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.