# Terragen -- Terragen™ Terrain File

Driver short name

Terragen

Driver built-in by default

This driver is built-in by default

Terragen terrain files store 16-bit elevation values with optional gridspacing (but not positioning). The file extension for Terragen heightfields is "TER" or "TERRAIN" (which in the former case is the same as Leveller, but the driver only recognizes Terragen files). The driver ID is "Terragen". The dataset is file-based and has only one elevation band. Void elevations are not supported. Pixels are considered points.

## Driver capabilities

Supports CreateCopy()

This driver supports the `GDALDriver::CreateCopy()` operation

Supports Create()

This driver supports the `GDALDriver::Create()` operation

Supports Georeferencing

This driver supports georeferencing

Supports VirtualIO

This driver supports virtual I/O operations (/vsimem/, etc.)

## Reading

> `dataset::GetProjectionRef()` returns a local coordinate system using meters.

> `band::GetUnitType()` returns meters.

> Elevations are `Int16`. You must use the `band::GetScale()` and `band::GetOffset()` to convert them to meters.

## Writing

> Use the `Create` call. Set the `MINUSERPIXELVALUE` option (a float) to the lowest elevation of your elevation data, and `MAXUSERPIXELVALUE` to the highest. The units must match the elevation units you will give to `band::SetUnitType()`.

> Call `dataset::SetProjection()` and `dataset::SetGeoTransform()` with your coordinate system details. Otherwise, the driver will not encode physical elevations properly. Geographic (degree-based) coordinate systems will be converted to a local meter-based system.

> To maintain precision, a best-fit baseheight and scaling will be used to use as much of the 16-bit range as possible.

> Elevations are `Float32`.

## Roundtripping

> Errors per trip tend to be a few centimeters for elevations and up to one or two meters for ground extents if degree-based coordinate systems are written. Large degree-based DEMs incur unavoidable distortions since the driver currently only uses meters.

## See Also

- Implemented as terragendataset.cpp.

- See readme.txt for installation and support information.

- Terragen Terrain File Specification.