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What is BT?

BT is the file extension of the Binary Terrain file format. It was developed by Ben Discoe as part of the Virtual Terrain Product (VTP) with the aim to provide a simple way to store terrain information (elevation data) along with projection and position information in a single file. A BT file is easy to read and write, compact, and flexible in the sense that size and coordinate representation can be adjusted.

A BT file has a header of 256 bytes - 10 bytes indicating that it is a BT file; 4 bytes giving the width of the height grid; 4 bytes giving the height of the height grid; 2 bytes has the elevation grid point; 2 bytes of floating point values; 2 bytes has the horizontal units; 2 bytes indicates UTM zone; 2 bytes indicates the datum; 8 bytes specify the extents of the projection of the file; 8 bytes gives the right extent; 8 bytes gives the bottom extent; 8 bytes gives the top extent; 2 bytes gives the external projection; 4 bytes has the vertical units in meters; and 190 bytes are unused, serving as a pad to the rest of the header.

Following the header is an array of values containing the elevation values, the order being in increasing coordinates - from south to north. These elevation values are given in meters above sea level. All numeric values, both in the header and the data, use little endian encoding.

The Global Mapper v6.04 and higher can directly import and export the Binary Terrain file format. Alternatively, you can convert BT files to TIFF, PDF, JPEG, BMP with Total GIS Converter.

GIS converter
  • Convert GIS files in batch
  • Keep highest quality
gis converter
Total GIS Converter supports the following conversions with BT files:
  • BT to TIFF
  • BT to JPEG
  • BT to BMP
  • BT to PNG
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