BIL (Band Interleaved by Line)

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Introduction

BIL (Band Interleaved by Line) is a geospatial data format commonly used to store remote sensing images and geographic information system (GIS) data. BIL is a multi-band image storage method with interleaved lines. Its core feature is to store multi-band image data alternately in the file in line order. That is, each line of data contains the pixel values of all bands, and the storage order is: the first line of band 1, the first line of band 2, …, the first line of band n, and then the second line of all bands, and so on.

File Structure

The BIL file itself only contains the raw image data (i.e. pixel values) and does not provide metadata about the image attributes. Therefore, BIL files are usually used with the following supporting files:

HDR file (header file): stores image metadata, such as the number of bands, number of rows and columns, data type, geographic reference information, etc.
AUX file (auxiliary file): used to store geospatial attribute information, usually automatically generated by GIS software.

Key features of BIL files

Storage method: arranged in the order of “row-band-pixel”.
Data type: supports multiple data formats, including integer type (int), floating point type (float), etc., to meet different accuracy requirements.
Extensibility: metadata information can be flexibly expanded through HDR files to facilitate compatibility with other GIS tools.

Pros

1. Efficient row data access: Since data is stored in rows, BIL format has faster access speed for operations within the row range (such as row cutting and local data extraction).

2. Strong compatibility: BIL is a standardized format that can be directly read and processed by many remote sensing and GIS tools (such as ENVI, ArcGIS, etc.).

3. Multi-band support: Supports multiple band storage, suitable for the management and analysis of multispectral or hyperspectral data such as remote sensing images.

4. Flexible metadata storage: The supporting HDR file can provide detailed geographic information and image attribute information, which is convenient for subsequent processing and analysis.

Cons

1. Large storage space: Compared with compressed formats (such as GeoTIFF, JPEG2000), BIL files are uncompressed formats with large file sizes, which are not suitable for storing and transmitting large-scale data.

2. Line-by-line storage limitations: For global data scenarios that require frequent access to a single band, the access efficiency may not be as efficient as the band interleaved (BIP) or pixel interleaved (BSQ) storage methods.

3. Dependence on supporting files: The loss of HDR files will make the image data difficult to parse, increasing the complexity of file management.

Application Scenario

In remote sensing image processing, the BIL format is suitable for the storage and analysis of multispectral and hyperspectral data. For example, land classification, vegetation index calculation, geological exploration, etc. of satellite images can all use the BIL format to efficiently store and process multi-band data. In the field of hydrology and meteorology, the BIL format is often used to store and analyze spatial data such as surface temperature and rainfall distribution. In conjunction with HDR files, it can achieve rapid positioning and calculation of geographic spatial information. In addition, BIL files are also widely used in urban planning and resource management. With its high-precision image data support, planners can more clearly analyze urban changes and resource distribution.