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<html><head><title>OGDI -- OGDI Bridge</title></head><body bgcolor="#ffffff"><h1>OGDI -- OGDI Bridge</h1>OGDI raster data sources are supported by GDAL for reading. Both Matrixand Image families should be fully supported, as well as reading of colormapand projection metadata. The GDAL reader is intendedto be used with OGDI 3.1 drivers, but OGDI 3.0 drivers should also work.<p>OGDI datasets are opened within GDAL by selecting the GLTP url. Forinstance, gltp://gdal.velocet.ca/adrg/usr4/mpp1/adrg/TPSUS0101 would openthe ADRG dataset stored at /usr4/mpp1/adrg/TPSUS0101 on the machine gdal.velocet.ca (assuming it has an OGDI server running) using the 'adrg'driver. This default access to a whole datastore will attempt to representall layers (and all supported family types) as bands all at the resolutionand region reported by the datastore when initially accessed.<p>It is also possible to select a particular layer and access familyfrom an OGDI datastore by indicating the layer name family in the name.The GDAL dataset name gltp:/adrg/usr4/mpp1/adrg/TPUS0101:"TPUS0102.IMG":Matrix would selectthe layer named TPUS0102.IMG from the dataset /usr4/mpp1/adrg/TPUS0101 on the local system using the ADRG driver, and access the Matrix family.When a specific layer is accessed in this manner GDAL will attempt to determinethe region and resolution from the OGDI 3.1 capabilities document. Note thatOGDI 3.0 datastores must have the layer and family specified in the dataset name since they cannot be determined automatically.<p><pre>eg. gltp://gdal.velocet.ca/adrg/usr4/mpp1/adrg/TPUS0101 gltp:/adrg/usr4/mpp1/adrg/TPUS0101 gltp:/adrg/usr4/mpp1/adrg/TPUS0101:"TPUS0102.IMG":Matrix</pre>OGDI Matrix family layers (pseudocolored integer layers) are representedas a single band of raster data with a color table. Though the Matrix layerscontain 32bit integer values, they are represented through GDAL as eightlayers. All values over 255 are truncated to 255, and only 256 colormap entries are captured. While this works well for most Matrix layers, it isanticipated that at some point in the future Matrix layers with a largerdynamic range will be represented as other data types. <p>OGDI Image family layers may internally have a type of RGB (1) which isrepresented as three 8bit bands in GDAL, or Byte (2), UInt16 (3), Int16 (4) or Int32 (5). There is no support for floating points bands in OGDI 3.1.<p>The GDAL OGDI driver will represent OGDI datasources as having <i>arbitrary</i>overviews. Any GDAL raster read requests at a reduced resolution will bepassed on to the OGDI driver at that reduced resolution; potentially allowingefficient reading of overview information from OGDI datastores.<p>If an OGDI datastore is opened without selecting a layer name in the datasetname, and if the datastore has OGDI 3.1 style capabilities, the list of layerswill be made available as SUBDATASETS metadata. For instance, the <i>gdalinfo</i> command might report the following. This information can be used to establish available layers for direct access.<p><pre>Subdatasets: SUBDATASET_1_NAME=gltp:/adrg/usr4/mpp1/adrg/TPUS0101:"TPUS0101.IMG":Matrix SUBDATASET_1_DESC=TPUS0101.IMG as Matrix SUBDATASET_2_NAME=gltp:/adrg/usr4/mpp1/adrg/TPUS0101:"TPUS0102.IMG":Matrix SUBDATASET_2_DESC=TPUS0102.IMG as Matrix SUBDATASET_3_NAME=gltp:/adrg/usr4/mpp1/adrg/TPUS0101:"TPUS0101.IMG":Image SUBDATASET_3_DESC=TPUS0101.IMG as Image SUBDATASET_4_NAME=gltp:/adrg/usr4/mpp1/adrg/TPUS0101:"TPUS0102.IMG":Image SUBDATASET_4_DESC=TPUS0102.IMG as Image</pre>See Also:<p><ul><li> <a href="http://ogdi.sourceforge.net/">ogdi.sourceforge.net</a></ul></body></html>⌨️ 快捷键说明
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