erdas.com</a><p>
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</ul>
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</body>
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</html>
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