# USGSDEM -- USGS ASCII DEM (and CDED)

Driver short name

USGSDEM

Driver built-in by default

This driver is built-in by default

GDAL includes support for reading USGS ASCII DEM files. This is the traditional format used by USGS before being replaced by SDTS, and is the format used for CDED DEM data products from Canada. Most popular variations on USGS DEM files should be supported, including correct recognition of coordinate system, and georeferenced positioning.

The 7.5 minute (UTM grid) USGS DEM files will generally have regions of missing data around the edges, and these are properly marked with a nodata value. Elevation values in USGS DEM files may be in meters or feet, and this will be indicated by the return value of GDALRasterBand::GetUnitType() (either "m" or "ft").

Note that USGS DEM files are represented as one big tile. This may cause cache thrashing problems if the GDAL tile cache size is small. It will also result in a substantial delay when the first pixel is read as the whole file will be ingested.

Some of the code for implementing usgsdemdataset.cpp was derived from VTP code by Ben Discoe. See the Virtual Terrain project for more information on VTP.

## Driver capabilities

Supports Georeferencing

This driver supports georeferencing

Supports VirtualIO

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

NOTE: Implemented as usgsdemdataset.cpp.

The USGS DEM reading code in GDAL was derived from the importer in the VTP software. The export capability was developed with the financial support of the Yukon Department of Environment.