HGT

File Format
Name	HGT
Ontology	Electronic File Formats Geospatial HGT
Extension(s)	.hgt

HGT (Height) files contain elevation data for regions of the Earth's surface, as acquired by the Shuttle Radar Topography Mission (STRM). The location of the region for data contained in a file is described by the name of the file itself. Each file describes a tile with a height of one degree of latitude and a width of one degree of longitude. The name of each file refers to the latitude and longitude at the lower left corner of the tile.

Format

Each file consists of a sequence of 16-bit signed values stored in big-endian byte order, arranged in row major order, meaning that the samples for each row are stored consecutively. The total number of values depends on the dimensions of the dataset held by each file. For 1 arc-second resolution data, each file will contain 3601 * 3601 values; for 3 arc-second resolution data, each file will contain 1201 * 1201 values.

Each value corresponds to the elevation measured in meters referenced to the WGS84 geoid.

The order of rows runs from north to south and the order of values in each row runs from west to east. This means that the first value in the last row in each file corresponds to the position specified by the name of the file. Each tile described by the data overlaps adjacent tiles to the north and south by a single row in each direction, and to the west and east by a single column in each direction. In other words, the first row of values in a file is the same as the last row of values in the file that describes the tile immediately to the north of it. Similarly, the last column of values will be the same as the first column of values in the file that describes the tile immediately to the east of it.

Identifiers

The filename extension .hgt is used.

Software

• python-hgt - Python module and tools for reading height (hgt) files.

Sample files

• SRTM Version 2.1 datasets
• Digital Elevation Data based on the SRTM data with fixes to areas with voids.

Links

• Shuttle Radar Topography Mission
• SRTM Topography
• Continent definitions showing the regions covered by the data.