Wade,
BIL files are the simplest form of representing gridded data (such as DEMs,
satellite images etc). BIL files can be multi-band, commonly 3-band files
are used for imagery where band 1 represents red (usually in the range
0-255), band 2 represents green and band 3 represents blue.
Multi-band BIL files are structured (as their name implies) with the bands
interleaved for each line. For a 3 band BIL, the structure is thus (with
line 1, column 1 at the top left corner):
Line 1 Band 1
Line 1 Band 2
Line 1 Band 3
Line 2 Band 1
Line 2 Band 2
Line 3 Band 3
etc.
BIL files are usually binary with each element stored as either an 8 bit, 16
bit, 32 bit signed/unsigned integer, 4 or 8 byte real value. BIL files can
also be in ASCII format (though they need converting to binary before being
displayed in most software).
In order to navigate through a BIL file, a reading program therefore just
needs to know the number of rows, columns, bands and the size of each
element in order to compute the offset and retrieve the required values.
The grid geometry (rows, cols, bands, element size) is stored in an external
header file (.ers for ER Mapper, .hdr for MapInfo, ArcView etc).
MapInfo will display single band 8-bit BIL files, and 3 band 8-bit per band
(also referred to as 24-bit) BIL files, but only if the supporting .hdr file
is present and correct. MapInfo will not display other types of BIL files.
Other software, such as Discover (see www.encom.com.au) or ER Mapper can
also be used to display BIL files in MapInfo and these provide a greater
range of functionality.
Martin Higham
Manager - GIS Services
Encom Technology ph (61 3) 9428 4088
PO Box 727, Richmond fx (61 3) 9428 0470
VIC, 3121, Australia mobile 0414 624117
www.encom.com.au
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of
> [EMAIL PROTECTED]
> Sent: Thursday, 9 September 1999 4:43
> To: [EMAIL PROTECTED]
> Subject: MI band interleave files (.BIL)
>
>
> All,
> Does anyone know of *good* reference documentation that describes file
> format and structure
> for single and triple band, band interleave files?
>
> AdvTHANKSance,
> Wade
>
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