Long name | PCI DEM Index file |
Short name | index.txt |
File extension(s) | .txt |
The DEM Index file is a text-format file that lists all DEM files or tiles in a source directory to be used for DEM processing. The DEM Index file is treated as a single virtual DEM, eliminating the need to merge the DEM tiles into a single file.
The GDB library supports the DEM Index file in text format for input only; GDB does not write to this format.
The following text shows an example of a DEM index file.
MAPUNITS LONG/LAT D000 DATATYPE 16S DBEC 1 BACKELEV -32768.000 ELEVREF MSL ELEVUNIT METER ELFACTOR 0.000 1.000000000000 RES_XY 0.0008333333333333 0.0008333333333333 #Filename ULX ULY LRX LRY srtm_01_02.tif -180.000416666676760 55.000416618227803 -174.999583333343420 49.999583284894470 srtm_01_07.tif -180.000416690891140 30.000417247801863 -174.999583357557810 24.999583914468531 srtm_01_12.tif -180.000416690891140 5.000416642442191 -174.999583357557810 -0.000416690891143 srtm_01_15.tif -180.000416666676760 -9.999582994342006 -174.999583333343420 -15.000416327675339 srtm_01_16.tif -180.000416666676760 -14.999583115413941 -174.999583333343420 -20.000416448747274 srtm_01_17.tif -180.000416666676760 -19.999583236485876 -174.999583333343420 -25.000416569819208 srtm_01_18.tif -180.000416666676760 -24.999583357557810 -174.999583333343420 -30.000416690891143
The first eight lines of the file describe common values that apply to all images; they must be in the order shown in the example with no comments or blank lines between them. The remaining lines describe the image boundary records for all the images in the DEM tile data set. Comments (lines beginning with a #) are allowed in the DEM tile file list.
DATATYPE: Specifies the data type of the files.
DBEC: Specifies the channel number for the input digital elevation model (DEM) elevation channel to be processed.
BACKELEV: Specifies the background elevation (NoData) value in the input DEM elevation layer.
ELEVREF: Specifies the vertical reference for the elevation values contained in the source DEM, or for the constant ELFACTOR value, if it is used.
ELEVUNIT: Specifies the units of the elevation values that are stored as pixel values in the input DEM, as specified either by FILEDEM or by the first entry in ELFACTOR.
ELFACTOR: If an input digital elevation model (FILEDEM) is specified, the value of this parameter is used to shift and scale the DEM pixel values to values in the units indicated by the value of the ELEVUNIT parameter.
RES_XY: Specifies the X and Y image resolution values.
As individual raster tiles are accessed, their properties are compared with the values listed in the DEM index file. If they do not conform to the indicated values, an error message appears in the log.
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