|ER Mapper Raster
An ER Mapper Raster data set is made up of two files: a header file, with an .ERS extension and a data file of the same basename with no extension. The GDB library supports ER Mapper's Rasters for live linking, import and export.
The ER Mapper raster data file contains the data itself. The raster data is stored in a binary, Band-Interleaved-by-Line (BIL) format. The pixels' data type is defined in the accompanying header file. The data file name has no extension.
The ER Mapper data set header file is an ASCII file describing the raster data in the data file. The data set header file has the same base name as the data file it is describing, with the extension ".ers" added. For example, "Australia_DTM.ers" is a valid raster data set header file name for the raster data file "Australia_DTM."
The entire header file holds information about the data source and is contained in the DatasetHeader block. There are two compulsory sub-blocks, the CoordinateSpace block (to define the coordinate space and location) and the RasterInfo block (to define the characteristics of the data in the accompanying data file). The RasterInfo block my contain a number of optional sub-blocks.
The following section discusses some of the information found in the data set header file and what entries GDB uses/supports.
A DataType entry MUST exist and it MUST be "Raster". ByteOrder can be either "MSBFirst" (Most significant byte first) or "LSBFirst" (Least significant byte first). Datum can be "RAW" or one of the ER Mapper Supported Datums. If it is an unsupported datum, the Clarke 1866 datum is set by default. Projection can be "RAW" or one of the ER Mapper Supported Projections. If it is RAW or an unsupported projection, the projection defaults to METER by default. CoordinateType can be RAW, EN or LATLONG (notice there are no quotes for these entries). If it is RAW or EN (Easting/Northing), the coordinates in the header file will be interpreted as meters. If it is LATLONG, they will be interpreted as latitude and longitude expressed in degrees. Units can be expressed as "METERS" or an entry with "FOOT". All other entries are interpreted as meters, by default. CellType defines the data type of the pixels in the data file. Supported entries are: Unsigned8BitInteger Unsigned16BitInteger Signed16BitInteger IEEE4ByteReal Unsupported entries are: Signed8BitInteger Signed32BitInteger Unsigned32BitInteger IEEE8ByteReal NrOfLines, NrOfCellsPerLine and NrOfBands have integer values detailing number of lines, pixels and bands in the data set. RegistrationCellX and RegistrationCellY hold the data set X and Y (pixel/line) coordinates of the cell which corresponds to the RegistrationCoord block data. If they are not specified, the top left corner (0,0) is assumed to be the cell whose coordinates are provided as the Registration coordinates. The optional CellInfo block has two entries: the Xdimension and Ydimension. These identify the cell resolution. If they do not exist, the value 1 becomes the default. The optional RegistrationCoord block defines the location of the registration cell in the data set. This block is not optional, however, if the CoordinateType is EN or LATLONG. The entries in the RegistrationCoord block will be identified as Eastings/Northings, MetersX/MetersY or Latitude/Longitude (in decimal degrees). Channel descriptions for the bands contained in an ER Mapper raster are read from the Value entries in the BandId blocks. Otherwise they are listed as "Contents not specified." If a HeaderOffset entry appears, its value is interpreted as the length (in bytes) of any header data found in the data file. The CoordinateSpace's Rotation value is currently ignored by GDB. The RegionInfo, WarpControl and FFTInfo blocks are also ignored.
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