What is a HDR file?
An HDR file is a GIS header file that contains header information for a Band interleaved by line (.BIL) file. It describes the image data and has the same name as that of the image file. An HDR file comprises of a set of entries, each of which describes a particular attribute of the image. The HDR file describes the layout and formatting of the BIL file for translation to real world coordinates in combination with a separate georeferencing file.
HDR File Format
HDR files are saved in ASCII text file format. It contains a set of entries where each entry describes a particular attribute of the image. Each HDR file has the following format:
<keyword> <value>
<keyword> - It indicates the particular attribute that is being set
<value> - It is the value to which the attribute is being set
There is no limitation on the order of the entries in the header. However, each entry must be on a separate line of the line to comply with the parsing method used by HDR readers.
Summary of Keywords used in HDR File
| Keyword | Acceptable Value | Default |
|---|---|---|
| nrows | any integer > 0 | none |
| ncols | any integer > 0 | none |
| nbands | any integer > 0 | 1 |
| nbits | 1, 4, 8, 16, 32 | 8 |
| byteorder | I = Intel;M = Motorola | same as host machine |
| layout | bil, bip, bsq | bil |
| skipbytes | any integer ≥ 0 | 0 |
| ulxmap | any real number | 0 |
| ulymap | any real number | nrows - 1 |
| xdim | any real number | 1 |
| ydim | any real number | 1 |
| bandrowbytes | any integer > 0 | smallest integer ≥ (ncols x nbits) / 8 |
| totalrowbytes | any integer > 0 | for bil: nbands x bandrowbytes;for bip: smallest integer ≥ (ncols x nbands x nbits) / 8 |
| bandgapbytes | any integer ≥ 0 | 0 |
